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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: Meghana Madhyastha <meghana.madhyastha@gmail.com>
Signed-off-by: Noralf Trønnes <noralf@tronnes.org>
Reviewed-by: Lukas Wunner <lukas@wunner.de>
Signed-off-by: Mark Brown <broonie@kernel.org>
This commit is contained in:
Meghana Madhyastha 2019-04-13 20:24:14 +02:00 committed by Mark Brown
parent 937e6d7564
commit 8b7bd10eb0
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GPG Key ID: 24D68B725D5487D0
1 changed files with 11 additions and 28 deletions
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39
drivers/spi/spi-bcm2835.c
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@ -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);