[PATCH V3] dmaengine: imx-sdma: Fix SPBA bus detection on multi-SPBA platforms

[Marco Felsch]

On 26-04-20, Shengjiu Wang wrote:
> i.MX8M platforms have multiple SPBA buses under different AIPS buses.
> The current code searches the entire device tree and returns the first
> SPBA bus found, which may not be under the same AIPS bus as the SDMA
> controller.
> 
> This breaks SDMA P2P transfers because the SDMA script needs to know
> if peripherals are on SPBA or AIPS to configure watermark levels
> correctly. Using the wrong SPBA bus causes DMA timeouts and transfer
> failures.
> 
> Fix by searching for the SPBA bus under the SDMA's parent node (AIPS)
> first, then falling back to a global search for backward compatibility.
> 
> Example device tree showing the issue:
>   aips1 {
>     spba1 { sai at ...; };      /* Correct SPBA for sdma1 */
>     sdma1 at ...;
>   };
>   aips2 {
>     spba2 { uart at ...; };     /* Wrong SPBA - found first by old code */
>   };
> 
> Fixes: 8391ecf465ec ("dmaengine: imx-sdma: Add device to device support")
> Cc: stable at vger.kernel.org
> Signed-off-by: Shengjiu Wang <shengjiu.wang at nxp.com>
> ---
> changs in v3:
> - add fallback to a global search for backward compatibility, which is
>   to address comments from sashiko.dev
> - update commit subject and commit message
> - add comments in code.
> - add Cc stable tag
> - Don't add Frank's RB on v2 as there are several other changes.
> 
> changes in v2:
> - add fixes tag
> - use __free(device_node) for auto release. 
> 
>  drivers/dma/imx-sdma.c | 13 ++++++++++++-
>  1 file changed, 12 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/dma/imx-sdma.c b/drivers/dma/imx-sdma.c
> index 3d527883776b..592705af2319 100644
> --- a/drivers/dma/imx-sdma.c
> +++ b/drivers/dma/imx-sdma.c
> @@ -2364,7 +2364,18 @@ static int sdma_probe(struct platform_device *pdev)
>  			return dev_err_probe(&pdev->dev, ret,
>  					     "failed to register controller\n");
>  
> -		spba_bus = of_find_compatible_node(NULL, NULL, "fsl,spba-bus");
> +		/*
> +		 * On i.MX8M platforms with multiple SPBA buses, we need to find
> +		 * the SPBA bus that's under the same AIPS bus as this SDMA controller.
> +		 * First check the SDMA's parent (AIPS bus) for a child SPBA bus.
> +		 * If not found, fall back to searching the entire device tree for
> +		 * backward compatibility with older platforms.
> +		 */
> +		struct device_node *sdma_parent_np __free(device_node) = of_get_parent(np);
> +
> +		spba_bus = of_get_compatible_child(sdma_parent_np, "fsl,spba-bus");
> +		if (!spba_bus)
> +			spba_bus = of_find_compatible_node(NULL, NULL, "fsl,spba-bus");

And yet the search is still broken for i.MX8MP case since this platform
has two sdma engines below the bus at 30df0000.

Regards,
  Marco

>  		ret = of_address_to_resource(spba_bus, 0, &spba_res);
>  		if (!ret) {
>  			sdma->spba_start_addr = spba_res.start;
> -- 
> 2.34.1
> 
> 
> 

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