linux-kernel - Re: [RFC PATCH v4 02/11] drm/fb-helper: Set FBINFO_MISC_FIRMWARE flag for DRIVER

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Date:   Fri, 29 Apr 2022 11:14:09 +0200
From:   Thomas Zimmermann <tzimmermann@...e.de>
To:     Javier Martinez Canillas <javierm@...hat.com>,
        linux-kernel@...r.kernel.org
Cc:     David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel.vetter@...ll.ch>,
        dri-devel@...ts.freedesktop.org,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: Re: [RFC PATCH v4 02/11] drm/fb-helper: Set FBINFO_MISC_FIRMWARE flag
 for DRIVER_FIRMWARE fb

Hi

Am 29.04.22 um 10:42 schrieb Javier Martinez Canillas:
> The DRIVER_FIRMWARE flag denotes that a DRM driver uses a framebuffer
> that was initialized and provided by the system firmware for scanout.
> 
> Indicate to the fbdev subsystem that the registered framebuffer is a
> FBINFO_MISC_FIRMWARE, so that it can handle accordingly. For example,
> wold hot-unplug the associated device if asked to remove conflicting
> framebuffers.
> 
> Suggested-by: Thomas Zimmermann <tzimmermann@...e.de>
> Signed-off-by: Javier Martinez Canillas <javierm@...hat.com>
> ---
> 
> (no changes since v1)
> 
>   drivers/gpu/drm/drm_fb_helper.c | 4 ++++
>   1 file changed, 4 insertions(+)
> 
> diff --git a/drivers/gpu/drm/drm_fb_helper.c b/drivers/gpu/drm/drm_fb_helper.c
> index d265a73313c9..76dd11888621 100644
> --- a/drivers/gpu/drm/drm_fb_helper.c
> +++ b/drivers/gpu/drm/drm_fb_helper.c
> @@ -1891,6 +1891,10 @@ __drm_fb_helper_initial_config_and_unlock(struct drm_fb_helper *fb_helper,
>   		/* don't leak any physical addresses to userspace */
>   		info->flags |= FBINFO_HIDE_SMEM_START;
>   
> +	/* Indicate that the framebuffer is provided by the firmware */
> +	if (drm_core_check_feature(dev, DRIVER_FIRMWARE))
> +		info->flags |= FBINFO_MISC_FIRMWARE;
> +

Patches 1 to 3 should be squashed into one before landing.

We can do this with DRIVER_FIRMWARE. Alternatively, I'd suggest to we 
could also used the existing final parameter of 
drm_fbdev_generic_setup() to pass a flag that designates a firmware device.

>   	/* Need to drop locks to avoid recursive deadlock in
>   	 * register_framebuffer. This is ok because the only thing left to do is
>   	 * register the fbdev emulation instance in kernel_fb_helper_list. */

-- 
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Maxfeldstr. 5, 90409 Nürnberg, Germany
(HRB 36809, AG Nürnberg)
Geschäftsführer: Ivo Totev

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