kernel/
dma.rs

1// SPDX-License-Identifier: GPL-2.0
2
3//! Direct memory access (DMA).
4//!
5//! C header: [`include/linux/dma-mapping.h`](srctree/include/linux/dma-mapping.h)
6
7use crate::{
8    bindings, build_assert, device,
9    device::{Bound, Core},
10    error::{to_result, Result},
11    prelude::*,
12    sync::aref::ARef,
13    transmute::{AsBytes, FromBytes},
14};
15
16/// DMA address type.
17///
18/// Represents a bus address used for Direct Memory Access (DMA) operations.
19///
20/// This is an alias of the kernel's `dma_addr_t`, which may be `u32` or `u64` depending on
21/// `CONFIG_ARCH_DMA_ADDR_T_64BIT`.
22///
23/// Note that this may be `u64` even on 32-bit architectures.
24pub type DmaAddress = bindings::dma_addr_t;
25
26/// Trait to be implemented by DMA capable bus devices.
27///
28/// The [`dma::Device`](Device) trait should be implemented by bus specific device representations,
29/// where the underlying bus is DMA capable, such as [`pci::Device`](::kernel::pci::Device) or
30/// [`platform::Device`](::kernel::platform::Device).
31pub trait Device: AsRef<device::Device<Core>> {
32    /// Set up the device's DMA streaming addressing capabilities.
33    ///
34    /// This method is usually called once from `probe()` as soon as the device capabilities are
35    /// known.
36    ///
37    /// # Safety
38    ///
39    /// This method must not be called concurrently with any DMA allocation or mapping primitives,
40    /// such as [`CoherentAllocation::alloc_attrs`].
41    unsafe fn dma_set_mask(&self, mask: DmaMask) -> Result {
42        // SAFETY:
43        // - By the type invariant of `device::Device`, `self.as_ref().as_raw()` is valid.
44        // - The safety requirement of this function guarantees that there are no concurrent calls
45        //   to DMA allocation and mapping primitives using this mask.
46        to_result(unsafe { bindings::dma_set_mask(self.as_ref().as_raw(), mask.value()) })
47    }
48
49    /// Set up the device's DMA coherent addressing capabilities.
50    ///
51    /// This method is usually called once from `probe()` as soon as the device capabilities are
52    /// known.
53    ///
54    /// # Safety
55    ///
56    /// This method must not be called concurrently with any DMA allocation or mapping primitives,
57    /// such as [`CoherentAllocation::alloc_attrs`].
58    unsafe fn dma_set_coherent_mask(&self, mask: DmaMask) -> Result {
59        // SAFETY:
60        // - By the type invariant of `device::Device`, `self.as_ref().as_raw()` is valid.
61        // - The safety requirement of this function guarantees that there are no concurrent calls
62        //   to DMA allocation and mapping primitives using this mask.
63        to_result(unsafe { bindings::dma_set_coherent_mask(self.as_ref().as_raw(), mask.value()) })
64    }
65
66    /// Set up the device's DMA addressing capabilities.
67    ///
68    /// This is a combination of [`Device::dma_set_mask`] and [`Device::dma_set_coherent_mask`].
69    ///
70    /// This method is usually called once from `probe()` as soon as the device capabilities are
71    /// known.
72    ///
73    /// # Safety
74    ///
75    /// This method must not be called concurrently with any DMA allocation or mapping primitives,
76    /// such as [`CoherentAllocation::alloc_attrs`].
77    unsafe fn dma_set_mask_and_coherent(&self, mask: DmaMask) -> Result {
78        // SAFETY:
79        // - By the type invariant of `device::Device`, `self.as_ref().as_raw()` is valid.
80        // - The safety requirement of this function guarantees that there are no concurrent calls
81        //   to DMA allocation and mapping primitives using this mask.
82        to_result(unsafe {
83            bindings::dma_set_mask_and_coherent(self.as_ref().as_raw(), mask.value())
84        })
85    }
86}
87
88/// A DMA mask that holds a bitmask with the lowest `n` bits set.
89///
90/// Use [`DmaMask::new`] or [`DmaMask::try_new`] to construct a value. Values
91/// are guaranteed to never exceed the bit width of `u64`.
