Re: [PATCH 3/3] drm/atomic: Try to preserve the crtc enabled state in drm_atomic_remove_fb.

[Sean Paul <seanpaul@chromium.org>]

On Tue, Feb 21, 2017 at 02:51:42PM +0100, Maarten Lankhorst wrote:
> This introduces a slight behavioral change to rmfb. Instead of
> disabling a crtc when the primary plane is disabled, we try to
> preserve it.
> 
> Apart from old versions of the vmwgfx xorg driver, there is
> nothing depending on rmfb disabling a crtc. Since vmwgfx is
> a legacy driver we can safely only disable the plane with atomic.
> In the conversion to atomic the driver will reject the config
> without primary plane.
> 
> If this commit is rejected by the driver then we will still fall
> back to the old behavior and turn off the crtc.
> 
> Signed-off-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
> ---
>  drivers/gpu/drm/drm_atomic.c | 22 ++++++++++++++++++++--
>  1 file changed, 20 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/drm_atomic.c b/drivers/gpu/drm/drm_atomic.c
> index 285e1c23e8c9..0d5b0065208e 100644
> --- a/drivers/gpu/drm/drm_atomic.c
> +++ b/drivers/gpu/drm/drm_atomic.c
> @@ -2070,7 +2070,7 @@ int drm_atomic_remove_fb(struct drm_framebuffer *fb)
>  	struct drm_connector *conn;
>  	struct drm_connector_state *conn_state;
>  	int i, ret = 0;
> -	unsigned plane_mask;
> +	unsigned plane_mask, disable_crtcs = false;
>  
>  	state = drm_atomic_state_alloc(dev);
>  	if (!state)
> @@ -2097,7 +2097,13 @@ int drm_atomic_remove_fb(struct drm_framebuffer *fb)
>  			goto unlock;
>  		}
>  
> -		if (plane_state->crtc->primary == plane) {
> +		/*
> +		 * Some drivers do not support keeping crtc active with the
> +		 * primary plane disabled. If we fail to commit with -EINVAL
> +		 * then we will try to perform the same commit but with all
> +		 * crtc's disabled for primary planes as well.
> +		 */
> +		if (disable_crtcs && plane_state->crtc->primary == plane) {
>  			struct drm_crtc_state *crtc_state;
>  
>  			crtc_state = drm_atomic_get_existing_crtc_state(state, plane_state->crtc);
> @@ -2122,6 +2128,7 @@ int drm_atomic_remove_fb(struct drm_framebuffer *fb)
>  		plane->old_fb = plane->fb;
>  	}
>  
> +	/* This list is only not empty when disable_crtcs is set. */
>  	for_each_connector_in_state(state, conn, conn_state, i) {
>  		ret = drm_atomic_set_crtc_for_connector(conn_state, NULL);
>  
> @@ -2143,6 +2150,17 @@ int drm_atomic_remove_fb(struct drm_framebuffer *fb)
>  
>  	drm_atomic_state_put(state);
>  
> +	if (ret == -EINVAL && !disable_crtcs) {
> +		disable_crtcs = true;
> +
> +		state = drm_atomic_state_alloc(dev);
> +		if (state) {
> +			state->acquire_ctx = &ctx;
> +			goto retry;

Re-using the retry label is a little fishy here. You need to re-allocate state,
but we don't drop the locks, which makes things a little unbalanced (I realize
modeset_lock will s/EALREADY/0/).

Perhaps something like this above would be more clear:

+       drm_modeset_acquire_init(&ctx, 0);
+retry:
+       plane_mask = 0;
+       ret = drm_modeset_lock_all_ctx(dev, &ctx);
+       if (ret)
+               goto unlock;
+
+retry_disable:
+       state = drm_atomic_state_alloc(dev);
+       if (!state)
+               return -ENOMEM;
+       state->acquire_ctx = &ctx;
+

Then you can do:


+	if (ret == -EINVAL && !disable_crtcs) {
+		disable_crtcs = true;
+		goto retry_disable;
+       }

(you would also need to ensure you moved the state_put above the EDEADLK
handling).

Thoughts?

Sean

> +		}
> +		ret = -ENOMEM;
> +	}
> +
>  	drm_modeset_drop_locks(&ctx);
>  	drm_modeset_acquire_fini(&ctx);
>  
> -- 
> 2.7.4
> 
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-- 
Sean Paul, Software Engineer, Google / Chromium OS
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