€•ê{      Œsphinx.addnodes”Œdocument”“”)”}”(Œ	rawsource”Œ ”Œchildren”]”(Œtranslations”ŒLanguagesNode”“”)”}”(hhh]”(h Œpending_xref”“”)”}”(hhh]”Œdocutils.nodes”ŒText”“”ŒChinese (Simplified)”…””}”Œparent”hsbaŒ
attributes”}”(Œids”]”Œclasses”]”Œnames”]”Œdupnames”]”Œbackrefs”]”Œ	refdomain”Œstd”Œreftype”Œdoc”Œ	reftarget”Œ%/translations/zh_CN/i2c/dev-interface”Œmodname”NŒ	classname”NŒrefexplicit”ˆuŒtagname”hhhubh)”}”(hhh]”hŒChinese (Traditional)”…””}”hh2sbah}”(h]”h ]”h"]”h$]”h&]”Œ	refdomain”h)Œreftype”h+Œ	reftarget”Œ%/translations/zh_TW/i2c/dev-interface”Œmodname”NŒ	classname”NŒrefexplicit”ˆuh1hhhubh)”}”(hhh]”hŒItalian”…””}”hhFsbah}”(h]”h ]”h"]”h$]”h&]”Œ	refdomain”h)Œreftype”h+Œ	reftarget”Œ%/translations/it_IT/i2c/dev-interface”Œmodname”NŒ	classname”NŒrefexplicit”ˆuh1hhhubh)”}”(hhh]”hŒJapanese”…””}”hhZsbah}”(h]”h ]”h"]”h$]”h&]”Œ	refdomain”h)Œreftype”h+Œ	reftarget”Œ%/translations/ja_JP/i2c/dev-interface”Œmodname”NŒ	classname”NŒrefexplicit”ˆuh1hhhubh)”}”(hhh]”hŒKorean”…””}”hhnsbah}”(h]”h ]”h"]”h$]”h&]”Œ	refdomain”h)Œreftype”h+Œ	reftarget”Œ%/translations/ko_KR/i2c/dev-interface”Œmodname”NŒ	classname”NŒrefexplicit”ˆuh1hhhubh)”}”(hhh]”hŒSpanish”…””}”hh‚sbah}”(h]”h ]”h"]”h$]”h&]”Œ	refdomain”h)Œreftype”h+Œ	reftarget”Œ%/translations/sp_SP/i2c/dev-interface”Œmodname”NŒ	classname”NŒrefexplicit”ˆuh1hhhubeh}”(h]”h ]”h"]”h$]”h&]”Œcurrent_language”ŒEnglish”uh1h
hhŒ	_document”hŒsource”NŒline”NubhŒsection”“”)”}”(hhh]”(hŒtitle”“”)”}”(hŒ,Implementing I2C device drivers in userspace”h]”hŒ,Implementing I2C device drivers in userspace”…””}”(hh¨hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h¦hh£hžhhŸŒ?/var/lib/git/docbuild/linux/Documentation/i2c/dev-interface.rst”h KubhŒ	paragraph”“”)”}”(hŒÉUsually, I2C devices are controlled by a kernel driver. But it is also
possible to access all devices on an adapter from userspace, through
the /dev interface. You need to load module i2c-dev for this.”h]”hŒÉUsually, I2C devices are controlled by a kernel driver. But it is also
possible to access all devices on an adapter from userspace, through
the /dev interface. You need to load module i2c-dev for this.”…””}”(hh¹hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h Khh£hžhubh¸)”}”(hX=  Each registered I2C adapter gets a number, counting from 0. You can
examine /sys/class/i2c-dev/ to see what number corresponds to which adapter.
Alternatively, you can run "i2cdetect -l" to obtain a formatted list of all
I2C adapters present on your system at a given time. i2cdetect is part of
the i2c-tools package.”h]”hXA  Each registered I2C adapter gets a number, counting from 0. You can
examine /sys/class/i2c-dev/ to see what number corresponds to which adapter.
Alternatively, you can run â€œi2cdetect -lâ€ to obtain a formatted list of all
I2C adapters present on your system at a given time. i2cdetect is part of
the i2c-tools package.”…””}”(hhÇhžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h K	hh£hžhubh¸)”}”(hX  I2C device files are character device files with major device number 89
and a minor device number corresponding to the number assigned as
explained above. They should be called "i2c-%d" (i2c-0, i2c-1, ...,
i2c-10, ...). All 256 minor device numbers are reserved for I2C.”h]”hX  I2C device files are character device files with major device number 89
and a minor device number corresponding to the number assigned as
explained above. They should be called â€œi2c-%dâ€ (i2c-0, i2c-1, ...,
i2c-10, ...). All 256 minor device numbers are reserved for I2C.”…””}”(hhÕhžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h Khh£hžhubh¢)”}”(hhh]”(h§)”}”(hŒ	C example”h]”hŒ	C example”…””}”(hhæhžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h¦hhãhžhhŸh¶h Kubh¸)”}”(hŒoSo let's say you want to access an I2C adapter from a C program.
