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

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Message-ID: <xy2jgnearfsoln7tmjbb7l6zuwm7sq74wohsxj77eeval5wig5@kisng4ufgbuo>
Date: Wed, 3 Sep 2025 12:25:37 +0300
From: Dmitry Baryshkov <dmitry.baryshkov@....qualcomm.com>
To: Jyothi Kumar Seerapu <quic_jseerapu@...cinc.com>
Cc: 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>,
        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: Re: [PATCH v7 1/2] dmaengine: qcom: gpi: Add GPI Block event
 interrupt support

On Wed, Sep 03, 2025 at 01:00:58PM +0530, Jyothi Kumar Seerapu wrote:
> 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.

Duplicate phrase.

> 
> 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;

Comment in the source file.

> +
>  	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
> 

-- 
With best wishes
Dmitry