From: Meghana Madhyastha <meghana.madhyas...@gmail.com>
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.madhyas...@gmail.com>
Signed-off-by: Noralf Trønnes <nor...@tronnes.org>
---
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);
--
2.20.1
_______________________________________________
dri-devel mailing list
dri-devel@lists.freedesktop.org
https://lists.freedesktop.org/mailman/listinfo/dri-devel
