Re: [PATCH v5] amd/display: only require overlay plane to cover whole CRTC on ChromeOS

[Rodrigo Siqueira Jordao <rjordrigo@amd.com>]

On 2021-10-11 11:16 a.m., Simon Ser wrote:
> Commit ddab8bd788f5 ("drm/amd/display: Fix two cursor duplication when
> using overlay") changed the atomic validation code to forbid the
> overlay plane from being used if it doesn't cover the whole CRTC. The
> motivation is that ChromeOS uses the atomic API for everything except
> the cursor plane (which uses the legacy API). Thus amdgpu must always
> be prepared to enable/disable/move the cursor plane at any time without
> failing (or else ChromeOS will trip over).
> 
> As discussed in [1], there's no reason why the ChromeOS limitation
> should prevent other fully atomic users from taking advantage of the
> overlay plane. Let's limit the check to ChromeOS.
> 
> v4: fix ChromeOS detection (Harry)
> 
> v5: fix conflict with linux-next
> 
> [1]: https://lore.kernel.org/amd-gfx/JIQ_93_cHcshiIDsrMU1huBzx9P9LVQxucx8hQArpQu7Wk5DrCl_vTXj_Q20m_L-8C8A5dSpNcSJ8ehfcCrsQpfB5QG_Spn14EYkH9chtg0=@emersion.fr/>> 
> Signed-off-by: Simon Ser <contact@emersion.fr>
> Cc: Alex Deucher <alexander.deucher@amd.com>
> Cc: Harry Wentland <hwentlan@amd.com>
> Cc: Nicholas Kazlauskas <nicholas.kazlauskas@amd.com>
> Cc: Bas Nieuwenhuizen <bas@basnieuwenhuizen.nl>
> Cc: Rodrigo Siqueira <Rodrigo.Siqueira@amd.com>
> Cc: Sean Paul <seanpaul@chromium.org>
> Fixes: ddab8bd788f5 ("drm/amd/display: Fix two cursor duplication when using overlay")
> ---
>   .../gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c | 29 +++++++++++++++++++
>   1 file changed, 29 insertions(+)
> 
> diff --git a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
> index f35561b5a465..2eeda1fec506 100644
> --- a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
> +++ b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
> @@ -10594,6 +10594,31 @@ static int add_affected_mst_dsc_crtcs(struct drm_atomic_state *state, struct drm
>   }
>   #endif
>   
> +static bool is_chromeos(void)
> +{
> +	struct mm_struct *mm = current->mm;
> +	struct file *exe_file;
> +	bool ret;
> +
> +	/* ChromeOS renames its thread to DrmThread. Also check the executable
> +	 * name. */
> +	if (strcmp(current->comm, "DrmThread") != 0 || !mm)
> +		return false;
> +
> +	rcu_read_lock();
> +	exe_file = rcu_dereference(mm->exe_file);
> +	if (exe_file && !get_file_rcu(exe_file))
> +		exe_file = NULL;
> +	rcu_read_unlock();
> +
> +	if (!exe_file)
> +		return false;
> +	ret = strcmp(exe_file->f_path.dentry->d_name.name, "chrome") == 0;
> +	fput(exe_file);
> +
> +	return ret;
> +}
> +
>   static int validate_overlay(struct drm_atomic_state *state)
>   {
>   	int i;
> @@ -10601,6 +10626,10 @@ static int validate_overlay(struct drm_atomic_state *state)
>   	struct drm_plane_state *new_plane_state;
>   	struct drm_plane_state *primary_state, *overlay_state = NULL;
>   
> +	/* This is a workaround for ChromeOS only */
> +	if (!is_chromeos())
> +		return 0;
> +
>   	/* Check if primary plane is contained inside overlay */
>   	for_each_new_plane_in_state_reverse(state, plane, new_plane_state, i) {
>   		if (plane->type == DRM_PLANE_TYPE_OVERLAY) {
> 

Hi Mark,

I tested this patch on ChromeOS, and this can be helpful in two ways:

1. When ChromeOS GUI is running, the workaround for fixing the two 
cursor issues works as expected.
2. When we turn off ChromeOS GUI, this patch also works by making some 
of the overlay tests pass.

I think we should cherry-pick this patch to the ChromeOS tree. Is it ok 
for you?

Thanks
Siqueira