linux-kernel - Re: [PATCH v6 1/2] dmaengine: qcom: gpi: Add GPI Block event interrupt support

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Message-ID: <ze5y6llgo2qx4nvilaqcmkam5ywqa76d6uetn34iblz4nefpeu@ozbgzwbyd54u>
Date: Tue, 6 May 2025 14:32:29 +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 v6 1/2] dmaengine: qcom: gpi: Add GPI Block event
 interrupt support

On Tue, May 06, 2025 at 04:48:43PM +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.
> 
> When using BEI, consider splitting a single multi-message transfer into
> chunks of 8 messages internally and so interrupts are not expected for
> the first 7 message completions, only the last message triggers
> an interrupt, indicating the completion of 8 messages.
> 
> This BEI mechanism enhances overall transfer efficiency.
> 
> Signed-off-by: Jyothi Kumar Seerapu <quic_jseerapu@...cinc.com>
> ---
> 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           | 3 +++
>  include/linux/dma/qcom-gpi-dma.h | 2 ++
>  2 files changed, 5 insertions(+)
> 
> diff --git a/drivers/dma/qcom/gpi.c b/drivers/dma/qcom/gpi.c
> index b1f0001cc99c..7e511f54166a 100644
> --- a/drivers/dma/qcom/gpi.c
> +++ b/drivers/dma/qcom/gpi.c
> @@ -1695,6 +1695,9 @@ 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 (!(i2c->dma_flags & DMA_PREP_INTERRUPT))
> +			tre->dword[3] |= u32_encode_bits(1, TRE_FLAGS_BEI);
>  	}
>  
>  	for (i = 0; i < tre_idx; i++)
> diff --git a/include/linux/dma/qcom-gpi-dma.h b/include/linux/dma/qcom-gpi-dma.h
> index 6680dd1a43c6..ebac0d3edff2 100644
> --- a/include/linux/dma/qcom-gpi-dma.h
> +++ b/include/linux/dma/qcom-gpi-dma.h
> @@ -65,6 +65,7 @@ enum i2c_op {
>   * @rx_len: receive length for buffer
>   * @op: i2c cmd
>   * @muli-msg: is part of multi i2c r-w msgs
> + * @dma_flags: Flags indicating DMA capabilities
>   */
>  struct gpi_i2c_config {
>  	u8 set_config;
> @@ -78,6 +79,7 @@ struct gpi_i2c_config {
>  	u32 rx_len;
>  	enum i2c_op op;
>  	bool multi_msg;
> +	unsigned int dma_flags;

Why do you need extra field instead of using
dma_async_tx_descriptor.flags?

>  };
>  
>  #endif /* QCOM_GPI_DMA_H */
> -- 
> 2.17.1
> 

-- 
With best wishes
Dmitry