linux-kernel - Re: [PATCH] drm/rockchip: remove early framebuffers before registering the fbdev

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Message-ID: <fe3285b7-3bc3-8292-bdc2-b8e823c1772d@suse.de>
Date:   Sun, 16 May 2021 07:30:35 +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>, Sandy Huang <hjc@...k-chips.com>,
        dri-devel@...ts.freedesktop.org,
        linux-rockchip@...ts.infradead.org,
        Peter Robinson <pbrobinson@...il.com>,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH] drm/rockchip: remove early framebuffers before
 registering the fbdev

Hi

Am 16.05.21 um 00:14 schrieb Javier Martinez Canillas:
> There are drivers that register framebuffer devices very early in the boot
> process and make use of the existing framebuffer as setup by the firmware.
> 
> If one of those drivers has registered a fbdev, then the fbdev registered
> by a DRM driver won't be bound to the framebuffer console. To avoid that,
> remove any early framebuffer before registering a DRM framebuffer device.
> 
> By doing that, the fb mapped to the console is switched correctly from the
> early fbdev to the one registered by the rockchip DRM driver:
> 
>      [   40.752420] fb0: switching to rockchip-drm-fb from EFI VGA
> 
> Signed-off-by: Javier Martinez Canillas <javierm@...hat.com>
> ---
> 
>   drivers/gpu/drm/rockchip/rockchip_drm_fbdev.c | 10 ++++++++++
>   1 file changed, 10 insertions(+)
> 
> diff --git a/drivers/gpu/drm/rockchip/rockchip_drm_fbdev.c b/drivers/gpu/drm/rockchip/rockchip_drm_fbdev.c
> index 2fdc455c4ad..e3e5b63fdcc 100644
> --- a/drivers/gpu/drm/rockchip/rockchip_drm_fbdev.c
> +++ b/drivers/gpu/drm/rockchip/rockchip_drm_fbdev.c
> @@ -4,6 +4,7 @@
>    * Author:Mark Yao <mark.yao@...k-chips.com>
>    */
>   
> +#include <drm/drm_aperture.h>
>   #include <drm/drm.h>
>   #include <drm/drm_fb_helper.h>
>   #include <drm/drm_fourcc.h>
> @@ -124,6 +125,15 @@ int rockchip_drm_fbdev_init(struct drm_device *dev)
>   
>   	drm_fb_helper_prepare(dev, helper, &rockchip_drm_fb_helper_funcs);
>   
> +	/* Remove early framebuffers (e.g: simplefb or efifb) */
> +	ret = drm_aperture_remove_framebuffers(false, "rockchip-drm-fb");
> +	if (ret) {
> +		DRM_DEV_ERROR(dev->dev,
> +			      "Failed to remove early framebuffers - %d.\n",
> +			      ret);
> +		return ret;
> +	}
> +

Such code used to be part of the fbdev helpers, but it's not really 
related to fbdev functonality. Rather it controls ownership of the I/O 
ranges.

This code block should be done at the very beginning; before the driver 
tries to reserve the device's I/O ranges. Probably at [1]

Best regards
Thomas

[1] 
https://elixir.bootlin.com/linux/v5.13-rc1/source/drivers/gpu/drm/rockchip/rockchip_drm_drv.c#L116


>   	ret = drm_fb_helper_init(dev, helper);
>   	if (ret < 0) {
>   		DRM_DEV_ERROR(dev->dev,
> 

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



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