linux-kernel - Re: [PATCH 11/60] drm/gud: Add support for the nomodeset kernel parameter

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Date:   Wed, 15 Dec 2021 22:37:39 +0100
From:   Noralf Trønnes <noralf@...nnes.org>
To:     Javier Martinez Canillas <javierm@...hat.com>,
        linux-kernel@...r.kernel.org, dri-devel@...ts.freedesktop.org
Subject: Re: [PATCH 11/60] drm/gud: Add support for the nomodeset kernel
 parameter



Den 15.12.2021 01.59, skrev Javier Martinez Canillas:
> According to disable Documentation/admin-guide/kernel-parameters.txt, this
> parameter can be used to disable kernel modesetting.
> 
> DRM drivers will not perform display-mode changes or accelerated rendering
> and only the systewm system framebuffer will be available if it was set-up.
> 
> But only a few DRM drivers currently check for nomodeset, make this driver
> to also support the command line parameter.
> 
> Signed-off-by: Javier Martinez Canillas <javierm@...hat.com>
> ---
> 

I don't understand why this is applicable to USB drivers, there's no way
the firmware can setup a framebuffer and continue pushing pixels over
USB when Linux has been given control over the USB bus?

The same argument goes for the SPI drivers in drm/tiny/ as well.

Noralf.

>  drivers/gpu/drm/gud/gud_drv.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/drivers/gpu/drm/gud/gud_drv.c b/drivers/gpu/drm/gud/gud_drv.c
> index 3f9d4b9a1e3d..4d253d249512 100644
> --- a/drivers/gpu/drm/gud/gud_drv.c
> +++ b/drivers/gpu/drm/gud/gud_drv.c
> @@ -446,6 +446,9 @@ static int gud_probe(struct usb_interface *intf, const struct usb_device_id *id)
>  	u32 *formats;
>  	int ret, i;
>  
> +	if (drm_firmware_drivers_only())
> +		return -ENODEV;
> +
>  	ret = usb_find_bulk_out_endpoint(intf->cur_altsetting, &bulk_out);
>  	if (ret)
>  		return ret;
>