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

[Boris Brezillon]

On Fri, 11 Oct 2019 15:54:53 +0200
Andrzej Hajda <a.hajda at samsung.com> wrote:

> 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.

Then I was wrong :-).

> 
> 
> >  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.

You mean call
drm_connector_set_link_status_property(DRM_MODE_LINK_STATUS_BAD) ?

> 
> 
> > 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.

I'm fine with that. Thierry, Sam, any opinion?