From: Ben Dooks ben.dooks@codethink.co.uk
[ Upstream commit e486df39305864604b7e25f2a95d51039517ac57 ]
The dma_desc->bytes_transferred counter tracks the number of bytes moved by the DMA channel. This is then used to calculate the information passed back in the in the tegra_dma_tx_status callback, which is usually fine.
When the DMA channel is configured as continous, then the bytes_transferred counter will increase over time and eventually overflow to become negative so the residue count will become invalid and the ALSA sound-dma code will report invalid hardware pointer values to the application. This results in some users becoming confused about the playout position and putting audio data in the wrong place.
To fix this issue, always ensure the bytes_transferred field is modulo the size of the request. We only do this for the case of the cyclic transfer done ISR as anyone attempting to move 2GiB of DMA data in one transfer is unlikely.
Note, we don't fix the issue that we should /never/ transfer a negative number of bytes so we could make those fields unsigned.
Reviewed-by: Dmitry Osipenko digetx@gmail.com Signed-off-by: Ben Dooks ben.dooks@codethink.co.uk Acked-by: Jon Hunter jonathanh@nvidia.com Signed-off-by: Vinod Koul vkoul@kernel.org Signed-off-by: Sasha Levin sashal@kernel.org --- drivers/dma/tegra20-apb-dma.c | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-)
diff --git a/drivers/dma/tegra20-apb-dma.c b/drivers/dma/tegra20-apb-dma.c index 3722b9d8d9fe..22f7f0c68a48 100644 --- a/drivers/dma/tegra20-apb-dma.c +++ b/drivers/dma/tegra20-apb-dma.c @@ -635,7 +635,10 @@ static void handle_cont_sngl_cycle_dma_done(struct tegra_dma_channel *tdc,
sgreq = list_first_entry(&tdc->pending_sg_req, typeof(*sgreq), node); dma_desc = sgreq->dma_desc; - dma_desc->bytes_transferred += sgreq->req_len; + /* if we dma for long enough the transfer count will wrap */ + dma_desc->bytes_transferred = + (dma_desc->bytes_transferred + sgreq->req_len) % + dma_desc->bytes_requested;
/* Callback need to be call */ if (!dma_desc->cb_count)