bus: mhi: ep: Add support for interrupt moderation timer

MHI spec defines the interrupt moderation timer feature using which the
host can limit the number of interrupts being raised for an event ring by
the device. This feature allows the host to process multiple event ring
elements by a single IRQ from the device, thereby eliminating the need to
process IRQ for each element.

The INTMODT field in the event context array provides the value to be used
for delaying the IRQ generation from device. This value, along with the
Block Event Interrupt (BEI) flag of the TRE defines how IRQ is generated to
the host.

Support for interrupt moderation timer is implemented using delayed
workqueue in kernel. And a separate delayed work item is used for each
event ring.

Link: https://lore.kernel.org/r/20231026045513.12981-1-manivannan.sadhasivam@linaro.org
Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>

3 files changed, 40 insertions, 4 deletions

diff --git a/drivers/bus/mhi/ep/internal.h b/drivers/bus/mhi/ep/internal.h
index a2125fa5fe2f9..8c5cf2b679510 100644
--- a/drivers/bus/mhi/ep/internal.h
+++ b/drivers/bus/mhi/ep/internal.h
@@ -126,6 +126,7 @@ struct mhi_ep_ring {
 	union mhi_ep_ring_ctx *ring_ctx;
 	struct mhi_ring_element *ring_cache;
 	enum mhi_ep_ring_type type;
+	struct delayed_work intmodt_work;
 	u64 rbase;
 	size_t rd_offset;
 	size_t wr_offset;
@@ -135,7 +136,9 @@ struct mhi_ep_ring {
 	u32 ch_id;
 	u32 er_index;
 	u32 irq_vector;
+	u32 intmodt;
 	bool started;
+	bool irq_pending;
 };
 
 struct mhi_ep_cmd {
diff --git a/drivers/bus/mhi/ep/main.c b/drivers/bus/mhi/ep/main.c
index 517279600645f..c759183943eda 100644
--- a/drivers/bus/mhi/ep/main.c
+++ b/drivers/bus/mhi/ep/main.c
@@ -54,11 +54,27 @@ static int mhi_ep_send_event(struct mhi_ep_cntrl *mhi_cntrl, u32 ring_idx,
 	mutex_unlock(&mhi_cntrl->event_lock);
 
 	/*
-	 * Raise IRQ to host only if the BEI flag is not set in TRE. Host might
-	 * set this flag for interrupt moderation as per MHI protocol.
+	 * As per the MHI specification, section 4.3, Interrupt moderation:
+	 *
+	 * 1. If BEI flag is not set, cancel any pending intmodt work if started
+	 * for the event ring and raise IRQ immediately.
+	 *
+	 * 2. If both BEI and intmodt are set, and if no IRQ is pending for the
+	 * same event ring, start the IRQ delayed work as per the value of
+	 * intmodt. If previous IRQ is pending, then do nothing as the pending
+	 * IRQ is enough for the host to process the current event ring element.
+	 *
+	 * 3. If BEI is set and intmodt is not set, no need to raise IRQ.
 	 */
-	if (!bei)
+	if (!bei) {
+		if (READ_ONCE(ring->irq_pending))
+			cancel_delayed_work(&ring->intmodt_work);
+
 		mhi_cntrl->raise_irq(mhi_cntrl, ring->irq_vector);
+	} else if (ring->intmodt && !READ_ONCE(ring->irq_pending)) {
+		WRITE_ONCE(ring->irq_pending, true);
+		schedule_delayed_work(&ring->intmodt_work, msecs_to_jiffies(ring->intmodt));
+	}
 
 	return 0;
 
diff --git a/drivers/bus/mhi/ep/ring.c b/drivers/bus/mhi/ep/ring.c
index 115518ec76a43..a1071c13761b4 100644
--- a/drivers/bus/mhi/ep/ring.c
+++ b/drivers/bus/mhi/ep/ring.c
@@ -157,6 +157,15 @@ void mhi_ep_ring_init(struct mhi_ep_ring *ring, enum mhi_ep_ring_type type, u32
 	}
 }
 
+static void mhi_ep_raise_irq(struct work_struct *work)
+{
+	struct mhi_ep_ring *ring = container_of(work, struct mhi_ep_ring, intmodt_work.work);
+	struct mhi_ep_cntrl *mhi_cntrl = ring->mhi_cntrl;
+
+	mhi_cntrl->raise_irq(mhi_cntrl, ring->irq_vector);
+	WRITE_ONCE(ring->irq_pending, false);
+}
+
 int mhi_ep_ring_start(struct mhi_ep_cntrl *mhi_cntrl, struct mhi_ep_ring *ring,
 			union mhi_ep_ring_ctx *ctx)
 {
@@ -173,8 +182,13 @@ int mhi_ep_ring_start(struct mhi_ep_cntrl *mhi_cntrl, struct mhi_ep_ring *ring,
 	if (ring->type == RING_TYPE_CH)
 		ring->er_index = le32_to_cpu(ring->ring_ctx->ch.erindex);
 
-	if (ring->type == RING_TYPE_ER)
+	if (ring->type == RING_TYPE_ER) {
 		ring->irq_vector = le32_to_cpu(ring->ring_ctx->ev.msivec);
+		ring->intmodt = FIELD_GET(EV_CTX_INTMODT_MASK,
+					  le32_to_cpu(ring->ring_ctx->ev.intmod));
+
+		INIT_DELAYED_WORK(&ring->intmodt_work, mhi_ep_raise_irq);
+	}
 
 	/* During ring init, both rp and wp are equal */
 	memcpy_fromio(&val, (void __iomem *) &ring->ring_ctx->generic.rp, sizeof(u64));
@@ -201,6 +215,9 @@ int mhi_ep_ring_start(struct mhi_ep_cntrl *mhi_cntrl, struct mhi_ep_ring *ring,
 
 void mhi_ep_ring_reset(struct mhi_ep_cntrl *mhi_cntrl, struct mhi_ep_ring *ring)
 {
+	if (ring->type == RING_TYPE_ER)
+		cancel_delayed_work_sync(&ring->intmodt_work);
+
 	ring->started = false;
 	kfree(ring->ring_cache);
 	ring->ring_cache = NULL;