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.


Jyothi Kumar Seerapu (1):
  spi: spi-geni-qcom: Add immediate DMA support

 drivers/dma/qcom/gpi.c           | 32 +++++++++++++++++++++++++++-----
 drivers/spi/spi-geni-qcom.c      |  7 +++++++
 include/linux/dma/qcom-gpi-dma.h |  7 +++++++
 3 files changed, 41 insertions(+), 5 deletions(-)

-- 
2.17.1

On Thu, Nov 21, 2024 at 05:22:00PM +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.

Please don't send cover letters for single patches, if there is anything
that needs saying put it in the changelog of the patch or after the ---
if it's administrative stuff.  This reduces mail volume and ensures that 
any important information is recorded in the changelog rather than being
lost.