Unverified Commit 8b7bd10e authored by Meghana Madhyastha's avatar Meghana Madhyastha Committed by Mark Brown
Browse files

spi/spi-bcm2835: Split transfers that exceed DLEN 



Split spi transfers into chunks of <=65532 to enable the driver to
perform DMA transfer on big buffers. The DLEN register specifies the
number of bytes to transfer in DMA mode. It is 16-bit wide and thus the
maximum DMA transfer is 65535 bytes. Set the maximum to 65532 (4 byte
aligned) since the FIFO in DMA mode is accessed in 4 byte chunks.

->max_dma_len is the value the spi core uses when splitting the buffer
into scatter gather entries.
The BCM2835 DMA block has 2 types of channels/engines:
- Normal: Max length: 1G
- Lite: Max length: 65535

Even when using a Lite channel we will not exceed the max length, so
let's drop setting ->max_dma_len.

Signed-off-by: default avatarMeghana Madhyastha <meghana.madhyastha@gmail.com>
Signed-off-by: default avatarNoralf Trønnes <noralf@tronnes.org>
Reviewed-by: default avatarLukas Wunner <lukas@wunner.de>
Signed-off-by: default avatarMark Brown <broonie@kernel.org>
parent 937e6d75

drivers/spi/spi-bcm2835.c

+11 −28
Original line number Diff line number Diff line
@@ -335,20 +335,6 @@ static int bcm2835_spi_transfer_one_irq(struct spi_master *master, 
	return 1;

}



/*

 * DMA support

 *

 * this implementation has currently a few issues in so far as it does

 * not work arrount limitations of the HW.

 *

 * the main one being that DMA transfers are limited to 16 bit

 * (so 0 to 65535 bytes) by the SPI HW due to BCM2835_SPI_DLEN

 *

 * there may be a few more border-cases we may need to address as well

 * but unfortunately this would mean splitting up the scatter-gather

 * list making it slightly unpractical...

 */



/**

 * bcm2835_spi_transfer_prologue() - transfer first few bytes without DMA

 * @master: SPI master
@@ -630,19 +616,6 @@ static bool bcm2835_spi_can_dma(struct spi_master *master, 
	if (tfr->len < BCM2835_SPI_DMA_MIN_LENGTH)

		return false;



	/* BCM2835_SPI_DLEN has defined a max transfer size as

	 * 16 bit, so max is 65535

	 * we can revisit this by using an alternative transfer

	 * method - ideally this would get done without any more

	 * interaction...

	 */

	if (tfr->len > 65535) {

		dev_warn_once(&spi->dev,

			      "transfer size of %d too big for dma-transfer\n",

			      tfr->len);

		return false;

	}



	/* return OK */

	return true;

}
@@ -707,7 +680,6 @@ static void bcm2835_dma_init(struct spi_master *master, struct device *dev) 


	/* all went well, so set can_dma */

	master->can_dma = bcm2835_spi_can_dma;

	master->max_dma_len = 65535; /* limitation by BCM2835_SPI_DLEN */

	/* need to do TX AND RX DMA, so we need dummy buffers */

	master->flags = SPI_MASTER_MUST_RX | SPI_MASTER_MUST_TX;
@@ -844,6 +816,17 @@ static int bcm2835_spi_prepare_message(struct spi_master *master, 
	struct spi_device *spi = msg->spi;

	struct bcm2835_spi *bs = spi_master_get_devdata(master);

	u32 cs = bcm2835_rd(bs, BCM2835_SPI_CS);

	int ret;



	/*

	 * DMA transfers are limited to 16 bit (0 to 65535 bytes) by the SPI HW

	 * due to DLEN. Split up transfers (32-bit FIFO aligned) if the limit is

	 * exceeded.

	 */

	ret = spi_split_transfers_maxsize(master, msg, 65532,

					  GFP_KERNEL | GFP_DMA);

	if (ret)

		return ret;



	cs &= ~(BCM2835_SPI_CS_CPOL | BCM2835_SPI_CS_CPHA);

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