linux-kernel - Re: [PATCH 2/2] drm/rockchip: dsi: Don't log errors on deferred dphy

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Message-ID: <yrm6r4urzf5hvnui53cvepw2loqvuhydalq6haw7qmpktor5y5@zjc34wlcoeg2>
Date: Fri, 8 Nov 2024 15:08:38 +0100
From: Sebastian Reichel <sebastian.reichel@...labora.com>
To: Dragan Simic <dsimic@...jaro.org>
Cc: linux-rockchip@...ts.infradead.org, dri-devel@...ts.freedesktop.org, 
	heiko@...ech.de, hjc@...k-chips.com, andy.yan@...k-chips.com, 
	maarten.lankhorst@...ux.intel.com, mripard@...nel.org, tzimmermann@...e.de, airlied@...il.com, 
	simona@...ll.ch, linux-arm-kernel@...ts.infradead.org, 
	linux-kernel@...r.kernel.org, Diederik de Haas <didi.debian@...ow.org>
Subject: Re: [PATCH 2/2] drm/rockchip: dsi: Don't log errors on deferred dphy

Hi,

On Fri, Nov 08, 2024 at 02:53:58PM +0100, Dragan Simic wrote:
> Deferred driver probing shouldn't result in errors or warnings being logged,
> because their presence in the kernel log provides no value and may actually
> cause false impression that some issues exist.  Thus, let's no longer produce
> error messages when getting the dphy results in deferred probing.
> 
> This prevents misleading error messages like the following one, which was
> observed on a Pine64 PineTab2, from appearing in the kernel log.  To make
> matters worse, the following error message was observed appearing multiple
> times in the kernel log of a single PineTab2 boot:
> 
>   dw-mipi-dsi-rockchip fe060000.dsi: [drm:dw_mipi_dsi_rockchip_probe \
>   [rockchipdrm]] *ERROR* failed to get mipi dphy: -517
> 
> At the same time, make the adjusted logged message a bit more consistent with
> the other logged messages by capitalizing its first word.
> 
> Reported-by: Diederik de Haas <didi.debian@...ow.org>
> Signed-off-by: Dragan Simic <dsimic@...jaro.org>
> ---

From include/drm/drm_print.h:

 * DRM_DEV_ERROR() - Error output.
 *
 * NOTE: this is deprecated in favor of drm_err() or dev_err().

The recommended way to do this nowadays looks like this:

return dev_err_probe(dev, PTR_ERR(dsi->phy), "Failed to get mipi dphy");

That will not print anything for -EPROBE_DEFER, but capture
the reason and make it available through
/sys/kernel/debug/devices_deferred if the device never probes.

Greetings,

-- Sebastian

>  drivers/gpu/drm/rockchip/dw-mipi-dsi-rockchip.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/rockchip/dw-mipi-dsi-rockchip.c b/drivers/gpu/drm/rockchip/dw-mipi-dsi-rockchip.c
> index f451e70efbdd..ffa7f2bc640d 100644
> --- a/drivers/gpu/drm/rockchip/dw-mipi-dsi-rockchip.c
> +++ b/drivers/gpu/drm/rockchip/dw-mipi-dsi-rockchip.c
> @@ -1387,7 +1387,8 @@ static int dw_mipi_dsi_rockchip_probe(struct platform_device *pdev)
>  	dsi->phy = devm_phy_optional_get(dev, "dphy");
>  	if (IS_ERR(dsi->phy)) {
>  		ret = PTR_ERR(dsi->phy);
> -		DRM_DEV_ERROR(dev, "failed to get mipi dphy: %d\n", ret);
> +		if (ret != -EPROBE_DEFER)
> +			DRM_DEV_ERROR(dev, "Failed to get mipi dphy: %d\n", ret);
>  		return ret;
>  	}
>  

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