diff --git a/drivers/dma/bcm2835-dma.c b/drivers/dma/bcm2835-dma.c index b6fe198b5422f3..54e067c0d79967 100644 --- a/drivers/dma/bcm2835-dma.c +++ b/drivers/dma/bcm2835-dma.c @@ -53,11 +53,14 @@ * @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 { @@ -705,6 +708,7 @@ 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; @@ -755,6 +759,10 @@ 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 */ @@ -857,6 +865,9 @@ 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[] = { @@ -943,6 +954,14 @@ 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",