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

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Message-ID: <fb1dcbcf-0467-4a68-9d17-2a75dfcdc1d1@linaro.org>
Date: Mon, 16 Jun 2025 14:24:15 +0300
From: Eugen Hristev <eugen.hristev@...aro.org>
To: Charles Han <hanchunchao@...pur.com>, vkoul@...nel.org, vz@...ia.com,
 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.
> 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>

Can you have the subject include the driver which you are modifying ? if
you say `dmaengine: Add...` it looks like you are modifying the core.
> ---
>  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;
>  	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);


As I see it, the function lpc18xx_dmamux_reserve is only used as passed
to of_dma_router_register . In every driver, functions that have a
similar role are written in the same way, not checking if
of_find_device_by_node fails.
Can you detail what happens in your case that of_find_device_by_node
would fail ?
Would it be required to have this check in all the other drivers ?

Eugen