92///
93/// This is the Rust equivalent of the C macro `DMA_BIT_MASK()`.
94#[derive(Debug, Clone, Copy, PartialEq, Eq)]
95pub struct DmaMask(u64);
96
97impl DmaMask {
98    /// Constructs a `DmaMask` with the lowest `n` bits set to `1`.
99    ///
100    /// For `n <= 64`, sets exactly the lowest `n` bits.
101    /// For `n > 64`, results in a build error.
102    ///
103    /// # Examples
104    ///
105    /// ```
106    /// use kernel::dma::DmaMask;
107    ///
108    /// let mask0 = DmaMask::new::<0>();
109    /// assert_eq!(mask0.value(), 0);
110    ///
111    /// let mask1 = DmaMask::new::<1>();
112    /// assert_eq!(mask1.value(), 0b1);
113    ///
114    /// let mask64 = DmaMask::new::<64>();
115    /// assert_eq!(mask64.value(), u64::MAX);
116    ///
117    /// // Build failure.
118    /// // let mask_overflow = DmaMask::new::<100>();
119    /// ```
120    #[inline]
121    pub const fn new<const N: u32>() -> Self {
122        let Ok(mask) = Self::try_new(N) else {
123            build_error!("Invalid DMA Mask.");
124        };
125
126        mask
127    }
128
129    /// Constructs a `DmaMask` with the lowest `n` bits set to `1`.
130    ///
131    /// For `n <= 64`, sets exactly the lowest `n` bits.
132    /// For `n > 64`, returns [`EINVAL`].
133    ///
134    /// # Examples
135    ///
136    /// ```
137    /// use kernel::dma::DmaMask;
138    ///
139    /// let mask0 = DmaMask::try_new(0)?;
140    /// assert_eq!(mask0.value(), 0);
141    ///
142    /// let mask1 = DmaMask::try_new(1)?;
143    /// assert_eq!(mask1.value(), 0b1);
144    ///
145    /// let mask64 = DmaMask::try_new(64)?;
146    /// assert_eq!(mask64.value(), u64::MAX);
147    ///
148    /// let mask_overflow = DmaMask::try_new(100);
149    /// assert!(mask_overflow.is_err());
150    /// # Ok::<(), Error>(())
151    /// ```
152    #[inline]
153    pub const fn try_new(n: u32) -> Result<Self> {
154        Ok(Self(match n {
155            0 => 0,
156            1..=64 => u64::MAX >> (64 - n),
157            _ => return Err(EINVAL),
158        }))
159    }
160
161    /// Returns the underlying `u64` bitmask value.
162    #[inline]
163    pub const fn value(&self) -> u64 {
164        self.0
165    }
166}
167
168/// Possible attributes associated with a DMA mapping.
169///
170/// They can be combined with the operators `|`, `&`, and `!`.
171///
172/// Values can be used from the [`attrs`] module.
173///
174/// # Examples
175///
176/// ```
177/// # use kernel::device::{Bound, Device};
178/// use kernel::dma::{attrs::*, CoherentAllocation};
179///
180/// # fn test(dev: &Device<Bound>) -> Result {
181/// let attribs = DMA_ATTR_FORCE_CONTIGUOUS | DMA_ATTR_NO_WARN;
182/// let c: CoherentAllocation<u64> =
183///     CoherentAllocation::alloc_attrs(dev, 4, GFP_KERNEL, attribs)?;
184/// # Ok::<(), Error>(()) }
185/// ```
186#[derive(Clone, Copy, PartialEq)]
187#[repr(transparent)]
188pub struct Attrs(u32);
189
190impl Attrs {
191    /// Get the raw representation of this attribute.
192    pub(crate) fn as_raw(self) -> crate::ffi::c_ulong {
193        self.0 as crate::ffi::c_ulong
194    }
195
196    /// Check whether `flags` is contained in `self`.