First, you need to include these two headers::”h]”hŒpSo letâ€™s say you want to access an I2C adapter from a C program.
First, you need to include these two headers:”…””}”(hhôhžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h KhhãhžhubhŒliteral_block”“”)”}”(hŒ1#include <linux/i2c-dev.h>
#include <i2c/smbus.h>”h]”hŒ1#include <linux/i2c-dev.h>
#include <i2c/smbus.h>”…””}”hj  sbah}”(h]”h ]”h"]”h$]”h&]”Œ	xml:space”Œpreserve”uh1j  hŸh¶h Khhãhžhubh¸)”}”(hX  Now, you have to decide which adapter you want to access. You should
inspect /sys/class/i2c-dev/ or run "i2cdetect -l" to decide this.
Adapter numbers are assigned somewhat dynamically, so you can not
assume much about them. They can even change from one boot to the next.”h]”hX  Now, you have to decide which adapter you want to access. You should
inspect /sys/class/i2c-dev/ or run â€œi2cdetect -lâ€ to decide this.
Adapter numbers are assigned somewhat dynamically, so you can not
assume much about them. They can even change from one boot to the next.”…””}”(hj  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h Khhãhžhubh¸)”}”(hŒ.Next thing, open the device file, as follows::”h]”hŒ-Next thing, open the device file, as follows:”…””}”(hj"  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h K#hhãhžhubj  )”}”(hX	  int file;
int adapter_nr = 2; /* probably dynamically determined */
char filename[20];

snprintf(filename, 19, "/dev/i2c-%d", adapter_nr);
file = open(filename, O_RDWR);
if (file < 0) {
  /* ERROR HANDLING; you can check errno to see what went wrong */
  exit(1);
}”h]”hX	  int file;
int adapter_nr = 2; /* probably dynamically determined */
char filename[20];

snprintf(filename, 19, "/dev/i2c-%d", adapter_nr);
file = open(filename, O_RDWR);
if (file < 0) {
  /* ERROR HANDLING; you can check errno to see what went wrong */
  exit(1);
}”…””}”hj0  sbah}”(h]”h ]”h"]”h$]”h&]”j  j  uh1j  hŸh¶h K%hhãhžhubh¸)”}”(hŒdWhen you have opened the device, you must specify with what device
address you want to communicate::”h]”hŒcWhen you have opened the device, you must specify with what device
address you want to communicate:”…””}”(hj>  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h K0hhãhžhubj  )”}”(hŒŸint addr = 0x40; /* The I2C address */

if (ioctl(file, I2C_SLAVE, addr) < 0) {
  /* ERROR HANDLING; you can check errno to see what went wrong */
  exit(1);
}”h]”hŒŸint addr = 0x40; /* The I2C address */

if (ioctl(file, I2C_SLAVE, addr) < 0) {
  /* ERROR HANDLING; you can check errno to see what went wrong */
  exit(1);
}”…””}”hjL  sbah}”(h]”h ]”h"]”h$]”h&]”j  j  uh1j  hŸh¶h K3hhãhžhubh¸)”}”(hŒÁWell, you are all set up now. You can now use SMBus commands or plain
I2C to communicate with your device. SMBus commands are preferred if
the device supports them. Both are illustrated below::”h]”hŒÀWell, you are all set up now. You can now use SMBus commands or plain
I2C to communicate with your device. SMBus commands are preferred if
the device supports them. Both are illustrated below:”…””}”(hjZ  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h K:hhãhžhubj  )”}”(hX‘  __u8 reg = 0x10; /* Device register to access */
__s32 res;
char buf[10];

/* Using SMBus commands */
res = i2c_smbus_read_word_data(file, reg);
if (res < 0) {
  /* ERROR HANDLING: I2C transaction failed */
} else {
  /* res contains the read word */
}

/*
 * Using I2C Write, equivalent of
 * i2c_smbus_write_word_data(file, reg, 0x6543)
 */
buf[0] = reg;
buf[1] = 0x43;
buf[2] = 0x65;
if (write(file, buf, 3) != 3) {
  /* ERROR HANDLING: I2C transaction failed */
}

/* Using I2C Read, equivalent of i2c_smbus_read_byte(file) */
if (read(file, buf, 1) != 1) {
