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

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Message-ID: <4456d0e2-3451-4749-acda-3b75ae99e89b@quicinc.com>
Date: Fri, 9 May 2025 11:48:44 +0530
From: Jyothi Kumar Seerapu <quic_jseerapu@...cinc.com>
To: Dmitry Baryshkov <dmitry.baryshkov@....qualcomm.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 5/6/2025 5:02 PM, Dmitry Baryshkov wrote:
> 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?

In the original I2C QCOM GENI driver, using the local variable (unsigned 
in flags) and updating the "DMA_PREP_INTERRUPT" flag.

Sure, i will review if "dma_async_tx_descriptor.flags" can be retrieved 
in GPI driver for DMA_PREP_INTERRUPT flag status.
> 
>>   };
>>   
>>   #endif /* QCOM_GPI_DMA_H */
>> -- 
>> 2.17.1
>>
>