Patch "dmaengine: tegra186: Fix residual calculation" has been added to the 6.6-stable tree

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This is a note to let you know that I've just added the patch titled

    dmaengine: tegra186: Fix residual calculation

to the 6.6-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     dmaengine-tegra186-fix-residual-calculation.patch
and it can be found in the queue-6.6 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit 8c93ef3f4c744e4375eeaada0c2949ebfa702c88
Author: Akhil R <akhilrajeev@xxxxxxxxxx>
Date:   Fri Mar 15 18:14:11 2024 +0530

    dmaengine: tegra186: Fix residual calculation
    
    [ Upstream commit 30f0ced9971b2d8c8c24ae75786f9079489a012d ]
    
    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@xxxxxxxxxx>
    Reviewed-by: Jon Hunter <jonathanh@xxxxxxxxxx>
    Acked-by: Thierry Reding <treding@xxxxxxxxxx>
    Link: https://lore.kernel.org/r/20240315124411.17582-1-akhilrajeev@xxxxxxxxxx
    Signed-off-by: Vinod Koul <vkoul@xxxxxxxxxx>
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/drivers/dma/tegra186-gpc-dma.c b/drivers/dma/tegra186-gpc-dma.c
index 33b1010011009..674cf63052838 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;




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