linux-kernel - [PATCH v7 1/2] dmaengine: qcom: gpi: Add GPI Block event interrupt support

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Message-ID: <20250903073059.2151837-2-quic_jseerapu@quicinc.com>
Date: Wed, 3 Sep 2025 13:00:58 +0530
From: Jyothi Kumar Seerapu <quic_jseerapu@...cinc.com>
To: Vinod Koul <vkoul@...nel.org>,
        Mukesh Kumar Savaliya
	<quic_msavaliy@...cinc.com>,
        Viken Dadhaniya <quic_vdadhani@...cinc.com>,
        Andi Shyti <andi.shyti@...nel.org>,
        Sumit Semwal <sumit.semwal@...aro.org>,
        Christian König <christian.koenig@....com>
CC: <linux-arm-msm@...r.kernel.org>, <dmaengine@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, <linux-i2c@...r.kernel.org>,
        <linux-media@...r.kernel.org>, <dri-devel@...ts.freedesktop.org>,
        <linaro-mm-sig@...ts.linaro.org>, <quic_vtanuku@...cinc.com>
Subject: [PATCH v7 1/2] dmaengine: qcom: gpi: Add GPI Block event interrupt support

GSI hardware generates an interrupt for each transfer completion.
For multiple messages within a single transfer, this results in
N interrupts for N messages, leading to significant software
interrupt latency.

To mitigate this latency, utilize Block Event Interrupt (BEI) mechanism.
Enabling BEI instructs the GSI hardware to prevent interrupt generation
and BEI is disabled when an interrupt is necessary.

Large I2C transfer can be divided into chunks of messages internally.
Interrupts are not expected for the messages for which BEI bit set,
only the last message triggers an interrupt, indicating the completion of
N messages. This BEI mechanism enhances overall transfer efficiency.

This BEI mechanism enhances overall transfer efficiency.

Signed-off-by: Jyothi Kumar Seerapu <quic_jseerapu@...cinc.com>
---

v6 -> v7:
   - The design has been modified to configure BEI for interrupt
     generation either:
     After the last I2C message, if sufficient TREs are available, or
     After a specific I2C message, when no further TREs are available.
   - In the GPI driver, passed the flags argumnetr to the gpi_create_i2c_tre function
     and so avoided using external variables for DMA_PREP_INTERRUPT status.

v5 ->v6:
  - For updating the block event interrupt bit, instead of relying on
    bei_flag, decision check is moved with DMA_PREP_INTERRUPT flag.

v4 -> v5:
  - BEI flag naming changed from flags to bei_flag.
  - QCOM_GPI_BLOCK_EVENT_IRQ macro is removed from qcom-gpi-dma.h
    file, and Block event interrupt support is checked with bei_flag.

v3 -> v4:
  - API's added for Block event interrupt with multi descriptor support for
    I2C is moved from qcom-gpi-dma.h file to I2C geni qcom driver file.
  - gpi_multi_xfer_timeout_handler function is moved from GPI driver to
    I2C driver.

v2-> v3:
   - Renamed gpi_multi_desc_process to gpi_multi_xfer_timeout_handler
   - MIN_NUM_OF_MSGS_MULTI_DESC changed from 4 to 2
   - Added documentation for newly added changes in "qcom-gpi-dma.h" file
   - Updated commit description.

v1 -> v2:
   - Changed dma_addr type from array of pointers to array.
   - To support BEI functionality with the TRE size of 64 defined in GPI driver,
     updated QCOM_GPI_MAX_NUM_MSGS to 16 and NUM_MSGS_PER_IRQ to 4.

 drivers/dma/qcom/gpi.c | 11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/drivers/dma/qcom/gpi.c b/drivers/dma/qcom/gpi.c
index 8e87738086b2..66bfea1f156d 100644
--- a/drivers/dma/qcom/gpi.c
+++ b/drivers/dma/qcom/gpi.c
@@ -1619,7 +1619,8 @@ gpi_peripheral_config(struct dma_chan *chan, struct dma_slave_config *config)
 }
 
 static int gpi_create_i2c_tre(struct gchan *chan, struct gpi_desc *desc,
-			      struct scatterlist *sgl, enum dma_transfer_direction direction)
+			      struct scatterlist *sgl, enum dma_transfer_direction direction,
+			      unsigned long flags)
 {
 	struct gpi_i2c_config *i2c = chan->config;
 	struct device *dev = chan->gpii->gpi_dev->dev;
@@ -1684,6 +1685,9 @@ static int gpi_create_i2c_tre(struct gchan *chan, struct gpi_desc *desc,
 
 		tre->dword[3] = u32_encode_bits(TRE_TYPE_DMA, TRE_FLAGS_TYPE);
 		tre->dword[3] |= u32_encode_bits(1, TRE_FLAGS_IEOT);
+
+		if (!(flags & DMA_PREP_INTERRUPT))
+			tre->dword[3] |= u32_encode_bits(1, TRE_FLAGS_BEI);
 	}
 
 	for (i = 0; i < tre_idx; i++)
@@ -1827,6 +1831,9 @@ gpi_prep_slave_sg(struct dma_chan *chan, struct scatterlist *sgl,
 		return NULL;
 	}
 
+	if (!(flags & DMA_PREP_INTERRUPT) && (nr - nr_tre < 2))
+		return NULL;
+
 	gpi_desc = kzalloc(sizeof(*gpi_desc), GFP_NOWAIT);
 	if (!gpi_desc)
 		return NULL;
@@ -1835,7 +1842,7 @@ gpi_prep_slave_sg(struct dma_chan *chan, struct scatterlist *sgl,
 	if (gchan->protocol == QCOM_GPI_SPI) {
 		i = gpi_create_spi_tre(gchan, gpi_desc, sgl, direction);
 	} else if (gchan->protocol == QCOM_GPI_I2C) {
-		i = gpi_create_i2c_tre(gchan, gpi_desc, sgl, direction);
+		i = gpi_create_i2c_tre(gchan, gpi_desc, sgl, direction, flags);
 	} else {
 		dev_err(dev, "invalid peripheral: %d\n", gchan->protocol);
 		kfree(gpi_desc);
-- 
2.34.1