Re: [PATCH 1/7] drm/arc: Stop consulting plane->fb

["Ville Syrjälä" <ville.syrjala@linux.intel.com>]

On Thu, Apr 05, 2018 at 10:08:57PM +0200, Daniel Vetter wrote:
> On Thu, Apr 05, 2018 at 10:50:29PM +0300, Ville Syrjala wrote:
> > From: Ville Syrjälä <ville.syrjala@linux.intel.com>
> > 
> > We want to stop using plane->fb with atomic driver, so stop looking at
> > it.
> > 
> > I have no idea what this code is trying to achieve. There is no
> > corresponding check in the enable path. Also since
> > arc_pgu_set_pxl_fmt() will anyway oops if there is no fb I'm going
> > to assuming that I can just remove the check entirely. There seems
> > to be a general shortage of .atomic_check() in this driver...
> 
> I think arcpgu is the perfect example of a small driver that _really_
> wants to use drm_simple_display_pipe_helper. Which would address the
> outright lack of any and all atomic_check code (beyond basic mode
> validation through mode_valid).
> 
> I also just noticed that it still has a bunch of the legacy hooks set,
> e.g. mode_set, mode_set_base are all no longer used in atomic.
> 
> I think the code won't be able to oops, since if there's no fb, we don't
> enable the plane (and it happily allows that), so should be all
> non-oopsing. Even with this check here removed.

arc_pgu_set_pxl_fmt() gets called from the .mode_set_nofb() hook
which I assume doesn't care about planes at all. So to me it looks like
it'll definitely oops.

> 
> Ofc the hw might get pissed at us in this case, but I can't tell that.
> Like I said, conversion to drm_simple_display_pipe_helper is probably the
> way to go.
> 
> Anyway, this patch here looks good, if you adjust the commit message to
> explain why it can't oops:
> 
> Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
> 
> > 
> > Cc: Alexey Brodkin <abrodkin@synopsys.com>
> > Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
> > Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
> > ---
> >  drivers/gpu/drm/arc/arcpgu_crtc.c | 3 ---
> >  1 file changed, 3 deletions(-)
> > 
> > diff --git a/drivers/gpu/drm/arc/arcpgu_crtc.c b/drivers/gpu/drm/arc/arcpgu_crtc.c
> > index 16903dc7fe0d..c3349b8fb58b 100644
> > --- a/drivers/gpu/drm/arc/arcpgu_crtc.c
> > +++ b/drivers/gpu/drm/arc/arcpgu_crtc.c
> > @@ -136,9 +136,6 @@ static void arc_pgu_crtc_atomic_disable(struct drm_crtc *crtc,
> >  {
> >  	struct arcpgu_drm_private *arcpgu = crtc_to_arcpgu_priv(crtc);
> >  
> > -	if (!crtc->primary->fb)
> > -		return;
> > -
> >  	clk_disable_unprepare(arcpgu->clk);
> >  	arc_pgu_write(arcpgu, ARCPGU_REG_CTRL,
> >  			      arc_pgu_read(arcpgu, ARCPGU_REG_CTRL) &
> > -- 
> > 2.16.1
> > 
> 
> -- 
> Daniel Vetter
> Software Engineer, Intel Corporation
> http://blog.ffwll.ch

-- 
Ville Syrjälä
Intel OTC
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