Re: [PATCH 7/7] drm/panel: make prepare/enable and disable/unprepare calls return void

[Neil Armstrong <neil.armstrong@linaro.org>]

On 01/04/2025 07:11, Dmitry Baryshkov wrote:
> Now there are no users of the return value of the drm_panel_prepare(),
> drm_panel_unprepare(), drm_panel_enable() and drm_panel_disable() calls.
> Usually these calls are performed from the atomic callbacks, where it is
> impossible to return an error. Stop returning error codes and return
> void instead.
> 
> Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@oss.qualcomm.com>
> ---
>   drivers/gpu/drm/drm_panel.c                     | 54 +++++++++----------------
>   drivers/gpu/drm/panel/panel-newvision-nv3051d.c |  9 +----
>   include/drm/drm_panel.h                         |  8 ++--
>   3 files changed, 26 insertions(+), 45 deletions(-)
> 
> diff --git a/drivers/gpu/drm/drm_panel.c b/drivers/gpu/drm/drm_panel.c
> index c627e42a7ce70459f50eb5095fffc806ca45dabf..faa7a76b63b53b3a45b3400d8bf3b58a027a340e 100644
> --- a/drivers/gpu/drm/drm_panel.c
> +++ b/drivers/gpu/drm/drm_panel.c
> @@ -105,21 +105,21 @@ EXPORT_SYMBOL(drm_panel_remove);
>    *
>    * Calling this function will enable power and deassert any reset signals to
>    * the panel. After this has completed it is possible to communicate with any
> - * integrated circuitry via a command bus.
> - *
> - * Return: 0 on success or a negative error code on failure.
> + * integrated circuitry via a command bus. This function cannot fail (as it is
> + * called from the pre_enable call chain). There will always be a call to
> + * drm_panel_disable() afterwards.
>    */
> -int drm_panel_prepare(struct drm_panel *panel)
> +void drm_panel_prepare(struct drm_panel *panel)
>   {
>   	struct drm_panel_follower *follower;
>   	int ret;
>   
>   	if (!panel)
> -		return -EINVAL;
> +		return;
>   
>   	if (panel->prepared) {
>   		dev_warn(panel->dev, "Skipping prepare of already prepared panel\n");
> -		return 0;
> +		return;
>   	}
>   
>   	mutex_lock(&panel->follower_lock);
> @@ -138,11 +138,8 @@ int drm_panel_prepare(struct drm_panel *panel)
>   				 follower->funcs->panel_prepared, ret);
>   	}
>   
> -	ret = 0;
>   exit:
>   	mutex_unlock(&panel->follower_lock);
> -
> -	return ret;
>   }
>   EXPORT_SYMBOL(drm_panel_prepare);
>   
> @@ -154,16 +151,14 @@ EXPORT_SYMBOL(drm_panel_prepare);
>    * reset, turn off power supplies, ...). After this function has completed, it
>    * is usually no longer possible to communicate with the panel until another
>    * call to drm_panel_prepare().
> - *
> - * Return: 0 on success or a negative error code on failure.
>    */
> -int drm_panel_unprepare(struct drm_panel *panel)
> +void drm_panel_unprepare(struct drm_panel *panel)
>   {
>   	struct drm_panel_follower *follower;
>   	int ret;
>   
>   	if (!panel)
> -		return -EINVAL;
> +		return;
>   
>   	/*
>   	 * If you are seeing the warning below it likely means one of two things:
> @@ -176,7 +171,7 @@ int drm_panel_unprepare(struct drm_panel *panel)
>   	 */
>   	if (!panel->prepared) {
>   		dev_warn(panel->dev, "Skipping unprepare of already unprepared panel\n");
> -		return 0;
> +		return;
>   	}
>   
>   	mutex_lock(&panel->follower_lock);
> @@ -195,11 +190,8 @@ int drm_panel_unprepare(struct drm_panel *panel)
>   	}
>   	panel->prepared = false;
>   
> -	ret = 0;
>   exit:
>   	mutex_unlock(&panel->follower_lock);
> -
> -	return ret;
>   }
>   EXPORT_SYMBOL(drm_panel_unprepare);
>   
> @@ -209,26 +201,26 @@ EXPORT_SYMBOL(drm_panel_unprepare);
>    *
>    * Calling this function will cause the panel display drivers to be turned on
>    * and the backlight to be enabled. Content will be visible on screen after
> - * this call completes.
> - *
> - * Return: 0 on success or a negative error code on failure.
> + * this call completes. This function cannot fail (as it is called from the
> + * enable call chain). There will always be a call to drm_panel_disable()
