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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: Christophe Kerello <christophe.kerello@foss.st.com>
Signed-off-by: Patrice Chotard <patrice.chotard@foss.st.com>
Link: https://lore.kernel.org/r/20210419121541.11617-3-patrice.chotard@foss.st.com
Signed-off-by: Mark Brown <broonie@kernel.org>
This commit is contained in:
Patrice Chotard 2021-04-19 14:15:40 +02:00 committed by Mark Brown
parent 102e9d1936
commit f3530f26f8
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GPG Key ID: 24D68B725D5487D0
1 changed files with 3 additions and 2 deletions
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5
drivers/spi/spi-stm32-qspi.c
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@ -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;