linux-kernel - Re: [PATCH V2] dmaengine: Add NULL check in lpc18xx_dmamux

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Message-ID: <3ed9f3bc-60f5-4c40-97b5-53d6af4d78c9@mleia.com>
Date: Mon, 16 Jun 2025 18:23:58 +0300
From: Vladimir Zapolskiy <vz@...ia.com>
To: Charles Han <hanchunchao@...pur.com>, eugen.hristev@...aro.org,
 vkoul@...nel.org, manabian@...il.com
Cc: dmaengine@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH V2] dmaengine: Add NULL check in lpc18xx_dmamux_reserve()

On 6/16/25 13:44, Charles Han wrote:
> The function of_find_device_by_node() may return NULL if the device
> node is not found or CONFIG_OF not defined.

DMA_OF depends on OF, and the driver depends on OF as it's stated
in the drivers/dma/Kconfig, so this is not an issue.

Next, is it possible here to get of_find_device_by_node() returning
NULL? I don't think so, and then it's unclear which problem is supposed
to be fixed by this change, and therefore the change should be dropped.

> Add  check whether the return value is NULL and set the error code
> to be returned as -ENODEV.
> 
> Fixes: e5f4ae84be74 ("dmaengine: add driver for lpc18xx dmamux")
> Signed-off-by: Charles Han <hanchunchao@...pur.com>
> ---
>   drivers/dma/lpc18xx-dmamux.c | 10 ++++++++--
>   1 file changed, 8 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/dma/lpc18xx-dmamux.c b/drivers/dma/lpc18xx-dmamux.c
> index 2b6436f4b193..f61183a1d0ba 100644
> --- a/drivers/dma/lpc18xx-dmamux.c
> +++ b/drivers/dma/lpc18xx-dmamux.c
> @@ -53,11 +53,17 @@ static void lpc18xx_dmamux_free(struct device *dev, void *route_data)
>   static void *lpc18xx_dmamux_reserve(struct of_phandle_args *dma_spec,
>   				    struct of_dma *ofdma)
>   {
> -	struct platform_device *pdev = of_find_device_by_node(ofdma->of_node);
> -	struct lpc18xx_dmamux_data *dmamux = platform_get_drvdata(pdev);
> +	struct platform_device *pdev;
> +	struct lpc18xx_dmamux_data *dmamux;

The list of declared/initialized local variables is deliberately sorted
in so called reverse Christmas tree order, please keep the sorting order.

>   	unsigned long flags;
>   	unsigned mux;
>   
> +	pdev = of_find_device_by_node(ofdma->of_node);
> +	if (!pdev)
> +		return ERR_PTR(-ENODEV);
> +
> +	dmamux = platform_get_drvdata(pdev);
> +
>   	if (dma_spec->args_count != 3) {
>   		dev_err(&pdev->dev, "invalid number of dma mux args\n");
>   		return ERR_PTR(-EINVAL);

--
Best wishes,
Vladimir