linux-kernel - Re: [PATCH] drm/amdgpu: register a dirty framebuffer callback for fbcon

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Date:   Wed, 16 Aug 2023 07:48:04 +0200
From:   Christian König <christian.koenig@....com>
To:     Hamza Mahfooz <hamza.mahfooz@....com>,
        amd-gfx@...ts.freedesktop.org
Cc:     Aurabindo Pillai <aurabindo.pillai@....com>,
        Mario Limonciello <mario.limonciello@....com>,
        stable@...r.kernel.org, Alex Deucher <alexander.deucher@....com>,
        "Pan, Xinhui" <Xinhui.Pan@....com>,
        David Airlie <airlied@...il.com>,
        Daniel Vetter <daniel@...ll.ch>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        Javier Martinez Canillas <javierm@...hat.com>,
        Srinivasan Shanmugam <srinivasan.shanmugam@....com>,
        Guchun Chen <guchun.chen@....com>,
        dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] drm/amdgpu: register a dirty framebuffer callback for
 fbcon

Am 15.08.23 um 19:10 schrieb Hamza Mahfooz:
> fbcon requires that we implement &drm_framebuffer_funcs.dirty.
> Otherwise, the framebuffer might take awhile to flush (which would
> manifest as noticeable lag). However, we can't enable this callback for
> non-fbcon cases since it might cause too many atomic commits to be made
> at once. So, implement amdgpu_dirtyfb() and only enable it for fbcon
> framebuffers on devices that support atomic KMS.
>
> Cc: Aurabindo Pillai <aurabindo.pillai@....com>
> Cc: Mario Limonciello <mario.limonciello@....com>
> Cc: stable@...r.kernel.org # 6.1+
> Link: https://gitlab.freedesktop.org/drm/amd/-/issues/2519
> Signed-off-by: Hamza Mahfooz <hamza.mahfooz@....com>
> ---
>   drivers/gpu/drm/amd/amdgpu/amdgpu_display.c | 26 ++++++++++++++++++++-
>   1 file changed, 25 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_display.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_display.c
> index d20dd3f852fc..743db9aee68c 100644
> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_display.c
> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_display.c
> @@ -38,6 +38,8 @@
>   #include <linux/pci.h>
>   #include <linux/pm_runtime.h>
>   #include <drm/drm_crtc_helper.h>
> +#include <drm/drm_damage_helper.h>
> +#include <drm/drm_drv.h>
>   #include <drm/drm_edid.h>
>   #include <drm/drm_fb_helper.h>
>   #include <drm/drm_gem_framebuffer_helper.h>
> @@ -532,11 +534,29 @@ bool amdgpu_display_ddc_probe(struct amdgpu_connector *amdgpu_connector,
>   	return true;
>   }
>   
> +static int amdgpu_dirtyfb(struct drm_framebuffer *fb, struct drm_file *file,
> +			  unsigned int flags, unsigned int color,
> +			  struct drm_clip_rect *clips, unsigned int num_clips)
> +{
> +
> +	if (strcmp(framebuffer->comm, "[fbcon]"))
> +		return -ENOSYS;

Checks like this are a pretty big NO-GO.

I'm not an expert for the display stuff, but in general this here looks 
like a pretty ugly hack.

Regards,
Christian.

> +
> +	return drm_atomic_helper_dirtyfb(framebuffer, file_priv, flags, color,
> +					 clips, num_clips);
> +}
> +
>   static const struct drm_framebuffer_funcs amdgpu_fb_funcs = {
>   	.destroy = drm_gem_fb_destroy,
>   	.create_handle = drm_gem_fb_create_handle,
>   };
>   
> +static const struct drm_framebuffer_funcs amdgpu_fb_funcs_atomic = {
> +	.destroy = drm_gem_fb_destroy,
> +	.create_handle = drm_gem_fb_create_handle,
> +	.dirty = amdgpu_dirtyfb
> +};
> +
>   uint32_t amdgpu_display_supported_domains(struct amdgpu_device *adev,
>   					  uint64_t bo_flags)
>   {
> @@ -1139,7 +1159,11 @@ static int amdgpu_display_gem_fb_verify_and_init(struct drm_device *dev,
>   	if (ret)
>   		goto err;
>   
> -	ret = drm_framebuffer_init(dev, &rfb->base, &amdgpu_fb_funcs);
> +	if (drm_drv_uses_atomic_modeset(dev))
> +		ret = drm_framebuffer_init(dev, &rfb->base,
> +					   &amdgpu_fb_funcs_atomic);
> +	else
> +		ret = drm_framebuffer_init(dev, &rfb->base, &amdgpu_fb_funcs);
>   
>   	if (ret)
>   		goto err;