[PATCH] drm/fbdev-client: Ignore EOPNOTSUPP errors

[Thomas Zimmermann]

Hi,

sorry for the late review. I've been away for a few days.

Am 12.04.25 um 09:00 schrieb Thierry Reding:
> From: Thierry Reding <treding at nvidia.com>
>
> Recent generations of Tegra have moved the display components outside of
> host1x, leading to a device that has no CRTCs attached and hence doesn't
> support any of the modesetting functionality. When this is detected, the
> driver clears the DRIVER_MODESET and DRIVER_ATOMIC flags for the device.
>
> Unfortunately, this causes the following errors during boot:
>
>      [      15.418958] ERR KERN drm drm: [drm] *ERROR* Failed to register client: -95
>      [      15.425311] WARNING KERN drm drm: [drm] Failed to set up DRM client; error -95
>
> These originate from the fbdev client checking for the presence of the
> DRIVER_MODESET flag and returning -EOPNOTSUPP. However, if a driver does
> not support DRIVER_MODESET this is entirely expected and the error isn't
> helpful.
>
> One solution would have been to conditionally call drm_client_setup()
> only if modesetting is supported. This seems a bit redundant, however,
> and could further complicate things if ever any DRM clients are added
> that do not rely on modesetting.

These default in-kernel clients are all somewhat legacy by definition 
and the only viable use cases involve display output. There won't be any 
clients that don't output to the display. Best would be to put that 
check around drm_client_setup() in the tegra driver. [1]

if (drm->driver_features & MODESET)
   drm_client_setup()

[1] 
https://elixir.bootlin.com/linux/v6.14.5/source/drivers/gpu/drm/tegra/drm.c#L1274

If you want to get fancy, you could also add that test at the very top 
of drm_client_setup() itself; with a drm_dbg() statement noting the 
absense of modesetting.

Best regards
Thomas

>
> Instead, simply add an extra check to ignore this expected error and
> skip the fbdev client registration.
>
> Reported-by: Jonathan Hunter <jonathanh at nvidia.com>
> Signed-off-by: Thierry Reding <treding at nvidia.com>
> ---
>   drivers/gpu/drm/clients/drm_fbdev_client.c | 6 +++++-
>   1 file changed, 5 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/clients/drm_fbdev_client.c b/drivers/gpu/drm/clients/drm_fbdev_client.c
> index f894ba52bdb5..8c8552ed912e 100644
> --- a/drivers/gpu/drm/clients/drm_fbdev_client.c
> +++ b/drivers/gpu/drm/clients/drm_fbdev_client.c
> @@ -152,7 +152,11 @@ int drm_fbdev_client_setup(struct drm_device *dev, const struct drm_format_info
>   
>   	ret = drm_client_init(dev, &fb_helper->client, "fbdev", &drm_fbdev_client_funcs);
>   	if (ret) {
> -		drm_err(dev, "Failed to register client: %d\n", ret);
> +		if (ret != -EOPNOTSUPP)
> +			drm_err(dev, "Failed to register client: %d\n", ret);
> +		else
> +			ret = 0;
> +
>   		goto err_drm_client_init;
>   	}
>   

-- 
--
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Frankenstrasse 146, 90461 Nuernberg, Germany
GF: Ivo Totev, Andrew Myers, Andrew McDonald, Boudien Moerman
HRB 36809 (AG Nuernberg)