197    pub fn contains(self, flags: Attrs) -> bool {
198        (self & flags) == flags
199    }
200}
201
202impl core::ops::BitOr for Attrs {
203    type Output = Self;
204    fn bitor(self, rhs: Self) -> Self::Output {
205        Self(self.0 | rhs.0)
206    }
207}
208
209impl core::ops::BitAnd for Attrs {
210    type Output = Self;
211    fn bitand(self, rhs: Self) -> Self::Output {
212        Self(self.0 & rhs.0)
213    }
214}
215
216impl core::ops::Not for Attrs {
217    type Output = Self;
218    fn not(self) -> Self::Output {
219        Self(!self.0)
220    }
221}
222
223/// DMA mapping attributes.
224pub mod attrs {
225    use super::Attrs;
226
227    /// Specifies that reads and writes to the mapping may be weakly ordered, that is that reads
228    /// and writes may pass each other.
229    pub const DMA_ATTR_WEAK_ORDERING: Attrs = Attrs(bindings::DMA_ATTR_WEAK_ORDERING);
230
231    /// Specifies that writes to the mapping may be buffered to improve performance.
232    pub const DMA_ATTR_WRITE_COMBINE: Attrs = Attrs(bindings::DMA_ATTR_WRITE_COMBINE);
233
234    /// Lets the platform to avoid creating a kernel virtual mapping for the allocated buffer.
235    pub const DMA_ATTR_NO_KERNEL_MAPPING: Attrs = Attrs(bindings::DMA_ATTR_NO_KERNEL_MAPPING);
236
237    /// Allows platform code to skip synchronization of the CPU cache for the given buffer assuming
238    /// that it has been already transferred to 'device' domain.
239    pub const DMA_ATTR_SKIP_CPU_SYNC: Attrs = Attrs(bindings::DMA_ATTR_SKIP_CPU_SYNC);
240
241    /// Forces contiguous allocation of the buffer in physical memory.
242    pub const DMA_ATTR_FORCE_CONTIGUOUS: Attrs = Attrs(bindings::DMA_ATTR_FORCE_CONTIGUOUS);
243
244    /// Hints DMA-mapping subsystem that it's probably not worth the time to try
245    /// to allocate memory to in a way that gives better TLB efficiency.
246    pub const DMA_ATTR_ALLOC_SINGLE_PAGES: Attrs = Attrs(bindings::DMA_ATTR_ALLOC_SINGLE_PAGES);
247
248    /// This tells the DMA-mapping subsystem to suppress allocation failure reports (similarly to
249    /// `__GFP_NOWARN`).
250    pub const DMA_ATTR_NO_WARN: Attrs = Attrs(bindings::DMA_ATTR_NO_WARN);
251
252    /// Indicates that the buffer is fully accessible at an elevated privilege level (and
253    /// ideally inaccessible or at least read-only at lesser-privileged levels).
254    pub const DMA_ATTR_PRIVILEGED: Attrs = Attrs(bindings::DMA_ATTR_PRIVILEGED);
255
256    /// Indicates that the buffer is MMIO memory.
257    pub const DMA_ATTR_MMIO: Attrs = Attrs(bindings::DMA_ATTR_MMIO);
258}
259
260/// DMA data direction.
261///
262/// Corresponds to the C [`enum dma_data_direction`].
263///
264/// [`enum dma_data_direction`]: srctree/include/linux/dma-direction.h
265#[derive(Copy, Clone, PartialEq, Eq, Debug)]
266#[repr(u32)]
267pub enum DataDirection {
268    /// The DMA mapping is for bidirectional data transfer.
269    ///
270    /// This is used when the buffer can be both read from and written to by the device.
271    /// The cache for the corresponding memory region is both flushed and invalidated.
272    Bidirectional = Self::const_cast(bindings::dma_data_direction_DMA_BIDIRECTIONAL),
273
274    /// The DMA mapping is for data transfer from memory to the device (write).
275    ///
276    /// The CPU has prepared data in the buffer, and the device will read it.
277    /// The cache for the corresponding memory region is flushed before device access.
278    ToDevice = Self::const_cast(bindings::dma_data_direction_DMA_TO_DEVICE),
279
280    /// The DMA mapping is for data transfer from the device to memory (read).
281    ///
282    /// The device will write data into the buffer for the CPU to read.
283    /// The cache for the corresponding memory region is invalidated before CPU access.
284    FromDevice = Self::const_cast(bindings::dma_data_direction_DMA_FROM_DEVICE),
285
286    /// The DMA mapping is not for data transfer.
