linux-kernel - Re: [PATCH v2] drm/amdgpu: register a dirty framebuffer callback for fbcon

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Message-ID: <9855fa7a-dd9d-27b8-171e-b662d417b902@amd.com>
Date:   Wed, 16 Aug 2023 16:17:34 +0200
From:   Christian König <christian.koenig@....com>
To:     Hamza Mahfooz <hamza.mahfooz@....com>,
        amd-gfx@...ts.freedesktop.org
Cc:     Srinivasan Shanmugam <srinivasan.shanmugam@....com>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        Guchun Chen <guchun.chen@....com>,
        dri-devel@...ts.freedesktop.org,
        "Pan, Xinhui" <Xinhui.Pan@....com>,
        Javier Martinez Canillas <javierm@...hat.com>,
        stable@...r.kernel.org, linux-kernel@...r.kernel.org,
        Aurabindo Pillai <aurabindo.pillai@....com>,
        Daniel Vetter <daniel@...ll.ch>,
        Alex Deucher <alexander.deucher@....com>,
        David Airlie <airlied@...il.com>,
        Christian König <christian.koenig@....com>,
        Mario Limonciello <mario.limonciello@....com>
Subject: Re: [PATCH v2] drm/amdgpu: register a dirty framebuffer callback for
 fbcon

Am 16.08.23 um 15:41 schrieb Hamza Mahfooz:
>
> On 8/16/23 01:55, Christian König wrote:
>>
>>
>> Am 15.08.23 um 19:26 schrieb Hamza Mahfooz:
>>> fbcon requires that we implement &drm_framebuffer_funcs.dirty.
>>> Otherwise, the framebuffer might take a while 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>
>>> ---
>>> v2: update variable names
>>> ---
>>>   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..d3b59f99cb7c 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(fb->comm, "[fbcon]"))
>>> +        return -ENOSYS;
>>
>> Once more to the v2 of this patch: Tests like those are a pretty big 
>> NO-GO for upstreaming.
>
> On closer inspection it is actually sufficient to check if `file` is
> NULL here (since it means that the request isn't from userspace). So, do
> you think that would be palatable for upstream?

That's certainly better than doing a string compare, but I'm not sure if 
that's sufficient.

In general drivers shouldn't have any special handling for fdcon.

You should probably have Thomas Zimmermann <tzimmermann@...e.de> take a 
look at this.

Regards,
Christian.

>
>>
>> Regards,
>> Christian.
>>
>>> +
>>> +    return drm_atomic_helper_dirtyfb(fb, file, 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;
>>