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| author |   Franklin S Cooper Jr <fcooper@ti.com> | 2016-06-27 09:54:08 -0500 |
|---|---|---|
| committer |   Mark Brown <broonie@kernel.org> | 2016-07-05 16:48:25 +0200 |
| commit | 4bd00413cde851d84b297c1b0dae15109025e84b (patch) | |
| tree | 9b4b411dd05c7dfa70dad52b2fb8147fca891e5a /drivers/spi | |
| parent | Linux 4.7-rc1 (diff) | |
| download | linux-dev-4bd00413cde851d84b297c1b0dae15109025e84b.tar.xz linux-dev-4bd00413cde851d84b297c1b0dae15109025e84b.zip | |
spi: omap2-mcspi: Add comments for RX only DMA buffer workaround
OMAP35x and OMAP37x mentions in the McSPI End-of-Transfer Sequences section
that if the McSPI is configured as a Master and only DMA RX is being
performed then the DMA transfer size needs to be reduced by 1 or 2.
This was originally implemented by:
commit 57c5c28dbc83 ("spi: omap2_mcspi rxdma bugfix")
This patch adds comments to clarify what is going on in the code since its
not obvious what problem its addressing.
Signed-off-by: Franklin S Cooper Jr <fcooper@ti.com>
Signed-off-by: Mark Brown <broonie@kernel.org>
Diffstat (limited to 'drivers/spi')
| -rw-r--r-- | drivers/spi/spi-omap2-mcspi.c | 13 |
1 files changed, 13 insertions, 0 deletions
diff --git a/drivers/spi/spi-omap2-mcspi.c b/drivers/spi/spi-omap2-mcspi.c index 1d237e93a289..c47f95879833 100644 --- a/drivers/spi/spi-omap2-mcspi.c +++ b/drivers/spi/spi-omap2-mcspi.c @@ -459,6 +459,11 @@ omap2_mcspi_rx_dma(struct spi_device *spi, struct spi_transfer *xfer, count = xfer->len; dma_count = xfer->len; + /* + * In the "End-of-Transfer Procedure" section for DMA RX in OMAP35x TRM + * it mentions reducing DMA transfer length by one element in master + * normal mode. + */ if (mcspi->fifo_depth == 0) dma_count -= es; @@ -478,6 +483,10 @@ omap2_mcspi_rx_dma(struct spi_device *spi, struct spi_transfer *xfer, dmaengine_slave_config(mcspi_dma->dma_rx, &cfg); + /* + * Reduce DMA transfer length by one more if McSPI is + * configured in turbo mode. + */ if ((l & OMAP2_MCSPI_CHCONF_TURBO) && mcspi->fifo_depth == 0) dma_count -= es; @@ -507,6 +516,10 @@ omap2_mcspi_rx_dma(struct spi_device *spi, struct spi_transfer *xfer, if (mcspi->fifo_depth > 0) return count; + /* + * Due to the DMA transfer length reduction the missing bytes must + * be read manually to receive all of the expected data. + */ omap2_mcspi_set_enable(spi, 0); elements = element_count - 1; |