> + * afterwards.
>    */
> -int drm_panel_enable(struct drm_panel *panel)
> +void drm_panel_enable(struct drm_panel *panel)
>   {
>   	int ret;
>   
>   	if (!panel)
> -		return -EINVAL;
> +		return;
>   
>   	if (panel->enabled) {
>   		dev_warn(panel->dev, "Skipping enable of already enabled panel\n");
> -		return 0;
> +		return;
>   	}
>   
>   	if (panel->funcs && panel->funcs->enable) {
>   		ret = panel->funcs->enable(panel);
>   		if (ret < 0)
> -			return ret;
> +			return;
>   	}
>   	panel->enabled = true;
>   
> @@ -236,8 +228,6 @@ int drm_panel_enable(struct drm_panel *panel)
>   	if (ret < 0)
>   		DRM_DEV_INFO(panel->dev, "failed to enable backlight: %d\n",
>   			     ret);
> -
> -	return 0;
>   }
>   EXPORT_SYMBOL(drm_panel_enable);
>   
> @@ -248,15 +238,13 @@ EXPORT_SYMBOL(drm_panel_enable);
>    * This will typically turn off the panel's backlight or disable the display
>    * drivers. For smart panels it should still be possible to communicate with
>    * the integrated circuitry via any command bus after this call.
> - *
> - * Return: 0 on success or a negative error code on failure.
>    */
> -int drm_panel_disable(struct drm_panel *panel)
> +void drm_panel_disable(struct drm_panel *panel)
>   {
>   	int ret;
>   
>   	if (!panel)
> -		return -EINVAL;
> +		return;
>   
>   	/*
>   	 * If you are seeing the warning below it likely means one of two things:
> @@ -269,7 +257,7 @@ int drm_panel_disable(struct drm_panel *panel)
>   	 */
>   	if (!panel->enabled) {
>   		dev_warn(panel->dev, "Skipping disable of already disabled panel\n");
> -		return 0;
> +		return;
>   	}
>   
>   	ret = backlight_disable(panel->backlight);
> @@ -280,11 +268,9 @@ int drm_panel_disable(struct drm_panel *panel)
>   	if (panel->funcs && panel->funcs->disable) {
>   		ret = panel->funcs->disable(panel);
>   		if (ret < 0)
> -			return ret;
> +			return;
>   	}
>   	panel->enabled = false;
> -
> -	return 0;
>   }
>   EXPORT_SYMBOL(drm_panel_disable);
>   
> diff --git a/drivers/gpu/drm/panel/panel-newvision-nv3051d.c b/drivers/gpu/drm/panel/panel-newvision-nv3051d.c
> index 5d115ecd5dd44c8e5e7d1fb8afe573324e987f59..b6429795e8f518646443dd8179f3ec28cef4dc0f 100644
> --- a/drivers/gpu/drm/panel/panel-newvision-nv3051d.c
> +++ b/drivers/gpu/drm/panel/panel-newvision-nv3051d.c
> @@ -413,15 +413,10 @@ static int panel_nv3051d_probe(struct mipi_dsi_device *dsi)
>   static void panel_nv3051d_shutdown(struct mipi_dsi_device *dsi)
>   {
>   	struct panel_nv3051d *ctx = mipi_dsi_get_drvdata(dsi);
> -	int ret;
>   
> -	ret = drm_panel_unprepare(&ctx->panel);
> -	if (ret < 0)
> -		dev_err(&dsi->dev, "Failed to unprepare panel: %d\n", ret);
> +	drm_panel_unprepare(&ctx->panel);
>   
> -	ret = drm_panel_disable(&ctx->panel);
> -	if (ret < 0)
> -		dev_err(&dsi->dev, "Failed to disable panel: %d\n", ret);
> +	drm_panel_disable(&ctx->panel);
>   }
>   
>   static void panel_nv3051d_remove(struct mipi_dsi_device *dsi)
> diff --git a/include/drm/drm_panel.h b/include/drm/drm_panel.h
> index a9c042c8dea1a82ef979c7a68204e0b55483fc28..18bf338c8b96254dc3f2880106b944e71ea4c9a7 100644
> --- a/include/drm/drm_panel.h
> +++ b/include/drm/drm_panel.h
> @@ -275,11 +275,11 @@ void drm_panel_init(struct drm_panel *panel, struct device *dev,
>   void drm_panel_add(struct drm_panel *panel);
>   void drm_panel_remove(struct drm_panel *panel);
>   
> -int drm_panel_prepare(struct drm_panel *panel);
> -int drm_panel_unprepare(struct drm_panel *panel);
> +void drm_panel_prepare(struct drm_panel *panel);
> +void drm_panel_unprepare(struct drm_panel *panel);
>   
> -int drm_panel_enable(struct drm_panel *panel);
> -int drm_panel_disable(struct drm_panel *panel);
> +void drm_panel_enable(struct drm_panel *panel);
> +void drm_panel_disable(struct drm_panel *panel);
>   
>   int drm_panel_get_modes(struct drm_panel *panel, struct drm_connector *connector);
>   
> 

LGTM

Reviewed-by: Neil Armstrong <neil.armstrong@linaro.org>