dma: tegra: avoid overflow of byte tracking
PATCH 1/6 dma: tegra: avoid overflow of byte tracking
Quoted 32 lines · Ben Dooks
The
dma_desc->bytes_transferredcounter tracks the number of bytes moved by the DMA channel. This is then used to calculate the information passed back in the in thetegra_dma_tx_statuscallback, which is usually fine.When the DMA channel is configured as continous, then the
bytes_transferredcounter 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_transferredfield 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.
Signed-off-by Ben Dooks <[email protected]>--- drivers/dma/tegra20-apb-dma.c | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-)drivers/dma/tegra20-apb-dma.c +0
-0@@ -636,7 +636,10 @@ static void handle_cont_sngl_cycle_dma_done(struct tegra_dma_channel *tdc,
drivers/dma/tegra20-apb-dma.c static void handle_cont_sngl_cycle_dma_done(struct tegra_dma_channel *tdc, · line 645
Quoted 10 lines
drivers/dma/tegra20-apb-dma.c +4
-1sgreq =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)