287    ///
288    /// This is primarily for debugging purposes. With this direction, the DMA mapping API
289    /// will not perform any cache coherency operations.
290    None = Self::const_cast(bindings::dma_data_direction_DMA_NONE),
291}
292
293impl DataDirection {
294    /// Casts the bindgen-generated enum type to a `u32` at compile time.
295    ///
296    /// This function will cause a compile-time error if the underlying value of the
297    /// C enum is out of bounds for `u32`.
298    const fn const_cast(val: bindings::dma_data_direction) -> u32 {
299        // CAST: The C standard allows compilers to choose different integer types for enums.
300        // To safely check the value, we cast it to a wide signed integer type (`i128`)
301        // which can hold any standard C integer enum type without truncation.
302        let wide_val = val as i128;
303
304        // Check if the value is outside the valid range for the target type `u32`.
305        // CAST: `u32::MAX` is cast to `i128` to match the type of `wide_val` for the comparison.
306        if wide_val < 0 || wide_val > u32::MAX as i128 {
307            // Trigger a compile-time error in a const context.
308            build_error!("C enum value is out of bounds for the target type `u32`.");
309        }
310
311        // CAST: This cast is valid because the check above guarantees that `wide_val`
312        // is within the representable range of `u32`.
313        wide_val as u32
314    }
315}
316
317impl From<DataDirection> for bindings::dma_data_direction {
318    /// Returns the raw representation of [`enum dma_data_direction`].
319    fn from(direction: DataDirection) -> Self {
320        // CAST: `direction as u32` gets the underlying representation of our `#[repr(u32)]` enum.
321        // The subsequent cast to `Self` (the bindgen type) assumes the C enum is compatible
322        // with the enum variants of `DataDirection`, which is a valid assumption given our
323        // compile-time checks.
324        direction as u32 as Self
325    }
326}
327
328/// An abstraction of the `dma_alloc_coherent` API.
329///
330/// This is an abstraction around the `dma_alloc_coherent` API which is used to allocate and map
331/// large coherent DMA regions.
332///
333/// A [`CoherentAllocation`] instance contains a pointer to the allocated region (in the
334/// processor's virtual address space) and the device address which can be given to the device
335/// as the DMA address base of the region. The region is released once [`CoherentAllocation`]
336/// is dropped.
337///
338/// # Invariants
339///
340/// - For the lifetime of an instance of [`CoherentAllocation`], the `cpu_addr` is a valid pointer
341///   to an allocated region of coherent memory and `dma_handle` is the DMA address base of the
342///   region.
343/// - The size in bytes of the allocation is equal to `size_of::<T> * count`.
344/// - `size_of::<T> * count` fits into a `usize`.
345// TODO
346//
347// DMA allocations potentially carry device resources (e.g.IOMMU mappings), hence for soundness
348// reasons DMA allocation would need to be embedded in a `Devres` container, in order to ensure
349// that device resources can never survive device unbind.
350//
351// However, it is neither desirable nor necessary to protect the allocated memory of the DMA
352// allocation from surviving device unbind; it would require RCU read side critical sections to
353// access the memory, which may require subsequent unnecessary copies.
354//
355// Hence, find a way to revoke the device resources of a `CoherentAllocation`, but not the
356// entire `CoherentAllocation` including the allocated memory itself.
357pub struct CoherentAllocation<T: AsBytes + FromBytes> {
358    dev: ARef<device::Device>,
359    dma_handle: DmaAddress,
360    count: usize,
361    cpu_addr: *mut T,
362    dma_attrs: Attrs,
363}
364
365impl<T: AsBytes + FromBytes> CoherentAllocation<T> {
366    /// Allocates a region of `size_of::<T> * count` of coherent memory.
