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-rw-r--r--drivers/dma/bcm2835-dma.c19
1 files changed, 19 insertions, 0 deletions
diff --git a/drivers/dma/bcm2835-dma.c b/drivers/dma/bcm2835-dma.c
index 14358faf3bff..67100e4e1083 100644
--- a/drivers/dma/bcm2835-dma.c
+++ b/drivers/dma/bcm2835-dma.c
@@ -42,11 +42,14 @@
* @ddev: DMA device
* @base: base address of register map
* @dma_parms: DMA parameters (to convey 1 GByte max segment size to clients)
+ * @zero_page: bus address of zero page (to detect transactions copying from
+ * zero page and avoid accessing memory if so)
*/
struct bcm2835_dmadev {
struct dma_device ddev;
void __iomem *base;
struct device_dma_parameters dma_parms;
+ dma_addr_t zero_page;
};
struct bcm2835_dma_cb {
@@ -693,6 +696,7 @@ static struct dma_async_tx_descriptor *bcm2835_dma_prep_dma_cyclic(
size_t period_len, enum dma_transfer_direction direction,
unsigned long flags)
{
+ struct bcm2835_dmadev *od = to_bcm2835_dma_dev(chan->device);
struct bcm2835_chan *c = to_bcm2835_dma_chan(chan);
struct bcm2835_desc *d;
dma_addr_t src, dst;
@@ -743,6 +747,10 @@ static struct dma_async_tx_descriptor *bcm2835_dma_prep_dma_cyclic(
dst = c->cfg.dst_addr;
src = buf_addr;
info |= BCM2835_DMA_D_DREQ | BCM2835_DMA_S_INC;
+
+ /* non-lite channels can write zeroes w/o accessing memory */
+ if (buf_addr == od->zero_page && !c->is_lite_channel)
+ info |= BCM2835_DMA_S_IGNORE;
}
/* calculate number of frames */
@@ -845,6 +853,9 @@ static void bcm2835_dma_free(struct bcm2835_dmadev *od)
list_del(&c->vc.chan.device_node);
tasklet_kill(&c->vc.task);
}
+
+ dma_unmap_page_attrs(od->ddev.dev, od->zero_page, PAGE_SIZE,
+ DMA_TO_DEVICE, DMA_ATTR_SKIP_CPU_SYNC);
}
static const struct of_device_id bcm2835_dma_of_match[] = {
@@ -927,6 +938,14 @@ static int bcm2835_dma_probe(struct platform_device *pdev)
platform_set_drvdata(pdev, od);
+ od->zero_page = dma_map_page_attrs(od->ddev.dev, ZERO_PAGE(0), 0,
+ PAGE_SIZE, DMA_TO_DEVICE,
+ DMA_ATTR_SKIP_CPU_SYNC);
+ if (dma_mapping_error(od->ddev.dev, od->zero_page)) {
+ dev_err(&pdev->dev, "Failed to map zero page\n");
+ return -ENOMEM;
+ }
+
/* Request DMA channel mask from device tree */
if (of_property_read_u32(pdev->dev.of_node,
"brcm,dma-channel-mask",