  /* ERROR HANDLING: I2C transaction failed */
} else {
  /* buf[0] contains the read byte */
}”h]”hX‘  __u8 reg = 0x10; /* Device register to access */
__s32 res;
char buf[10];

/* Using SMBus commands */
res = i2c_smbus_read_word_data(file, reg);
if (res < 0) {
  /* ERROR HANDLING: I2C transaction failed */
} else {
  /* res contains the read word */
}

/*
 * Using I2C Write, equivalent of
 * i2c_smbus_write_word_data(file, reg, 0x6543)
 */
buf[0] = reg;
buf[1] = 0x43;
buf[2] = 0x65;
if (write(file, buf, 3) != 3) {
  /* ERROR HANDLING: I2C transaction failed */
}

/* Using I2C Read, equivalent of i2c_smbus_read_byte(file) */
if (read(file, buf, 1) != 1) {
  /* ERROR HANDLING: I2C transaction failed */
} else {
  /* buf[0] contains the read byte */
}”…””}”hjh  sbah}”(h]”h ]”h"]”h$]”h&]”j  j  uh1j  hŸh¶h K>hhãhžhubh¸)”}”(hX7  Note that only a subset of the I2C and SMBus protocols can be achieved by
the means of read() and write() calls. In particular, so-called combined
transactions (mixing read and write messages in the same transaction)
aren't supported. For this reason, this interface is almost never used by
user-space programs.”h]”hX9  Note that only a subset of the I2C and SMBus protocols can be achieved by
the means of read() and write() calls. In particular, so-called combined
transactions (mixing read and write messages in the same transaction)
arenâ€™t supported. For this reason, this interface is almost never used by
user-space programs.”…””}”(hjv  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h K\hhãhžhubh¸)”}”(hŒzIMPORTANT: because of the use of inline functions, you *have* to use
'-O' or some variation when you compile your program!”h]”(hŒ7IMPORTANT: because of the use of inline functions, you ”…””}”(hj„  hžhhŸNh NubhŒemphasis”“”)”}”(hŒ*have*”h]”hŒhave”…””}”(hjŽ  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1jŒ  hj„  ubhŒA to use
â€˜-Oâ€™ or some variation when you compile your program!”…””}”(hj„  hžhhŸNh Nubeh}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h Kbhhãhžhubeh}”(h]”Œ	c-example”ah ]”h"]”Œ	c example”ah$]”h&]”uh1h¡hh£hžhhŸh¶h Kubh¢)”}”(hhh]”(h§)”}”(hŒFull interface description”h]”hŒFull interface description”…””}”(hj±  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h¦hj®  hžhhŸh¶h Kgubh¸)”}”(hŒ!The following IOCTLs are defined:”h]”hŒ!The following IOCTLs are defined:”…””}”(hj¿  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h Kihj®  hžhubhŒdefinition_list”“”)”}”(hhh]”(hŒdefinition_list_item”“”)”}”(hŒ¿``ioctl(file, I2C_SLAVE, long addr)``
Change slave address. The address is passed in the 7 lower bits of the
argument (except for 10 bit addresses, passed in the 10 lower bits in this
case).
”h]”(hŒterm”“”)”}”(hŒ%``ioctl(file, I2C_SLAVE, long addr)``”h]”hŒliteral”“”)”}”(hjÜ  h]”hŒ!ioctl(file, I2C_SLAVE, long addr)”…””}”(hjà  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1jÞ  hjÚ  ubah}”(h]”h ]”h"]”h$]”h&]”uh1jØ  hŸh¶h KnhjÔ  ubhŒ
definition”“”)”}”(hhh]”h¸)”}”(hŒ˜Change slave address. The address is passed in the 7 lower bits of the
argument (except for 10 bit addresses, passed in the 10 lower bits in this
case).”h]”hŒ˜Change slave address. The address is passed in the 7 lower bits of the
argument (except for 10 bit addresses, passed in the 10 lower bits in this
case).”…””}”(hjø  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h Klhjõ  ubah}”(h]”h ]”h"]”h$]”h&]”uh1jó  hjÔ  ubeh}”(h]”h ]”h"]”h$]”h&]”uh1jÒ  hŸh¶h KnhjÏ  ubjÓ  )”}”(hŒÝ``ioctl(file, I2C_TENBIT, long select)``
Selects ten bit addresses if select not equals 0, selects normal 7 bit
addresses if select equals 0. Default 0.  This request is only valid
if the adapter has I2C_FUNC_10BIT_ADDR.