367    ///
368    /// # Examples
369    ///
370    /// ```
371    /// # use kernel::device::{Bound, Device};
372    /// use kernel::dma::{attrs::*, CoherentAllocation};
373    ///
374    /// # fn test(dev: &Device<Bound>) -> Result {
375    /// let c: CoherentAllocation<u64> =
376    ///     CoherentAllocation::alloc_attrs(dev, 4, GFP_KERNEL, DMA_ATTR_NO_WARN)?;
377    /// # Ok::<(), Error>(()) }
378    /// ```
379    pub fn alloc_attrs(
380        dev: &device::Device<Bound>,
381        count: usize,
382        gfp_flags: kernel::alloc::Flags,
383        dma_attrs: Attrs,
384    ) -> Result<CoherentAllocation<T>> {
385        build_assert!(
386            core::mem::size_of::<T>() > 0,
387            "It doesn't make sense for the allocated type to be a ZST"
388        );
389
390        let size = count
391            .checked_mul(core::mem::size_of::<T>())
392            .ok_or(EOVERFLOW)?;
393        let mut dma_handle = 0;
394        // SAFETY: Device pointer is guaranteed as valid by the type invariant on `Device`.
395        let ret = unsafe {
396            bindings::dma_alloc_attrs(
397                dev.as_raw(),
398                size,
399                &mut dma_handle,
400                gfp_flags.as_raw(),
401                dma_attrs.as_raw(),
402            )
403        };
404        if ret.is_null() {
405            return Err(ENOMEM);
406        }
407        // INVARIANT:
408        // - We just successfully allocated a coherent region which is accessible for
409        //   `count` elements, hence the cpu address is valid. We also hold a refcounted reference
410        //   to the device.
411        // - The allocated `size` is equal to `size_of::<T> * count`.
412        // - The allocated `size` fits into a `usize`.
413        Ok(Self {
414            dev: dev.into(),
415            dma_handle,
416            count,
417            cpu_addr: ret.cast::<T>(),
418            dma_attrs,
419        })
420    }
421
422    /// Performs the same functionality as [`CoherentAllocation::alloc_attrs`], except the
423    /// `dma_attrs` is 0 by default.
424    pub fn alloc_coherent(
425        dev: &device::Device<Bound>,
426        count: usize,
427        gfp_flags: kernel::alloc::Flags,
428    ) -> Result<CoherentAllocation<T>> {
429        CoherentAllocation::alloc_attrs(dev, count, gfp_flags, Attrs(0))
430    }
431
432    /// Returns the number of elements `T` in this allocation.
433    ///
434    /// Note that this is not the size of the allocation in bytes, which is provided by
435    /// [`Self::size`].
436    pub fn count(&self) -> usize {
437        self.count
438    }
439
440    /// Returns the size in bytes of this allocation.
441    pub fn size(&self) -> usize {
442        // INVARIANT: The type invariant of `Self` guarantees that `size_of::<T> * count` fits into
443        // a `usize`.
444        self.count * core::mem::size_of::<T>()
445    }
446
447    /// Returns the base address to the allocated region in the CPU's virtual address space.
448    pub fn start_ptr(&self) -> *const T {
449        self.cpu_addr
450    }
451
452    /// Returns the base address to the allocated region in the CPU's virtual address space as
453    /// a mutable pointer.
454    pub fn start_ptr_mut(&mut self) -> *mut T {
455        self.cpu_addr
456    }
457
458    /// Returns a DMA handle which may be given to the device as the DMA address base of
459    /// the region.
460    pub fn dma_handle(&self) -> DmaAddress {
461        self.dma_handle
462    }
463
464    /// Returns a DMA handle starting at `offset` (in units of `T`) which may be given to the
465    /// device as the DMA address base of the region.
466    ///
467    /// Returns `EINVAL` if `offset` is not within the bounds of the allocation.
468    pub fn dma_handle_with_offset(&self, offset: usize) -> Result<DmaAddress> {
469        if offset >= self.count {
470            Err(EINVAL)
471        } else {
472            // INVARIANT: The type invariant of `Self` guarantees that `size_of::<T> * count` fits
473            // into a `usize`, and `offset` is inferior to `count`.
474            Ok(self.dma_handle + (offset * core::mem::size_of::<T>()) as DmaAddress)
475        }
476    }
477
478    /// Common helper to validate a range applied from the allocated region in the CPU's virtual
479    /// address space.
480    fn validate_range(&self, offset: usize, count: usize) -> Result {
481        if offset.checked_add(count).ok_or(EOVERFLOW)? > self.count {
482            return Err(EINVAL);
483        }
484        Ok(())
485    }
486
487    /// Returns the data from the region starting from `offset` as a slice.
