On 12/4/2024 7:09 PM, Dmitry Baryshkov wrote:
On Wed, 4 Dec 2024 at 15:25, Jyothi Kumar Seerapu
<quic_jseerapu@xxxxxxxxxxx> wrote:
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@xxxxxxxxxxx>
---
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@xxxxxxxxxxx/
https://lore.kernel.org/all/20241128133351.24593-3-quic_jseerapu@xxxxxxxxxxx/
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@xxxxxxxxxxx/
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]);
I was suggesting to _inline_ this condition rather than having a
separate variable for it.
I can directly use the condition as follows:
if (direction == DMA_MEM_TO_DEV && len <= 2 * sizeof(tre->dword[0]))
However, this condition also needs to account for the
"TRE_FLAGS_IMMEDIATE_DMA" update. Therefore, I introduced a separate
variable.
tre->dword[3] |= u32_encode_bits(!!immediate_dma, TRE_FLAGS_IMMEDIATE_DMA);
Please let me know if it's acceptable to mention the entire condition in
both places instead of using a separate variable.
+
+ /* 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