”h]”(jÙ  )”}”(hŒ(``ioctl(file, I2C_TENBIT, long select)``”h]”jß  )”}”(hj  h]”hŒ$ioctl(file, I2C_TENBIT, long select)”…””}”(hj  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1jÞ  hj  ubah}”(h]”h ]”h"]”h$]”h&]”uh1jØ  hŸh¶h Kshj  ubjô  )”}”(hhh]”h¸)”}”(hŒ³Selects ten bit addresses if select not equals 0, selects normal 7 bit
addresses if select equals 0. Default 0.  This request is only valid
if the adapter has I2C_FUNC_10BIT_ADDR.”h]”hŒ³Selects ten bit addresses if select not equals 0, selects normal 7 bit
addresses if select equals 0. Default 0.  This request is only valid
if the adapter has I2C_FUNC_10BIT_ADDR.”…””}”(hj0  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h Kqhj-  ubah}”(h]”h ]”h"]”h$]”h&]”uh1jó  hj  ubeh}”(h]”h ]”h"]”h$]”h&]”uh1jÒ  hŸh¶h KshjÏ  hžhubjÓ  )”}”(hXT  ``ioctl(file, I2C_PEC, long select)``
Selects SMBus PEC (packet error checking) generation and verification
if select not equals 0, disables if select equals 0. Default 0.
Used only for SMBus transactions.  This request only has an effect if the
the adapter has I2C_FUNC_SMBUS_PEC; it is still safe if not, it just
doesn't have any effect.
”h]”(jÙ  )”}”(hŒ%``ioctl(file, I2C_PEC, long select)``”h]”jß  )”}”(hjP  h]”hŒ!ioctl(file, I2C_PEC, long select)”…””}”(hjR  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1jÞ  hjN  ubah}”(h]”h ]”h"]”h$]”h&]”uh1jØ  hŸh¶h KzhjJ  ubjô  )”}”(hhh]”h¸)”}”(hX-  Selects SMBus PEC (packet error checking) generation and verification
if select not equals 0, disables if select equals 0. Default 0.
Used only for SMBus transactions.  This request only has an effect if the
the adapter has I2C_FUNC_SMBUS_PEC; it is still safe if not, it just
doesn't have any effect.”h]”hX/  Selects SMBus PEC (packet error checking) generation and verification
if select not equals 0, disables if select equals 0. Default 0.
Used only for SMBus transactions.  This request only has an effect if the
the adapter has I2C_FUNC_SMBUS_PEC; it is still safe if not, it just
doesnâ€™t have any effect.”…””}”(hjh  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h Kvhje  ubah}”(h]”h ]”h"]”h$]”h&]”uh1jó  hjJ  ubeh}”(h]”h ]”h"]”h$]”h&]”uh1jÒ  hŸh¶h KzhjÏ  hžhubjÓ  )”}”(hŒk``ioctl(file, I2C_FUNCS, unsigned long *funcs)``
Gets the adapter functionality and puts it in ``*funcs``.
”h]”(jÙ  )”}”(hŒ0``ioctl(file, I2C_FUNCS, unsigned long *funcs)``”h]”jß  )”}”(hjˆ  h]”hŒ,ioctl(file, I2C_FUNCS, unsigned long *funcs)”…””}”(hjŠ  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1jÞ  hj†  ubah}”(h]”h ]”h"]”h$]”h&]”uh1jØ  hŸh¶h K}hj‚  ubjô  )”}”(hhh]”h¸)”}”(hŒ9Gets the adapter functionality and puts it in ``*funcs``.”h]”(hŒ.Gets the adapter functionality and puts it in ”…””}”(hj   hžhhŸNh Nubjß  )”}”(hŒ
``*funcs``”h]”hŒ*funcs”…””}”(hj¨  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1jÞ  hj   ubhŒ.”…””}”(hj   hžhhŸNh Nubeh}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h K}hj  ubah}”(h]”h ]”h"]”h$]”h&]”uh1jó  hj‚  ubeh}”(h]”h ]”h"]”h$]”h&]”uh1jÒ  hŸh¶h K}hjÏ  hžhubjÓ  )”}”(hXÆ  ``ioctl(file, I2C_RDWR, struct i2c_rdwr_ioctl_data *msgset)``
Do combined read/write transaction without stop in between.
Only valid if the adapter has I2C_FUNC_I2C.  The argument is
a pointer to a::

  struct i2c_rdwr_ioctl_data {
    struct i2c_msg *msgs;  /* ptr to array of simple messages */
    int nmsgs;             /* number of messages to exchange */
  }

The msgs[] themselves contain further pointers into data buffers.
The function will write or read data to or from that buffers depending
on whether the I2C_M_RD flag is set in a particular message or not.
The slave address and whether to use ten bit address mode has to be
set in each message, overriding the values set with the above ioctl's.
”h]”(jÙ  )”}”(hŒ=``ioctl(file, I2C_RDWR, struct i2c_rdwr_ioctl_data *msgset)``”h]”jß  )”}”(hjÒ  h]”hŒ9ioctl(file, I2C_RDWR, struct i2c_rdwr_ioctl_data *msgset)”…””}”(hjÔ  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1jÞ  hjÐ  ubah}”(h]”h ]”h"]”h$]”h&]”uh1jØ  hŸh¶h KhjÌ  ubjô  )”}”(hhh]”(h¸)”}”(hŒ‰Do combined read/write transaction without stop in between.
