linux-kernel - Re: [PATCH v2] media: platform: Use dev_err_probe instead of dev

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Date:   Wed, 26 Jul 2023 17:28:35 +0300
From:   Laurent Pinchart <laurent.pinchart@...asonboard.com>
To:     Wang Ming <machel@...o.com>
Cc:     Mauro Carvalho Chehab <mchehab@...nel.org>,
        Michal Simek <michal.simek@....com>,
        linux-media@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org, opensource.kernel@...o.com
Subject: Re: [PATCH v2] media: platform: Use dev_err_probe instead of dev_err

Hi Wang,

Thank you for the patch.

On Wed, Jul 26, 2023 at 07:51:58PM +0800, Wang Ming wrote:
> It is possible that dma_request_chan will return EPROBE_DEFER,
> which means that dma->xdev->dev is not ready yet. In this case,
> dev_err(dma->xdev->dev), there will be no output. This patch
> fixes the bug.

It's not a bug. The existing code works as expected. dev_err_probe() is
nicer though, as it records the reason for the probe deferral. Here's a
proposal for a better commit message:

  It is possible that dma_request_chan() returns EPROBE_DEFER, in which
  case the driver defers probing without printing any message. Use
  dev_err_probe() to record the probe deferral cause and ease debugging.

If you're fine with this, there's no need to resubmit, I'll update the
commit message locally and merge the patch.

Reviewed-by: Laurent Pinchart <laurent.pinchart@...asonboard.com>

> Signed-off-by: Wang Ming <machel@...o.com>
> ---
>  drivers/media/platform/xilinx/xilinx-dma.c | 5 ++---
>  1 file changed, 2 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/media/platform/xilinx/xilinx-dma.c b/drivers/media/platform/xilinx/xilinx-dma.c
> index 80d6f5b072ea..16ad39bef6c6 100644
> --- a/drivers/media/platform/xilinx/xilinx-dma.c
> +++ b/drivers/media/platform/xilinx/xilinx-dma.c
> @@ -708,9 +708,8 @@ int xvip_dma_init(struct xvip_composite_device *xdev, struct xvip_dma *dma,
>  	snprintf(name, sizeof(name), "port%u", port);
>  	dma->dma = dma_request_chan(dma->xdev->dev, name);
>  	if (IS_ERR(dma->dma)) {
> -		ret = PTR_ERR(dma->dma);
> -		if (ret != -EPROBE_DEFER)
> -			dev_err(dma->xdev->dev, "no VDMA channel found\n");
> +		ret = dev_err_probe(dma->xdev->dev, PTR_ERR(dma->dma),
> +			"no VDMA channel found\n");
>  		goto error;
>  	}
>  

-- 
Regards,

Laurent Pinchart