[Intel-gfx] [RFC][PATCH 07/11] drm/probe-helper: Avoid iterating the list twice on ww backoff

[Ville Syrjälä]

On Tue, Mar 06, 2018 at 10:49:43AM +0100, Daniel Vetter wrote:
> On Tue, Feb 27, 2018 at 02:56:56PM +0200, Ville Syrjala wrote:
> > From: Ville Syrjälä <ville.syrjala at linux.intel.com>
> > 
> > If we have to backoff there's no point in going over the mode list again
> > to mark all the modes as stale. We can defer that until we're ready to
> > refresh the mode list. Avoids multiple list walks if we have to do the
> > locking backoff.
> > 
> > Cc: Keith Packard <keithp at keithp.com>
> > Cc: Daniel Vetter <daniel.vetter at ffwll.ch>
> > Signed-off-by: Ville Syrjälä <ville.syrjala at linux.intel.com>
> 
> Some drivers add modes from their ->detect callbacks I think, won't this
> break them? At least I'm never sure about what different drivers are
> supposed to do in each case.
> 
> Otoh the kerneldoc is fairly clear, and this patch is easy to revert, and
> it might help in forcing drivers to be more consistent.

Hmm. Yeah I didn't actually make sure that drivers aren't adding stuff
to the ->modes list directly. They shouldn't but who knows.

> 
> If you add a note about my concerns (as a hint in case we bisect a
> regression to this patch), then this is:

Sure, I'll try to add something.

> 
> Reviewed-by: Daniel Vetter <daniel.vetter at ffwll.ch>
> 
> 
> > ---
> >  drivers/gpu/drm/drm_probe_helper.c | 8 ++++----
> >  1 file changed, 4 insertions(+), 4 deletions(-)
> > 
> > diff --git a/drivers/gpu/drm/drm_probe_helper.c b/drivers/gpu/drm/drm_probe_helper.c
> > index 527743394150..7dc7e635d7e4 100644
> > --- a/drivers/gpu/drm/drm_probe_helper.c
> > +++ b/drivers/gpu/drm/drm_probe_helper.c
> > @@ -415,10 +415,6 @@ int drm_helper_probe_single_connector_modes(struct drm_connector *connector,
> >  	} else
> >  		WARN_ON(ret < 0);
> >  
> > -	/* set all old modes to the stale state */
> > -	list_for_each_entry(mode, &connector->modes, head)
> > -		mode->status = MODE_STALE;
> > -
> >  	old_status = connector->status;
> >  
> >  	if (connector->force) {
> > @@ -472,6 +468,10 @@ int drm_helper_probe_single_connector_modes(struct drm_connector *connector,
> >  
> >  	dev->mode_config.poll_running = drm_kms_helper_poll;
> >  
> > +	/* set all old modes to the stale state */
> > +	list_for_each_entry(mode, &connector->modes, head)
> > +		mode->status = MODE_STALE;
> > +
> >  	if (connector->status == connector_status_disconnected) {
> >  		DRM_DEBUG_KMS("[CONNECTOR:%d:%s] disconnected\n",
> >  			connector->base.id, connector->name);
> > -- 
> > 2.13.6
> > 
> 
> -- 
> Daniel Vetter
> Software Engineer, Intel Corporation
> http://blog.ffwll.ch

-- 
Ville Syrjälä
Intel OTC