488    /// `offset` and `count` are in units of `T`, not the number of bytes.
489    ///
490    /// For ringbuffer type of r/w access or use-cases where the pointer to the live data is needed,
491    /// [`CoherentAllocation::start_ptr`] or [`CoherentAllocation::start_ptr_mut`] could be used
492    /// instead.
493    ///
494    /// # Safety
495    ///
496    /// * Callers must ensure that the device does not read/write to/from memory while the returned
497    ///   slice is live.
498    /// * Callers must ensure that this call does not race with a write to the same region while
499    ///   the returned slice is live.
500    pub unsafe fn as_slice(&self, offset: usize, count: usize) -> Result<&[T]> {
501        self.validate_range(offset, count)?;
502        // SAFETY:
503        // - The pointer is valid due to type invariant on `CoherentAllocation`,
504        //   we've just checked that the range and index is within bounds. The immutability of the
505        //   data is also guaranteed by the safety requirements of the function.
506        // - `offset + count` can't overflow since it is smaller than `self.count` and we've checked
507        //   that `self.count` won't overflow early in the constructor.
508        Ok(unsafe { core::slice::from_raw_parts(self.cpu_addr.add(offset), count) })
509    }
510
511    /// Performs the same functionality as [`CoherentAllocation::as_slice`], except that a mutable
512    /// slice is returned.
513    ///
514    /// # Safety
515    ///
516    /// * Callers must ensure that the device does not read/write to/from memory while the returned
517    ///   slice is live.
518    /// * Callers must ensure that this call does not race with a read or write to the same region
519    ///   while the returned slice is live.
520    pub unsafe fn as_slice_mut(&mut self, offset: usize, count: usize) -> Result<&mut [T]> {
521        self.validate_range(offset, count)?;
522        // SAFETY:
523        // - The pointer is valid due to type invariant on `CoherentAllocation`,
524        //   we've just checked that the range and index is within bounds. The immutability of the
525        //   data is also guaranteed by the safety requirements of the function.
526        // - `offset + count` can't overflow since it is smaller than `self.count` and we've checked
527        //   that `self.count` won't overflow early in the constructor.
528        Ok(unsafe { core::slice::from_raw_parts_mut(self.cpu_addr.add(offset), count) })
529    }
530
531    /// Writes data to the region starting from `offset`. `offset` is in units of `T`, not the
532    /// number of bytes.
533    ///
534    /// # Safety
535    ///
536    /// * Callers must ensure that the device does not read/write to/from memory while the returned
537    ///   slice is live.
538    /// * Callers must ensure that this call does not race with a read or write to the same region
539    ///   that overlaps with this write.
540    ///
541    /// # Examples
542    ///
543    /// ```
544    /// # fn test(alloc: &mut kernel::dma::CoherentAllocation<u8>) -> Result {
545    /// let somedata: [u8; 4] = [0xf; 4];
546    /// let buf: &[u8] = &somedata;
547    /// // SAFETY: There is no concurrent HW operation on the device and no other R/W access to the
548    /// // region.
549    /// unsafe { alloc.write(buf, 0)?; }
550    /// # Ok::<(), Error>(()) }
551    /// ```
552    pub unsafe fn write(&mut self, src: &[T], offset: usize) -> Result {
553        self.validate_range(offset, src.len())?;
554        // SAFETY:
555        // - The pointer is valid due to type invariant on `CoherentAllocation`
556        //   and we've just checked that the range and index is within bounds.
557        // - `offset + count` can't overflow since it is smaller than `self.count` and we've checked
558        //   that `self.count` won't overflow early in the constructor.
559        unsafe {
560            core::ptr::copy_nonoverlapping(src.as_ptr(), self.cpu_addr.add(offset), src.len())
561        };
562        Ok(())
563    }
564
565    /// Returns a pointer to an element from the region with bounds checking. `offset` is in
566    /// units of `T`, not the number of bytes.
567    ///
568    /// Public but hidden since it should only be used from [`dma_read`] and [`dma_write`] macros.