Only valid if the adapter has I2C_FUNC_I2C.  The argument is
a pointer to a::”h]”hŒˆDo combined read/write transaction without stop in between.
Only valid if the adapter has I2C_FUNC_I2C.  The argument is
a pointer to a:”…””}”(hjê  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h K€hjç  ubj  )”}”(hŒ›struct i2c_rdwr_ioctl_data {
  struct i2c_msg *msgs;  /* ptr to array of simple messages */
  int nmsgs;             /* number of messages to exchange */
}”h]”hŒ›struct i2c_rdwr_ioctl_data {
  struct i2c_msg *msgs;  /* ptr to array of simple messages */
  int nmsgs;             /* number of messages to exchange */
}”…””}”hjø  sbah}”(h]”h ]”h"]”h$]”h&]”j  j  uh1j  hŸh¶h K„hjç  ubh¸)”}”(hXW  The msgs[] themselves contain further pointers into data buffers.
The function will write or read data to or from that buffers depending
on whether the I2C_M_RD flag is set in a particular message or not.
The slave address and whether to use ten bit address mode has to be
set in each message, overriding the values set with the above ioctl's.”h]”hXY  The msgs[] themselves contain further pointers into data buffers.
The function will write or read data to or from that buffers depending
on whether the I2C_M_RD flag is set in a particular message or not.
The slave address and whether to use ten bit address mode has to be
set in each message, overriding the values set with the above ioctlâ€™s.”…””}”(hj  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h K‰hjç  ubeh}”(h]”h ]”h"]”h$]”h&]”uh1jó  hjÌ  ubeh}”(h]”h ]”h"]”h$]”h&]”uh1jÒ  hŸh¶h KhjÏ  hžhubjÓ  )”}”(hŒ¦``ioctl(file, I2C_SMBUS, struct i2c_smbus_ioctl_data *args)``
If possible, use the provided ``i2c_smbus_*`` methods described below instead
of issuing direct ioctls.
”h]”(jÙ  )”}”(hŒ=``ioctl(file, I2C_SMBUS, struct i2c_smbus_ioctl_data *args)``”h]”jß  )”}”(hj&  h]”hŒ9ioctl(file, I2C_SMBUS, struct i2c_smbus_ioctl_data *args)”…””}”(hj(  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1jÞ  hj$  ubah}”(h]”h ]”h"]”h$]”h&]”uh1jØ  hŸh¶h K‘hj   ubjô  )”}”(hhh]”h¸)”}”(hŒgIf possible, use the provided ``i2c_smbus_*`` methods described below instead
of issuing direct ioctls.”h]”(hŒIf possible, use the provided ”…””}”(hj>  hžhhŸNh Nubjß  )”}”(hŒ``i2c_smbus_*``”h]”hŒi2c_smbus_*”…””}”(hjF  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1jÞ  hj>  ubhŒ: methods described below instead
of issuing direct ioctls.”…””}”(hj>  hžhhŸNh Nubeh}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h Khj;  ubah}”(h]”h ]”h"]”h$]”h&]”uh1jó  hj   ubeh}”(h]”h ]”h"]”h$]”h&]”uh1jÒ  hŸh¶h K‘hjÏ  hžhubeh}”(h]”h ]”h"]”h$]”h&]”uh1jÍ  hj®  hžhhŸh¶h Nubh¸)”}”(hŒ½You can do plain I2C transactions by using read(2) and write(2) calls.
You do not need to pass the address byte; instead, set it through
ioctl I2C_SLAVE before you try to access the device.”h]”hŒ½You can do plain I2C transactions by using read(2) and write(2) calls.
