spi/pxa2xx: Prevent DMA from transferring too many bytes (111e0a9d) · Commits · 戴 / test

In case we are doing DMA transfer and the size of the buffer is not multiple of 4 bytes the driver truncates that to 4-byte boundary and tries to handle remaining bytes using PIO. Or that is what it tried to do. What actually happens is that it calls ALIGN() to the buffer size which aligns it to the next 4-byte boundary (doesn't truncate). Doing this results 1-3 bytes extra to be transferred. Furthermore we handle remaining bytes using PIO which results one extra byte to be transferred. In worst case the driver transfers 4 extra bytes. While investigating this it turned out that the DMA hardware doesn't even have such limitation so we can solve this by dropping the code that tries to handle unaligned bytes. Reported-by:

Chiau Ee Chew <chiau.ee.chew@intel.com> Reported-by:

Hock Leong Kweh <hock.leong.kweh@intel.com> Signed-off-by:

Mika Westerberg <mika.westerberg@linux.intel.com> Signed-off-by:

Mark Brown <broonie@linaro.org>

drivers/spi/spi-pxa2xx-dma.c

+0 −16

Original line number	Diff line number	Diff line
		@@ -29,18 +29,6 @@ static int pxa2xx_spi_map_dma_buffer(struct driver_data *drv_data,
		struct sg_table *sgt;
		void buf, pbuf;

		/*
		* Some DMA controllers have problems transferring buffers that are
		* not multiple of 4 bytes. So we truncate the transfer so that it
		* is suitable for such controllers, and handle the trailing bytes
		* manually after the DMA completes.
		*
		* REVISIT: It would be better if this information could be
		* retrieved directly from the DMA device in a similar way than
		* ->copy_align etc. is done.
		*/
		len = ALIGN(drv_data->len, 4);

		if (dir == DMA_TO_DEVICE) {
		dmadev = drv_data->tx_chan->device->dev;
		sgt = &drv_data->tx_sgt;
		@@ -144,12 +132,8 @@ static void pxa2xx_spi_dma_transfer_complete(struct driver_data *drv_data,
		if (!error) {
		pxa2xx_spi_unmap_dma_buffers(drv_data);

		/* Handle the last bytes of unaligned transfer */
		drv_data->tx += drv_data->tx_map_len;
		drv_data->write(drv_data);

		drv_data->rx += drv_data->rx_map_len;
		drv_data->read(drv_data);

		msg->actual_length += drv_data->len;
		msg->state = pxa2xx_spi_next_transfer(drv_data);

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