569    #[doc(hidden)]
570    pub fn item_from_index(&self, offset: usize) -> Result<*mut T> {
571        if offset >= self.count {
572            return Err(EINVAL);
573        }
574        // SAFETY:
575        // - The pointer is valid due to type invariant on `CoherentAllocation`
576        // and we've just checked that the range and index is within bounds.
577        // - `offset` can't overflow since it is smaller than `self.count` and we've checked
578        // that `self.count` won't overflow early in the constructor.
579        Ok(unsafe { self.cpu_addr.add(offset) })
580    }
581
582    /// Reads the value of `field` and ensures that its type is [`FromBytes`].
583    ///
584    /// # Safety
585    ///
586    /// This must be called from the [`dma_read`] macro which ensures that the `field` pointer is
587    /// validated beforehand.
588    ///
589    /// Public but hidden since it should only be used from [`dma_read`] macro.
590    #[doc(hidden)]
591    pub unsafe fn field_read<F: FromBytes>(&self, field: *const F) -> F {
592        // SAFETY:
593        // - By the safety requirements field is valid.
594        // - Using read_volatile() here is not sound as per the usual rules, the usage here is
595        // a special exception with the following notes in place. When dealing with a potential
596        // race from a hardware or code outside kernel (e.g. user-space program), we need that
597        // read on a valid memory is not UB. Currently read_volatile() is used for this, and the
598        // rationale behind is that it should generate the same code as READ_ONCE() which the
599        // kernel already relies on to avoid UB on data races. Note that the usage of
600        // read_volatile() is limited to this particular case, it cannot be used to prevent
601        // the UB caused by racing between two kernel functions nor do they provide atomicity.
602        unsafe { field.read_volatile() }
603    }
604
605    /// Writes a value to `field` and ensures that its type is [`AsBytes`].
606    ///
607    /// # Safety
608    ///
609    /// This must be called from the [`dma_write`] macro which ensures that the `field` pointer is
610    /// validated beforehand.
611    ///
612    /// Public but hidden since it should only be used from [`dma_write`] macro.
613    #[doc(hidden)]
614    pub unsafe fn field_write<F: AsBytes>(&self, field: *mut F, val: F) {
615        // SAFETY:
616        // - By the safety requirements field is valid.
617        // - Using write_volatile() here is not sound as per the usual rules, the usage here is
618        // a special exception with the following notes in place. When dealing with a potential
619        // race from a hardware or code outside kernel (e.g. user-space program), we need that
620        // write on a valid memory is not UB. Currently write_volatile() is used for this, and the
621        // rationale behind is that it should generate the same code as WRITE_ONCE() which the
622        // kernel already relies on to avoid UB on data races. Note that the usage of
623        // write_volatile() is limited to this particular case, it cannot be used to prevent
624        // the UB caused by racing between two kernel functions nor do they provide atomicity.
625        unsafe { field.write_volatile(val) }
626    }
627}
628
629/// Note that the device configured to do DMA must be halted before this object is dropped.
630impl<T: AsBytes + FromBytes> Drop for CoherentAllocation<T> {
631    fn drop(&mut self) {
632        let size = self.count * core::mem::size_of::<T>();
633        // SAFETY: Device pointer is guaranteed as valid by the type invariant on `Device`.
634        // The cpu address, and the dma handle are valid due to the type invariants on
635        // `CoherentAllocation`.
636        unsafe {
637            bindings::dma_free_attrs(
638                self.dev.as_raw(),
639                size,
640                self.cpu_addr.cast(),
641                self.dma_handle,
642                self.dma_attrs.as_raw(),
643            )
644        }
645    }
646}
647
648// SAFETY: It is safe to send a `CoherentAllocation` to another thread if `T`
649// can be sent to another thread.
650unsafe impl<T: AsBytes + FromBytes + Send> Send for CoherentAllocation<T> {}
651
652/// Reads a field of an item from an allocated region of structs.
653///
654/// # Examples
655///
656/// ```
657/// use kernel::device::Device;
658/// use kernel::dma::{attrs::*, CoherentAllocation};
659///
660/// struct MyStruct { field: u32, }
661///
662/// // SAFETY: All bit patterns are acceptable values for `MyStruct`.
