Re: [PATCH] drm/ast: Don't check new mode if CRTC is being disabled

[Emil Velikov <emil.l.velikov@gmail.com>]

Hi Thomas,

Couple of fly-by ideas/suggestions.

On Thu, 30 Apr 2020 at 10:13, Thomas Zimmermann <tzimmermann@suse.de> wrote:
>
> Suspending failed because there's no mode if the CRTC is being
> disabled. Early-out in this case. This fixes runtime PM for ast.
>
> Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
> ---
>  drivers/gpu/drm/ast/ast_mode.c | 3 +++
>  1 file changed, 3 insertions(+)
>
> diff --git a/drivers/gpu/drm/ast/ast_mode.c b/drivers/gpu/drm/ast/ast_mode.c
> index 7a9f20a2fd303..089b7d9a0cf3f 100644
> --- a/drivers/gpu/drm/ast/ast_mode.c
> +++ b/drivers/gpu/drm/ast/ast_mode.c
> @@ -801,6 +801,9 @@ static int ast_crtc_helper_atomic_check(struct drm_crtc *crtc,
>                 return -EINVAL;
Unrelated:
This feels quite dirty. If AST1180 does not support atomic modeset
simply remove the DRIVER_ATOMIC bit.
You can do that at runtime, via drm_device::driver_features in say,
ast_detect_chip()?

The drm_driver::driver_features is immutable, or it ought to be.

>         }
>
> +       if (!state->enable)
> +               return 0; /* no checks required if CRTC is being disabled */
> +
I cannot think of a reason why a driver would need to perform
crtc_atomic_check, if the crtc is being disabled.
Can you spot any? If not, this should be better served in core, which
calls this callback.
Correct?

HTH
-Emil
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