Re: [PATCH v7 01/10] drm/panel: panel-simple: Add missing pm_runtime_dont_use_autosuspend() calls

[Laurent Pinchart <laurent.pinchart@ideasonboard.com>]

Hi Doug,

Thank you for the patch.

On Mon, May 17, 2021 at 01:08:58PM -0700, Douglas Anderson wrote:
> The PM Runtime docs specifically call out the need to call
> pm_runtime_dont_use_autosuspend() in the remove() callback if
> pm_runtime_use_autosuspend() was called in probe():
> 
> > Drivers in ->remove() callback should undo the runtime PM changes done
> > in ->probe(). Usually this means calling pm_runtime_disable(),
> > pm_runtime_dont_use_autosuspend() etc.

~/src/kernel/linux $ git grep pm_runtime_use_autosuspend -- drivers | wc -l
209
~/src/kernel/linux $ git grep pm_runtime_dont_use_autosuspend -- drivers | wc -l
80

Seems like a lost battle :-(

The fix is right, but I wonder if this shouldn't be handled
automatically by the runtime PM core. The runtime PM API is notoriously
difficult to use correctly.

> We should do this. This fixes a warning splat that I saw when I was
> testing out the panel-simple's remove().
>
> Fixes: 3235b0f20a0a ("drm/panel: panel-simple: Use runtime pm to avoid excessive unprepare / prepare")
> Signed-off-by: Douglas Anderson <dianders@chromium.org>

Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>

> ---
> 
> Changes in v7:
> - pm_runtime_dont_use_autosuspend() fix new for v7.
> 
>  drivers/gpu/drm/panel/panel-simple.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/drivers/gpu/drm/panel/panel-simple.c b/drivers/gpu/drm/panel/panel-simple.c
> index 9be050ab372f..21939d4352cf 100644
> --- a/drivers/gpu/drm/panel/panel-simple.c
> +++ b/drivers/gpu/drm/panel/panel-simple.c
> @@ -798,6 +798,7 @@ static int panel_simple_probe(struct device *dev, const struct panel_desc *desc)
>  	return 0;
>  
>  disable_pm_runtime:
> +	pm_runtime_dont_use_autosuspend(dev);
>  	pm_runtime_disable(dev);
>  free_ddc:
>  	if (panel->ddc)
> @@ -814,6 +815,7 @@ static int panel_simple_remove(struct device *dev)
>  	drm_panel_disable(&panel->base);
>  	drm_panel_unprepare(&panel->base);
>  
> +	pm_runtime_dont_use_autosuspend(dev);
>  	pm_runtime_disable(dev);
>  	if (panel->ddc)
>  		put_device(&panel->ddc->dev);

-- 
Regards,

Laurent Pinchart