spi: omap2-mcspi: Add comments for RX only DMA buffer workaround (4bd00413) · Commits · 戴 / test

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 ("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>

drivers/spi/spi-omap2-mcspi.c

+13 −0

Original line number	Diff line number	Diff line
		@@ -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;

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