From 8b7bd10eb00d02e74a75556ba1d85b5e2d568caf Mon Sep 17 00:00:00 2001 From: Meghana Madhyastha Date: Sat, 13 Apr 2019 20:24:14 +0200 Subject: [PATCH] spi/spi-bcm2835: Split transfers that exceed DLEN MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit 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 Signed-off-by: Noralf Trønnes Reviewed-by: Lukas Wunner Signed-off-by: Mark Brown --- drivers/spi/spi-bcm2835.c | 39 +++++++++++---------------------------- 1 file changed, 11 insertions(+), 28 deletions(-) diff --git a/drivers/spi/spi-bcm2835.c b/drivers/spi/spi-bcm2835.c index 35aebdfd3b4e..8aa22713c483 100644 --- a/drivers/spi/spi-bcm2835.c +++ b/drivers/spi/spi-bcm2835.c @@ -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);