Commit 4bd00413 authored by Franklin S Cooper Jr's avatar Franklin S Cooper Jr Committed by Mark Brown
Browse files

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 57c5c28d ("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: default avatarFranklin S Cooper Jr <fcooper@ti.com>
Signed-off-by: default avatarMark Brown <broonie@kernel.org>
parent 1a695a90

drivers/spi/spi-omap2-mcspi.c

+13 −0
Original line number Original line Diff line number Diff line
@@ -459,6 +459,11 @@ omap2_mcspi_rx_dma(struct spi_device *spi, struct spi_transfer *xfer, 
	count = xfer->len;

	count = xfer->len;

	dma_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)

	if (mcspi->fifo_depth == 0)

		dma_count -= es;

		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);

		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)

		if ((l & OMAP2_MCSPI_CHCONF_TURBO) && mcspi->fifo_depth == 0)

			dma_count -= es;

			dma_count -= es;
@@ -507,6 +516,10 @@ omap2_mcspi_rx_dma(struct spi_device *spi, struct spi_transfer *xfer, 
	if (mcspi->fifo_depth > 0)

	if (mcspi->fifo_depth > 0)

		return count;

		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);

	omap2_mcspi_set_enable(spi, 0);





	elements = element_count - 1;

	elements = element_count - 1;

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