[PATCH v2 04/21] drm/exynos: Fix potential unbalanced calls to pm_runtime_put

[Andrzej Hajda]

On 26.08.2019 17:26, Boris Brezillon wrote:
> The encoder->enable() can't report errors and is expected to always
> succeed. If we call pm_runtime_put() in the exynos_dsi_enable() error
> path (as currently done) we'll have unbalanced get/put calls when
> encoder->disable() is called.


True


>
> The situation is not ideal since drm_panel_{prepare,enable}() can
> theoretically return an error (even if in practice I don't think any
> panel driver does that).


So why do you want to fix it at all, if you think return value is always
0 :) ?


git grep -p -A30 '_prepare' drivers/gpu/drm/panel/ shows that many of
them can return errors.


>  Putting a WARN_ON() is the best we can do,
> unfortunately.


I guess optimally we should use DRM_MODE_LINK_STATUS_BAD, but I am not
sure how exactly it should be handled.


> Note that -ENOSYS is actually a valid case, it just
> means the panel driver does not implement the hook.


It would be good then to fix it in panel framework, ie without hook
drm_panel_* function should return 0, ENOSYS makes no sense here.


Regards

Andrzej


>
> Signed-off-by: Boris Brezillon <boris.brezillon at collabora.com>
> ---
> Changes in v2:
> * New patch
> ---
>  drivers/gpu/drm/exynos/exynos_drm_dsi.c | 14 ++------------
>  1 file changed, 2 insertions(+), 12 deletions(-)
>
> diff --git a/drivers/gpu/drm/exynos/exynos_drm_dsi.c b/drivers/gpu/drm/exynos/exynos_drm_dsi.c
> index 8e655ae1fb0c..c555cecfe1f5 100644
> --- a/drivers/gpu/drm/exynos/exynos_drm_dsi.c
> +++ b/drivers/gpu/drm/exynos/exynos_drm_dsi.c
> @@ -1387,8 +1387,7 @@ static void exynos_dsi_enable(struct drm_encoder *encoder)
>  
>  	if (dsi->panel) {
>  		ret = drm_panel_prepare(dsi->panel);
> -		if (ret < 0)
> -			goto err_put_sync;
> +		WARN_ON(ret && ret != -ENOSYS);
>  	} else {
>  		drm_bridge_pre_enable(dsi->out_bridge);
>  	}
> @@ -1398,22 +1397,13 @@ static void exynos_dsi_enable(struct drm_encoder *encoder)
>  
>  	if (dsi->panel) {
>  		ret = drm_panel_enable(dsi->panel);
> -		if (ret < 0)
> -			goto err_display_disable;
> +		WARN_ON(ret && ret != -ENOSYS);
>  	} else {
>  		drm_bridge_enable(dsi->out_bridge);
>  	}
>  
>  	dsi->state |= DSIM_STATE_VIDOUT_AVAILABLE;
>  	return;
> -
> -err_display_disable:
> -	exynos_dsi_set_display_enable(dsi, false);
> -	drm_panel_unprepare(dsi->panel);
> -
> -err_put_sync:
> -	dsi->state &= ~DSIM_STATE_ENABLED;
> -	pm_runtime_put(dsi->dev);
>  }
>  
>  static void exynos_dsi_disable(struct drm_encoder *encoder)