Re: [PATCH v3] dmaengine: qcom: gpi: Add GPI immediate DMA support for SPI protocol

[Jyothi Kumar Seerapu <quic_jseerapu@quicinc.com>]

On 12/4/2024 6:15 PM, Dmitry Baryshkov wrote:
> On Wed, Dec 04, 2024 at 05:50:59PM +0530, Jyothi Kumar Seerapu wrote:
>> The DMA TRE(Transfer ring element) buffer contains the DMA
>> buffer address. Accessing data from this address can cause
>> significant delays in SPI transfers, which can be mitigated to
>> some extent by utilizing immediate DMA support.
>>
>> QCOM GPI DMA hardware supports an immediate DMA feature for data
>> up to 8 bytes, storing the data directly in the DMA TRE buffer
>> instead of the DMA buffer address. This enhancement enables faster
>> SPI data transfers.
>>
>> This optimization reduces the average transfer time from 25 us to
>> 16 us for a single SPI transfer of 8 bytes length, with a clock
>> frequency of 50 MHz.
>>
>> Signed-off-by: Jyothi Kumar Seerapu <quic_jseerapu@quicinc.com>
>> ---
>>
>> v2-> v3:
>>     - When to enable Immediate DMA support, control is moved to GPI driver
>>       from SPI driver.
>>     - Optimizations are done in GPI driver related to immediate dma changes.
>>     - Removed the immediate dma supported changes in qcom-gpi-dma.h file
>>       and handled in GPI driver.
>>
>>     Link to v2:
>> 	https://lore.kernel.org/all/20241128133351.24593-2-quic_jseerapu@quicinc.com/
>> 	https://lore.kernel.org/all/20241128133351.24593-3-quic_jseerapu@quicinc.com/
>>
>> v1 -> v2:
>>     - Separated the patches to dmaengine and spi subsystems
>>     - Removed the changes which are not required for this feature from
>>       qcom-gpi-dma.h file.
>>     - Removed the type conversions used in gpi_create_spi_tre.
>>    
>>     Link to v1:
>> 	https://lore.kernel.org/lkml/20241121115201.2191-2-quic_jseerapu@quicinc.com/
>>
>>   drivers/dma/qcom/gpi.c | 32 +++++++++++++++++++++++++++-----
>>   1 file changed, 27 insertions(+), 5 deletions(-)
>>
>> diff --git a/drivers/dma/qcom/gpi.c b/drivers/dma/qcom/gpi.c
>> index 52a7c8f2498f..35451d5a81f7 100644
>> --- a/drivers/dma/qcom/gpi.c
>> +++ b/drivers/dma/qcom/gpi.c
>> @@ -27,6 +27,7 @@
>>   #define TRE_FLAGS_IEOT		BIT(9)
>>   #define TRE_FLAGS_BEI		BIT(10)
>>   #define TRE_FLAGS_LINK		BIT(11)
>> +#define TRE_FLAGS_IMMEDIATE_DMA	BIT(16)
>>   #define TRE_FLAGS_TYPE		GENMASK(23, 16)
>>   
>>   /* SPI CONFIG0 WD0 */
>> @@ -64,6 +65,7 @@
>>   
>>   /* DMA TRE */
>>   #define TRE_DMA_LEN		GENMASK(23, 0)
>> +#define TRE_DMA_IMMEDIATE_LEN	GENMASK(3, 0)
>>   
>>   /* Register offsets from gpi-top */
>>   #define GPII_n_CH_k_CNTXT_0_OFFS(n, k)	(0x20000 + (0x4000 * (n)) + (0x80 * (k)))
>> @@ -1711,6 +1713,8 @@ static int gpi_create_spi_tre(struct gchan *chan, struct gpi_desc *desc,
>>   	dma_addr_t address;
>>   	struct gpi_tre *tre;
>>   	unsigned int i;
>> +	int len;
>> +	u8 immediate_dma;
>>   
>>   	/* first create config tre if applicable */
>>   	if (direction == DMA_MEM_TO_DEV && spi->set_config) {
>> @@ -1763,14 +1767,32 @@ static int gpi_create_spi_tre(struct gchan *chan, struct gpi_desc *desc,
>>   	tre_idx++;
>>   
>>   	address = sg_dma_address(sgl);
>> -	tre->dword[0] = lower_32_bits(address);
>> -	tre->dword[1] = upper_32_bits(address);
>> +	len = sg_dma_len(sgl);
>>   
>> -	tre->dword[2] = u32_encode_bits(sg_dma_len(sgl), TRE_DMA_LEN);
>> +	immediate_dma = (direction == DMA_MEM_TO_DEV) && len <= 2 * sizeof(tre->dword[0]);
> 
> inline this condition, remove extra brackets and split the line after &&.
Hi Dmitry Baryshkov, thanks for the review.
Sure, i will make the changes mentioned below. Please let me know otherwise.

immediate_dma = direction == DMA_MEM_TO_DEV &&
                 len <= 2 * sizeof(tre->dword[0]);>
>> +
>> +	/* Support Immediate dma for write transfers for data length up to 8 bytes */
>> +	if (immediate_dma) {
>> +		/*
>> +		 * For Immediate dma, data length may not always be length of 8 bytes,
>> +		 * it can be length less than 8, hence initialize both dword's with 0
>> +		 */
>> +		tre->dword[0] = 0;
>> +		tre->dword[1] = 0;
>> +		memcpy(&tre->dword[0], sg_virt(sgl), len);
>> +
>> +		tre->dword[2] = u32_encode_bits(len, TRE_DMA_IMMEDIATE_LEN);
>> +	} else {
>> +		tre->dword[0] = lower_32_bits(address);
>> +		tre->dword[1] = upper_32_bits(address);
>> +
>> +		tre->dword[2] = u32_encode_bits(len, TRE_DMA_LEN);
>> +	}
>>   
>>   	tre->dword[3] = u32_encode_bits(TRE_TYPE_DMA, TRE_FLAGS_TYPE);
>> -	if (direction == DMA_MEM_TO_DEV)
>> -		tre->dword[3] |= u32_encode_bits(1, TRE_FLAGS_IEOT);
>> +	tre->dword[3] |= u32_encode_bits(!!immediate_dma, TRE_FLAGS_IMMEDIATE_DMA);
>> +	tre->dword[3] |= u32_encode_bits(!!(direction == DMA_MEM_TO_DEV),
>> +					 TRE_FLAGS_IEOT);
>>   
>>   	for (i = 0; i < tre_idx; i++)
>>   		dev_dbg(dev, "TRE:%d %x:%x:%x:%x\n", i, desc->tre[i].dword[0],
>> -- 
>> 2.17.1
>>
>