You do not need to pass the address byte; instead, set it through
ioctl I2C_SLAVE before you try to access the device.”…””}”(hjp  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h K“hj®  hžhubh¸)”}”(hŒ}You can do SMBus level transactions (see documentation file smbus-protocol.rst
for details) through the following functions::”h]”hŒ|You can do SMBus level transactions (see documentation file smbus-protocol.rst
for details) through the following functions:”…””}”(hj~  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h K—hj®  hžhubj  )”}”(hXþ  __s32 i2c_smbus_write_quick(int file, __u8 value);
__s32 i2c_smbus_read_byte(int file);
__s32 i2c_smbus_write_byte(int file, __u8 value);
__s32 i2c_smbus_read_byte_data(int file, __u8 command);
__s32 i2c_smbus_write_byte_data(int file, __u8 command, __u8 value);
__s32 i2c_smbus_read_word_data(int file, __u8 command);
__s32 i2c_smbus_write_word_data(int file, __u8 command, __u16 value);
__s32 i2c_smbus_process_call(int file, __u8 command, __u16 value);
__s32 i2c_smbus_block_process_call(int file, __u8 command, __u8 length,
                                   __u8 *values);
__s32 i2c_smbus_read_block_data(int file, __u8 command, __u8 *values);
__s32 i2c_smbus_write_block_data(int file, __u8 command, __u8 length,
                                 __u8 *values);”h]”hXþ  __s32 i2c_smbus_write_quick(int file, __u8 value);
__s32 i2c_smbus_read_byte(int file);
__s32 i2c_smbus_write_byte(int file, __u8 value);
__s32 i2c_smbus_read_byte_data(int file, __u8 command);
__s32 i2c_smbus_write_byte_data(int file, __u8 command, __u8 value);
__s32 i2c_smbus_read_word_data(int file, __u8 command);
__s32 i2c_smbus_write_word_data(int file, __u8 command, __u16 value);
__s32 i2c_smbus_process_call(int file, __u8 command, __u16 value);
__s32 i2c_smbus_block_process_call(int file, __u8 command, __u8 length,
                                   __u8 *values);
__s32 i2c_smbus_read_block_data(int file, __u8 command, __u8 *values);
__s32 i2c_smbus_write_block_data(int file, __u8 command, __u8 length,
                                 __u8 *values);”…””}”hjŒ  sbah}”(h]”h ]”h"]”h$]”h&]”j  j  uh1j  hŸh¶h Kšhj®  hžhubh¸)”}”(hX&  All these transactions return -1 on failure; you can read errno to see
what happened. The 'write' transactions return 0 on success; the
'read' transactions return the read value, except for read_block, which
returns the number of values read. The block buffers need not be longer
than 32 bytes.”h]”hX.  All these transactions return -1 on failure; you can read errno to see
what happened. The â€˜writeâ€™ transactions return 0 on success; the
â€˜readâ€™ transactions return the read value, except for read_block, which
returns the number of values read. The block buffers need not be longer
than 32 bytes.”…””}”(hjš  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h K¨hj®  hžhubh¸)”}”(hŒ¾The above functions are made available by linking against the libi2c library,
which is provided by the i2c-tools project.  See:
https://git.kernel.org/pub/scm/utils/i2c-tools/i2c-tools.git/.”h]”(hŒ€The above functions are made available by linking against the libi2c library,
which is provided by the i2c-tools project.  See:
”…””}”(hj¨  hžhhŸNh NubhŒ	reference”“”)”}”(hŒ=https://git.kernel.org/pub/scm/utils/i2c-tools/i2c-tools.git/”h]”hŒ=https://git.kernel.org/pub/scm/utils/i2c-tools/i2c-tools.git/”…””}”(hj²  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”Œrefuri”j´  uh1j°  hj¨  ubhŒ.”…””}”(hj¨  hžhhŸNh Nubeh}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h K®hj®  hžhubeh}”(h]”Œfull-interface-description”ah ]”h"]”Œfull interface description”ah$]”h&]”uh1h¡hh£hžhhŸh¶h Kgubh¢)”}”(hhh]”(h§)”}”(hŒImplementation details”h]”hŒImplementation details”…””}”(hjÖ  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h¦hjÓ  hžhhŸh¶h K´ubh¸)”}”(hŒpFor the interested, here's the code flow which happens inside the kernel
when you use the /dev interface to I2C:”h]”hŒrFor the interested, hereâ€™s the code flow which happens inside the kernel
when you use the /dev interface to I2C:”…””}”(hjä  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h K¶hjÓ  hžhubhŒenumerated_list”“”)”}”(hhh]”(hŒ	list_item”“”)”}”(hŒbYour program opens /dev/i2c-N and calls ioctl() on it, as described in
section "C example" above.
”h]”h¸)”}”(hŒaYour program opens /dev/i2c-N and calls ioctl() on it, as described in
section "C example" above.”h]”hŒeYour program opens /dev/i2c-N and calls ioctl() on it, as described in
section â€œC exampleâ€ above.”…””}”(hjý  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h K¹hjù  ubah}”(h]”h ]”h"]”h$]”h&]”uh1j÷  hjô  hžhhŸh¶h Nubjø  )”}”(hŒïThese open() and ioctl() calls are handled by the i2c-dev kernel
driver: see i2c-dev.c:i2cdev_open() and i2c-dev.c:i2cdev_ioctl(),
respectively. You can think of i2c-dev as a generic I2C chip driver
that can be programmed from user-space.
