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
