linux-kernel - Re: [PATCH v3 3/3] drm/amdgpu: Implement check_async

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Message-ID: <ZbjVyI_AnTBHACT8@phenom.ffwll.local>
Date: Tue, 30 Jan 2024 11:56:08 +0100
From: Daniel Vetter <daniel@...ll.ch>
To: André Almeida <andrealmeid@...lia.com>
Cc: dri-devel@...ts.freedesktop.org, amd-gfx@...ts.freedesktop.org,
	linux-kernel@...r.kernel.org, kernel-dev@...lia.com,
	alexander.deucher@....com, christian.koenig@....com,
	Simon Ser <contact@...rsion.fr>,
	Pekka Paalanen <ppaalanen@...il.com>, daniel@...ll.ch,
	Daniel Stone <daniel@...ishbar.org>,
	'Marek Olšák' <maraeo@...il.com>,
	Dave Airlie <airlied@...il.com>, ville.syrjala@...ux.intel.com,
	Xaver Hugl <xaver.hugl@...il.com>, Joshua Ashton <joshua@...ggi.es>,
	Michel Dänzer <michel.daenzer@...lbox.org>
Subject: Re: [PATCH v3 3/3] drm/amdgpu: Implement check_async_props for planes

On Sun, Jan 28, 2024 at 06:25:15PM -0300, André Almeida wrote:
> AMD GPUs can do async flips with changes on more properties than just
> the FB ID, so implement a custom check_async_props for AMD planes.
> 
> Allow amdgpu to do async flips with overlay planes as well.
> 
> Signed-off-by: André Almeida <andrealmeid@...lia.com>
> ---
> v3: allow overlay planes

This comment very much written with a lack of clearly better ideas, but:

Do we really need this much flexibility, especially for the first driver
adding the first few additional properties?

A simple bool on struct drm_plane to indicate whether async flips are ok
or not should also do this job here? Maybe a bit of work to roll that out
to the primary planes for current drivers, but not much. And wouldn't need
drivers to implement some very uapi-marshalling atomic code ...

Also we could probably remove the current drm_mode_config.async_flip flag
and entirely replace it with the per-plane one.
-Sima
> 
>  .../amd/display/amdgpu_dm/amdgpu_dm_plane.c   | 29 +++++++++++++++++++
>  1 file changed, 29 insertions(+)
> 
> diff --git a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_plane.c b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_plane.c
> index 116121e647ca..ed75b69636b4 100644
> --- a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_plane.c
> +++ b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_plane.c
> @@ -25,6 +25,7 @@
>   */
>  
>  #include <drm/drm_atomic_helper.h>
> +#include <drm/drm_atomic_uapi.h>
>  #include <drm/drm_blend.h>
>  #include <drm/drm_gem_atomic_helper.h>
>  #include <drm/drm_plane_helper.h>
> @@ -1430,6 +1431,33 @@ static void amdgpu_dm_plane_drm_plane_destroy_state(struct drm_plane *plane,
>  	drm_atomic_helper_plane_destroy_state(plane, state);
>  }
>  
> +static int amdgpu_dm_plane_check_async_props(struct drm_property *prop,
> +					  struct drm_plane *plane,
> +					  struct drm_plane_state *plane_state,
> +					  struct drm_mode_object *obj,
> +					  u64 prop_value, u64 old_val)
> +{
> +	struct drm_mode_config *config = &plane->dev->mode_config;
> +	int ret;
> +
> +	if (prop != config->prop_fb_id &&
> +	    prop != config->prop_in_fence_fd) {
> +		ret = drm_atomic_plane_get_property(plane, plane_state,
> +						    prop, &old_val);
> +		return drm_atomic_check_prop_changes(ret, old_val, prop_value, prop);
> +	}
> +
> +	if (plane_state->plane->type != DRM_PLANE_TYPE_PRIMARY &&
> +	    plane_state->plane->type != DRM_PLANE_TYPE_OVERLAY) {
> +		drm_dbg_atomic(prop->dev,
> +			       "[OBJECT:%d] Only primary or overlay planes can be changed during async flip\n",
> +			       obj->id);
> +		return -EINVAL;
> +	}
> +
> +	return 0;
> +}
> +
>  static const struct drm_plane_funcs dm_plane_funcs = {
>  	.update_plane	= drm_atomic_helper_update_plane,
>  	.disable_plane	= drm_atomic_helper_disable_plane,
> @@ -1438,6 +1466,7 @@ static const struct drm_plane_funcs dm_plane_funcs = {
>  	.atomic_duplicate_state = amdgpu_dm_plane_drm_plane_duplicate_state,
>  	.atomic_destroy_state = amdgpu_dm_plane_drm_plane_destroy_state,
>  	.format_mod_supported = amdgpu_dm_plane_format_mod_supported,
> +	.check_async_props = amdgpu_dm_plane_check_async_props,
>  };
>  
>  int amdgpu_dm_plane_init(struct amdgpu_display_manager *dm,
> -- 
> 2.43.0
> 

-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch