diff mbox series

[v2,RESEND] dmaengine: tegra186: Fix residual calculation

Message ID 20240315124411.17582-1-akhilrajeev@nvidia.com (mailing list archive)
State Accepted
Commit 30f0ced9971b2d8c8c24ae75786f9079489a012d
Headers show
Series [v2,RESEND] dmaengine: tegra186: Fix residual calculation | expand

Commit Message

Akhil R March 15, 2024, 12:44 p.m. UTC
The existing residual calculation returns an incorrect value when
bytes_xfer == bytes_req. This scenario occurs particularly with drivers
like UART where DMA is scheduled for maximum number of bytes and is
terminated when the bytes inflow stops. At higher baud rates, it could
request the tx_status while there is no bytes left to transfer. This will
lead to incorrect residual being set. Hence return residual as '0' when
bytes transferred equals to the bytes requested.

Fixes: ee17028009d4 ("dmaengine: tegra: Add tegra gpcdma driver")
Signed-off-by: Akhil R <akhilrajeev@nvidia.com>
Reviewed-by: Jon Hunter <jonathanh@nvidia.com>
---
v1->v2:
* corrected typo - s/exisiting/existing/

 drivers/dma/tegra186-gpc-dma.c | 3 +++
 1 file changed, 3 insertions(+)

Comments

Thierry Reding March 25, 2024, 1:30 p.m. UTC | #1
On Fri Mar 15, 2024 at 1:44 PM CET, Akhil R wrote:
> The existing residual calculation returns an incorrect value when
> bytes_xfer == bytes_req. This scenario occurs particularly with drivers
> like UART where DMA is scheduled for maximum number of bytes and is
> terminated when the bytes inflow stops. At higher baud rates, it could
> request the tx_status while there is no bytes left to transfer. This will
> lead to incorrect residual being set. Hence return residual as '0' when
> bytes transferred equals to the bytes requested.
>
> Fixes: ee17028009d4 ("dmaengine: tegra: Add tegra gpcdma driver")
> Signed-off-by: Akhil R <akhilrajeev@nvidia.com>
> Reviewed-by: Jon Hunter <jonathanh@nvidia.com>
> ---
> v1->v2:
> * corrected typo - s/exisiting/existing/
>
>  drivers/dma/tegra186-gpc-dma.c | 3 +++
>  1 file changed, 3 insertions(+)

Acked-by: Thierry Reding <treding@nvidia.com>
Vinod Koul March 28, 2024, 7:39 a.m. UTC | #2
On Fri, 15 Mar 2024 18:14:11 +0530, Akhil R wrote:
> The existing residual calculation returns an incorrect value when
> bytes_xfer == bytes_req. This scenario occurs particularly with drivers
> like UART where DMA is scheduled for maximum number of bytes and is
> terminated when the bytes inflow stops. At higher baud rates, it could
> request the tx_status while there is no bytes left to transfer. This will
> lead to incorrect residual being set. Hence return residual as '0' when
> bytes transferred equals to the bytes requested.
> 
> [...]

Applied, thanks!

[1/1] dmaengine: tegra186: Fix residual calculation
      commit: 30f0ced9971b2d8c8c24ae75786f9079489a012d

Best regards,
diff mbox series

Patch

diff --git a/drivers/dma/tegra186-gpc-dma.c b/drivers/dma/tegra186-gpc-dma.c
index 88547a23825b..3642508e88bb 100644
--- a/drivers/dma/tegra186-gpc-dma.c
+++ b/drivers/dma/tegra186-gpc-dma.c
@@ -746,6 +746,9 @@  static int tegra_dma_get_residual(struct tegra_dma_channel *tdc)
 	bytes_xfer = dma_desc->bytes_xfer +
 		     sg_req[dma_desc->sg_idx].len - (wcount * 4);
 
+	if (dma_desc->bytes_req == bytes_xfer)
+		return 0;
+
 	residual = dma_desc->bytes_req - (bytes_xfer % dma_desc->bytes_req);
 
 	return residual;