Re: [PATCH] dmaengine: mediatek: uart: synchronize completion callbacks

[Frank Li <Frank.li@oss.nxp.com>]

On Wed, Oct 21, 2026 at 03:13:24PM -0600, James Hilliard wrote:
> Terminating a UART APDMA channel waits for its interrupt handler, but
> completion callbacks run in the virt-dma tasklet. A callback already
> removed from desc_completed can still be running after termination
> returns. With no device_synchronize hook, dmaengine_synchronize() does
> not wait for that callback either.
>
> Implement the hook using vchan_synchronize(). This lets clients finish
> asynchronous cancellation before reusing callback state or freeing DMA
> buffers. Keep the callback wait out of device_terminate_all so it can be
> performed without locks acquired by the callback.
>
> Fixes: 9135408c3ace ("dmaengine: mediatek: Add MediaTek UART APDMA support")
> Signed-off-by: James Hilliard <james.hilliard1@gmail.com>
> ---
>  drivers/dma/mediatek/mtk-uart-apdma.c | 8 ++++++++
>  1 file changed, 8 insertions(+)
>
> diff --git a/drivers/dma/mediatek/mtk-uart-apdma.c b/drivers/dma/mediatek/mtk-uart-apdma.c
> index f74e9a328588..7583c287da5d 100644
> --- a/drivers/dma/mediatek/mtk-uart-apdma.c
> +++ b/drivers/dma/mediatek/mtk-uart-apdma.c
> @@ -440,6 +440,13 @@ static int mtk_uart_apdma_terminate_all(struct dma_chan *chan)
>  	return 0;
>  }
>
> +static void mtk_uart_apdma_synchronize(struct dma_chan *chan)
> +{
> +	struct mtk_chan *c = to_mtk_uart_apdma_chan(chan);
> +
> +	vchan_synchronize(&c->vc);

Can you create vchan API, which use dma_chan as agurement like, basic
move this function into vchan-dma.h

vchan_dma_synchronize(struct dma_chan *chan)

So below callback direct use this API and avoid other drivers duplicate
this segment code.

Frank

> +}
> +
>  static int mtk_uart_apdma_device_pause(struct dma_chan *chan)
>  {
>  	struct mtk_chan *c = to_mtk_uart_apdma_chan(chan);
> @@ -514,6 +521,7 @@ static int mtk_uart_apdma_probe(struct platform_device *pdev)
>  	mtkd->ddev.device_config = mtk_uart_apdma_slave_config;
>  	mtkd->ddev.device_pause = mtk_uart_apdma_device_pause;
>  	mtkd->ddev.device_terminate_all = mtk_uart_apdma_terminate_all;
> +	mtkd->ddev.device_synchronize = mtk_uart_apdma_synchronize;
>  	mtkd->ddev.src_addr_widths = BIT(DMA_SLAVE_BUSWIDTH_1_BYTE);
>  	mtkd->ddev.dst_addr_widths = BIT(DMA_SLAVE_BUSWIDTH_1_BYTE);
>  	mtkd->ddev.directions = BIT(DMA_DEV_TO_MEM) | BIT(DMA_MEM_TO_DEV);
>
> ---
> base-commit: 93f51579e7df248780214094418f205253383cc5
> change-id: 20261021-submit-mtk-uart-dma-synchronize-v1-158c8303b574
>
> Best regards,
> --
> James Hilliard <james.hilliard1@gmail.com>
>