”h]”h¸)”}”(hŒîThese open() and ioctl() calls are handled by the i2c-dev kernel
driver: see i2c-dev.c:i2cdev_open() and i2c-dev.c:i2cdev_ioctl(),
respectively. You can think of i2c-dev as a generic I2C chip driver
that can be programmed from user-space.”h]”hŒîThese open() and ioctl() calls are handled by the i2c-dev kernel
driver: see i2c-dev.c:i2cdev_open() and i2c-dev.c:i2cdev_ioctl(),
respectively. You can think of i2c-dev as a generic I2C chip driver
that can be programmed from user-space.”…””}”(hj  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h K¼hj  ubah}”(h]”h ]”h"]”h$]”h&]”uh1j÷  hjô  hžhhŸh¶h Nubjø  )”}”(hŒðSome ioctl() calls are for administrative tasks and are handled by
i2c-dev directly. Examples include I2C_SLAVE (set the address of the
device you want to access) and I2C_PEC (enable or disable SMBus error
checking on future transactions.)
”h]”h¸)”}”(hŒïSome ioctl() calls are for administrative tasks and are handled by
i2c-dev directly. Examples include I2C_SLAVE (set the address of the
device you want to access) and I2C_PEC (enable or disable SMBus error
checking on future transactions.)”h]”hŒïSome ioctl() calls are for administrative tasks and are handled by
i2c-dev directly. Examples include I2C_SLAVE (set the address of the
device you want to access) and I2C_PEC (enable or disable SMBus error
checking on future transactions.)”…””}”(hj-  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h KÁhj)  ubah}”(h]”h ]”h"]”h$]”h&]”uh1j÷  hjô  hžhhŸh¶h Nubjø  )”}”(hXŸ  Other ioctl() calls are converted to in-kernel function calls by
i2c-dev. Examples include I2C_FUNCS, which queries the I2C adapter
functionality using i2c.h:i2c_get_functionality(), and I2C_SMBUS, which
performs an SMBus transaction using i2c-core-smbus.c:i2c_smbus_xfer().

The i2c-dev driver is responsible for checking all the parameters that
come from user-space for validity. After this point, there is no
difference between these calls that came from user-space through i2c-dev
and calls that would have been performed by kernel I2C chip drivers
directly. This means that I2C bus drivers don't need to implement
anything special to support access from user-space.
”h]”(h¸)”}”(hX  Other ioctl() calls are converted to in-kernel function calls by
i2c-dev. Examples include I2C_FUNCS, which queries the I2C adapter
functionality using i2c.h:i2c_get_functionality(), and I2C_SMBUS, which
performs an SMBus transaction using i2c-core-smbus.c:i2c_smbus_xfer().”h]”hX  Other ioctl() calls are converted to in-kernel function calls by
i2c-dev. Examples include I2C_FUNCS, which queries the I2C adapter
functionality using i2c.h:i2c_get_functionality(), and I2C_SMBUS, which
performs an SMBus transaction using i2c-core-smbus.c:i2c_smbus_xfer().”…””}”(hjE  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h KÆhjA  ubh¸)”}”(hXŠ  The i2c-dev driver is responsible for checking all the parameters that
come from user-space for validity. After this point, there is no
difference between these calls that came from user-space through i2c-dev
and calls that would have been performed by kernel I2C chip drivers
directly. This means that I2C bus drivers don't need to implement
anything special to support access from user-space.”h]”hXŒ  The i2c-dev driver is responsible for checking all the parameters that
come from user-space for validity. After this point, there is no
difference between these calls that came from user-space through i2c-dev
and calls that would have been performed by kernel I2C chip drivers
directly. This means that I2C bus drivers donâ€™t need to implement
anything special to support access from user-space.”…””}”(hjS  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h KËhjA  ubeh}”(h]”h ]”h"]”h$]”h&]”uh1j÷  hjô  hžhhŸh¶h Nubjø  )”}”(hXÀ  These i2c.h functions are wrappers to the actual implementation of
your I2C bus driver. Each adapter must declare callback functions
implementing these standard calls. i2c.h:i2c_get_functionality() calls
i2c_adapter.algo->functionality(), while
i2c-core-smbus.c:i2c_smbus_xfer() calls either
adapter.algo->smbus_xfer() if it is implemented, or if not,
i2c-core-smbus.c:i2c_smbus_xfer_emulated() which in turn calls
i2c_adapter.algo->master_xfer().
