Re: [PATCH v1 1/1] spi: spi-geni-qcom: Add immediate DMA support

[Dmitry Baryshkov <dmitry.baryshkov@xxxxxxxxxx>]

On Thu, Nov 28, 2024 at 07:06:22PM +0530, Jyothi Kumar Seerapu wrote:
> 
> 
> On 11/22/2024 3:38 AM, Dmitry Baryshkov wrote:
> > On Thu, Nov 21, 2024 at 05:22:01PM +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.
> > 
> > Is it supported on all GPI DMA platforms, starting from SDM845?
> Yes, it supported on all GPI DMA platforms.
> > 
> > > 
> > > 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@xxxxxxxxxxx>
> > > ---
> > >   drivers/dma/qcom/gpi.c           | 32 +++++++++++++++++++++++++++-----
> > >   drivers/spi/spi-geni-qcom.c      |  7 +++++++
> > >   include/linux/dma/qcom-gpi-dma.h |  7 +++++++
> > 
> > How is this supposed to be merged? Please try to separate the patches by
> > the subsystem, letting maintainers to handle possible dependencies.
> > 
> Sure, separated  the patches in V2.
> > >   3 files changed, 41 insertions(+), 5 deletions(-)
> > > 
> > > diff --git a/drivers/dma/qcom/gpi.c b/drivers/dma/qcom/gpi.c
> > > index 52a7c8f2498f..a8df1e835e27 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;
> > > +	u8 *buf;
> > > +	int len = 0;
> > >   	/* 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);
> > > +	/* Support Immediate dma for write transfers for data length up to 8 bytes */
> > > +	if ((spi->flags & QCOM_GPI_IMMEDIATE_DMA) && direction == DMA_MEM_TO_DEV) {
> > > +		buf = (u8 *)sg_virt(sgl);
> > > -	tre->dword[3] = u32_encode_bits(TRE_TYPE_DMA, TRE_FLAGS_TYPE);
> > > -	if (direction == DMA_MEM_TO_DEV)
> > > +		/* memcpy may not always be length of 8, hence pre-fill both dword's with 0 */
> > > +		tre->dword[0] = 0;
> > > +		tre->dword[1] = 0;
> > > +		memcpy((u8 *)&tre->dword[0], buf, len);
> > 
> > Drop all type conversions, they should not be necessary. memcpy()
> > functions accepts void pointers.
> Done
> > 
> > > +
> > > +		tre->dword[2] = u32_encode_bits(len, TRE_DMA_IMMEDIATE_LEN);
> > > +
> > > +		tre->dword[3] = u32_encode_bits(TRE_TYPE_DMA, TRE_FLAGS_TYPE);
> > >   		tre->dword[3] |= u32_encode_bits(1, TRE_FLAGS_IEOT);
> > > +		tre->dword[3] |= u32_encode_bits(1, TRE_FLAGS_IMMEDIATE_DMA);
> > > +	} 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);
> > > +	}
> > >   	for (i = 0; i < tre_idx; i++)
> > >   		dev_dbg(dev, "TRE:%d %x:%x:%x:%x\n", i, desc->tre[i].dword[0],
> > > diff --git a/drivers/spi/spi-geni-qcom.c b/drivers/spi/spi-geni-qcom.c
> > > index 768d7482102a..53c8f6b7f3c5 100644
> > > --- a/drivers/spi/spi-geni-qcom.c
> > > +++ b/drivers/spi/spi-geni-qcom.c
> > > @@ -472,11 +472,18 @@ static int setup_gsi_xfer(struct spi_transfer *xfer, struct spi_geni_master *mas
> > >   		mas->cur_speed_hz = xfer->speed_hz;
> > >   	}
> > > +	/*
> > > +	 * Set QCOM_GPI_IMMEDIATE_DMA flag if transfer length up to 8 bytes.
> > > +	 */
> > >   	if (xfer->tx_buf && xfer->rx_buf) {
> > >   		peripheral.cmd = SPI_DUPLEX;
> > > +		if (xfer->len <= QCOM_GPI_IMMEDIATE_DMA_LEN)
> > > +			peripheral.flags |= QCOM_GPI_IMMEDIATE_DMA;
> > >   	} else if (xfer->tx_buf) {
> > >   		peripheral.cmd = SPI_TX;
> > >   		peripheral.rx_len = 0;
> > > +		if (xfer->len <= QCOM_GPI_IMMEDIATE_DMA_LEN)
> > > +			peripheral.flags |= QCOM_GPI_IMMEDIATE_DMA;
> > >   	} else if (xfer->rx_buf) {
> > >   		peripheral.cmd = SPI_RX;
> > >   		if (!(mas->cur_bits_per_word % MIN_WORD_LEN)) {
> > > diff --git a/include/linux/dma/qcom-gpi-dma.h b/include/linux/dma/qcom-gpi-dma.h
> > > index 6680dd1a43c6..0eb96e62a1f1 100644
> > > --- a/include/linux/dma/qcom-gpi-dma.h
> > > +++ b/include/linux/dma/qcom-gpi-dma.h
> > > @@ -15,6 +15,11 @@ enum spi_transfer_cmd {
> > >   	SPI_DUPLEX,
> > >   };
> > > +#define QCOM_GPI_BLOCK_EVENT_IRQ	BIT(0)
> > 
> > Unrelated, please drop.
> Sure, done.
> > 
> > > +#define QCOM_GPI_IMMEDIATE_DMA		BIT(1)
> > 
> > Can GPI driver deduce whether it should use immediate DMA based on the
> > transfer length?
> protocol driver like SPI will update whether it should use immediate DMA or
> not based on the transfer length and GPI driver will configure it
> accordingly .

You are describing your implementation. I asked if it is possible to be
implemented other way around. Otherwise you are adding too much
knowledge to the SPI driver.

> > 
> > > +
> > > +#define QCOM_GPI_IMMEDIATE_DMA_LEN	8
> > > +
> > >   /**
> > >    * struct gpi_spi_config - spi config for peripheral
> > >    *
> > > @@ -30,6 +35,7 @@ enum spi_transfer_cmd {
> > >    * @cs: chip select toggle
> > >    * @set_config: set peripheral config
> > >    * @rx_len: receive length for buffer
> > > + * @flags: flags for immediate dma and block event interrupt support
> > >    */
> > >   struct gpi_spi_config {
> > >   	u8 set_config;
> > > @@ -44,6 +50,7 @@ struct gpi_spi_config {
> > >   	u32 clk_src;
> > >   	enum spi_transfer_cmd cmd;
> > >   	u32 rx_len;
> > > +	u8 flags;
> > >   };
> > >   enum i2c_op {
> > > -- 
> > > 2.17.1
> > > 
> > 

-- 
With best wishes
Dmitry