663/// unsafe impl kernel::transmute::FromBytes for MyStruct{};
664/// // SAFETY: Instances of `MyStruct` have no uninitialized portions.
665/// unsafe impl kernel::transmute::AsBytes for MyStruct{};
666///
667/// # fn test(alloc: &kernel::dma::CoherentAllocation<MyStruct>) -> Result {
668/// let whole = kernel::dma_read!(alloc[2]);
669/// let field = kernel::dma_read!(alloc[1].field);
670/// # Ok::<(), Error>(()) }
671/// ```
672#[macro_export]
673macro_rules! dma_read {
674    ($dma:expr, $idx: expr, $($field:tt)*) => {{
675        (|| -> ::core::result::Result<_, $crate::error::Error> {
676            let item = $crate::dma::CoherentAllocation::item_from_index(&$dma, $idx)?;
677            // SAFETY: `item_from_index` ensures that `item` is always a valid pointer and can be
678            // dereferenced. The compiler also further validates the expression on whether `field`
679            // is a member of `item` when expanded by the macro.
680            unsafe {
681                let ptr_field = ::core::ptr::addr_of!((*item) $($field)*);
682                ::core::result::Result::Ok(
683                    $crate::dma::CoherentAllocation::field_read(&$dma, ptr_field)
684                )
685            }
686        })()
687    }};
688    ($dma:ident [ $idx:expr ] $($field:tt)* ) => {
689        $crate::dma_read!($dma, $idx, $($field)*)
690    };
691    ($($dma:ident).* [ $idx:expr ] $($field:tt)* ) => {
692        $crate::dma_read!($($dma).*, $idx, $($field)*)
693    };
694}
695
696/// Writes to a field of an item from an allocated region of structs.
697///
698/// # Examples
699///
700/// ```
701/// use kernel::device::Device;
702/// use kernel::dma::{attrs::*, CoherentAllocation};
703///
704/// struct MyStruct { member: u32, }
705///
706/// // SAFETY: All bit patterns are acceptable values for `MyStruct`.
707/// unsafe impl kernel::transmute::FromBytes for MyStruct{};
708/// // SAFETY: Instances of `MyStruct` have no uninitialized portions.
709/// unsafe impl kernel::transmute::AsBytes for MyStruct{};
710///
711/// # fn test(alloc: &kernel::dma::CoherentAllocation<MyStruct>) -> Result {
712/// kernel::dma_write!(alloc[2].member = 0xf);
713/// kernel::dma_write!(alloc[1] = MyStruct { member: 0xf });
714/// # Ok::<(), Error>(()) }
715/// ```
716#[macro_export]
717macro_rules! dma_write {
718    ($dma:ident [ $idx:expr ] $($field:tt)*) => {{
719        $crate::dma_write!($dma, $idx, $($field)*)
720    }};
721    ($($dma:ident).* [ $idx:expr ] $($field:tt)* ) => {{
722        $crate::dma_write!($($dma).*, $idx, $($field)*)
723    }};
724    ($dma:expr, $idx: expr, = $val:expr) => {
725        (|| -> ::core::result::Result<_, $crate::error::Error> {
726            let item = $crate::dma::CoherentAllocation::item_from_index(&$dma, $idx)?;
727            // SAFETY: `item_from_index` ensures that `item` is always a valid item.
728            unsafe { $crate::dma::CoherentAllocation::field_write(&$dma, item, $val) }
729            ::core::result::Result::Ok(())
730        })()
731    };
732    ($dma:expr, $idx: expr, $(.$field:ident)* = $val:expr) => {
733        (|| -> ::core::result::Result<_, $crate::error::Error> {
734            let item = $crate::dma::CoherentAllocation::item_from_index(&$dma, $idx)?;
735            // SAFETY: `item_from_index` ensures that `item` is always a valid pointer and can be
736            // dereferenced. The compiler also further validates the expression on whether `field`
737            // is a member of `item` when expanded by the macro.
738            unsafe {
739                let ptr_field = ::core::ptr::addr_of_mut!((*item) $(.$field)*);
740                $crate::dma::CoherentAllocation::field_write(&$dma, ptr_field, $val)
741            }
742            ::core::result::Result::Ok(())
743        })()
744    };
745}