”h]”h¸)”}”(hX¿  These i2c.h functions are wrappers to the actual implementation of
your I2C bus driver. Each adapter must declare callback functions
implementing these standard calls. i2c.h:i2c_get_functionality() calls
i2c_adapter.algo->functionality(), while
i2c-core-smbus.c:i2c_smbus_xfer() calls either
adapter.algo->smbus_xfer() if it is implemented, or if not,
i2c-core-smbus.c:i2c_smbus_xfer_emulated() which in turn calls
i2c_adapter.algo->master_xfer().”h]”hX¿  These i2c.h functions are wrappers to the actual implementation of
your I2C bus driver. Each adapter must declare callback functions
implementing these standard calls. i2c.h:i2c_get_functionality() calls
i2c_adapter.algo->functionality(), while
i2c-core-smbus.c:i2c_smbus_xfer() calls either
adapter.algo->smbus_xfer() if it is implemented, or if not,
i2c-core-smbus.c:i2c_smbus_xfer_emulated() which in turn calls
i2c_adapter.algo->master_xfer().”…””}”(hjk  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h KÒhjg  ubah}”(h]”h ]”h"]”h$]”h&]”uh1j÷  hjô  hžhhŸh¶h Nubeh}”(h]”h ]”h"]”h$]”h&]”Œenumtype”Œarabic”Œprefix”hŒsuffix”Œ)”uh1jò  hjÓ  hžhhŸh¶h K¹ubh¸)”}”(hŒÓAfter your I2C bus driver has processed these requests, execution runs
up the call chain, with almost no processing done, except by i2c-dev to
package the returned data, if any, in suitable format for the ioctl.”h]”hŒÓAfter your I2C bus driver has processed these requests, execution runs
up the call chain, with almost no processing done, except by i2c-dev to
package the returned data, if any, in suitable format for the ioctl.”…””}”(hjŠ  hžhhŸNh Nubah}”(h]”h ]”h"]”h$]”h&]”uh1h·hŸh¶h KÛhjÓ  hžhubeh}”(h]”Œimplementation-details”ah ]”h"]”Œimplementation details”ah$]”h&]”uh1h¡hh£hžhhŸh¶h K´ubeh}”(h]”Œ,implementing-i2c-device-drivers-in-userspace”ah ]”h"]”Œ,implementing i2c device drivers in userspace”ah$]”h&]”uh1h¡hhhžhhŸh¶h Kubeh}”(h]”h ]”h"]”h$]”h&]”Œsource”h¶uh1hŒcurrent_source”NŒcurrent_line”NŒsettings”Œdocutils.frontend”ŒValues”“”)”}”(h¦NŒ	generator”NŒ	datestamp”NŒsource_link”NŒ
source_url”NŒtoc_backlinks”Œentry”Œfootnote_backlinks”KŒsectnum_xform”KŒstrip_comments”NŒstrip_elements_with_classes”NŒstrip_classes”NŒreport_level”KŒ
halt_level”KŒexit_status_level”KŒdebug”NŒwarning_stream”NŒ	traceback”ˆŒinput_encoding”Œ	utf-8-sig”Œinput_encoding_error_handler”Œstrict”Œoutput_encoding”Œutf-8”Œoutput_encoding_error_handler”jË  Œerror_encoding”Œutf-8”Œerror_encoding_error_handler”Œbackslashreplace”Œlanguage_code”Œen”Œrecord_dependencies”NŒconfig”NŒ	id_prefix”hŒauto_id_prefix”Œid”Œdump_settings”NŒdump_internals”NŒdump_transforms”NŒdump_pseudo_xml”NŒexpose_internals”NŒstrict_visitor”NŒ_disable_config”NŒ_source”h¶Œ_destination”NŒ_config_files”]”Œ7/var/lib/git/docbuild/linux/Documentation/docutils.conf”aŒfile_insertion_enabled”ˆŒraw_enabled”KŒline_length_limit”M'Œpep_references”NŒpep_base_url”Œhttps://peps.python.org/”Œpep_file_url_template”Œpep-%04d”Œrfc_references”NŒrfc_base_url”Œ&https://datatracker.ietf.org/doc/html/”Œ	tab_width”KŒtrim_footnote_reference_space”‰Œsyntax_highlight”Œlong”Œsmart_quotes”ˆŒsmartquotes_locales”]”Œcharacter_level_inline_markup”‰Œdoctitle_xform”‰Œdocinfo_xform”KŒsectsubtitle_xform”‰Œimage_loading”Œlink”Œembed_stylesheet”‰Œcloak_email_addresses”ˆŒsection_self_link”‰Œenv”NubŒreporter”NŒindirect_targets”]”Œsubstitution_defs”}”Œsubstitution_names”}”Œrefnames”}”Œrefids”}”Œnameids”}”(j¥  j¢  j«  j¨  jÐ  jÍ  j  jš  uŒ	nametypes”}”(j¥  ‰j«  ‰jÐ  ‰j  ‰uh}”(j¢  h£j¨  hãjÍ  j®  jš  jÓ  uŒfootnote_refs”}”Œcitation_refs”}”Œautofootnotes”]”Œautofootnote_refs”]”Œsymbol_footnotes”]”Œsymbol_footnote_refs”]”Œ	footnotes”]”Œ	citations”]”Œautofootnote_start”KŒsymbol_footnote_start”K Œ
id_counter”Œcollections”ŒCounter”“”}”…”R”Œparse_messages”]”Œtransform_messages”]”Œtransformer”NŒinclude_log”]”Œ
decoration”Nhžhub.