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>
---
v1 -> v2:
- Moved the spi changes as patch2.
drivers/spi/spi-geni-qcom.c | 7 +++++++
1 file changed, 7 insertions(+)
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)) {
--
2.17.1
