Re: [PATCH 1/2] serial: use dmaengine_get_dma_device() instead of chan->device->dev

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [High] dma-mapping: asymmetric dma_map_single/unmap pair in pl011
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commit fb77536d75ed603638aebc851f73960ddf8efe10
Author: Frank Li <Frank.Li@nxp.com>

serial: use dmaengine_get_dma_device() instead of chan->device->dev

This commit replaces direct access to chan->device->dev with the
dmaengine_get_dma_device() API across multiple serial drivers. This correctly
handles per-channel IOMMU mappings and prepares for making DMA engine
provider structures private.

Link: https://lore.kernel.org/imx/67966b47-22cb-4b07-80c7-2044f557dbcb@app.fastmail.com/

> diff --git a/drivers/tty/serial/amba-pl011.c b/drivers/tty/serial/amba-pl011.c
> index c4824c201e1c3..86729ddbdadc8 100644
> --- a/drivers/tty/serial/amba-pl011.c
> +++ b/drivers/tty/serial/amba-pl011.c

[ ... ]

> @@ -609,7 +609,7 @@ static void pl011_dma_tx_callback(void *data)
>  
>  	uart_port_lock_irqsave(&uap->port, &flags);
>  	if (uap->dmatx.queued)
> -		dma_unmap_single(dmatx->chan->device->dev, dmatx->dma,
> +		dma_unmap_single(dmaengine_get_dma_device(dmatx->chan), dmatx->dma,

[Severity: High]
Does this change create an asymmetric map/unmap pair in the PL011 driver?

By updating pl011_dma_tx_callback() to use dmaengine_get_dma_device() for the
unmap operation, it appears to no longer match the map operation in
pl011_dma_tx_refill() which was not updated in this patch:

drivers/tty/serial/amba-pl011.c:pl011_dma_tx_refill() {
    ...
	dmatx->dma = dma_map_single(dma_dev->dev, dmatx->buf, count,
				    DMA_TO_DEVICE);
    ...
}

The DMA API requires the exact same device pointer to be used for both
mapping and unmapping. On platforms where the DMA engine provides per-channel
devices, dmaengine_get_dma_device() will return a different device pointer
than the raw device pointer used during mapping.

Could this break DMA tracking or cause IOMMU faults during standard TX
operations? Should the map operation in pl011_dma_tx_refill() be updated to
use the new API as well?

>  				 dmatx->len, DMA_TO_DEVICE);
>  
>  	dmacr = uap->dmacr;

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Sashiko AI review · https://sashiko.dev/#/patchset/20260925200850.1678179-1-Frank.Li@oss.nxp.com?part=1