Unverified Commit f3530f26 authored by Patrice Chotard's avatar Patrice Chotard Committed by Mark Brown
Browse files

spi: stm32-qspi: Trigger DMA only if more than 4 bytes to transfer 



In order to optimize accesses to spi flashes, trigger a DMA only
if more than 4 bytes has to be transferred.

DMA transfer preparation's cost becomes negligible above 4 bytes to
transfer. Below this threshold, indirect transfer give more throughput.

mtd_speedtest shows that page write throughtput increases :
  - from 779 to 853 KiB/s (~9.5%) with s25fl512s SPI-NOR.
  - from 5283 to 5666 KiB/s (~7.25%) with Micron SPI-NAND.

Signed-off-by: default avatarChristophe Kerello <christophe.kerello@foss.st.com>
Signed-off-by: default avatarPatrice Chotard <patrice.chotard@foss.st.com>
Link: https://lore.kernel.org/r/20210419121541.11617-3-patrice.chotard@foss.st.com


Signed-off-by: default avatarMark Brown <broonie@kernel.org>
parent 102e9d19

drivers/spi/spi-stm32-qspi.c

+3 −2
Original line number Diff line number Diff line
@@ -269,8 +269,9 @@ static int stm32_qspi_tx(struct stm32_qspi *qspi, const struct spi_mem_op *op) 


	if (qspi->fmode == CCR_FMODE_MM)

		return stm32_qspi_tx_mm(qspi, op);

	else if ((op->data.dir == SPI_MEM_DATA_IN && qspi->dma_chrx) ||

		 (op->data.dir == SPI_MEM_DATA_OUT && qspi->dma_chtx))

	else if (((op->data.dir == SPI_MEM_DATA_IN && qspi->dma_chrx) ||

		 (op->data.dir == SPI_MEM_DATA_OUT && qspi->dma_chtx)) &&

		  op->data.nbytes > 4)

		if (!stm32_qspi_tx_dma(qspi, op))

			return 0;