Re: [PATCH 2/2] drm: hdlcd: Suspend/resume only active crtcs

[Robin Murphy]

Hi Daniel,

On 05/05/16 18:06, Daniel Vetter wrote:
> On Thu, May 05, 2016 at 05:13:38PM +0100, Robin Murphy wrote:
> > The current PM ops simply unconditionally enable/disable the HDLCD,
> > which proves problematic when there is no display plugged in - since
> > without a crtc the hardware itself is still in an uninitialised state,
> > coming out of suspend results in it being enabled without a valid
> > framebuffer address, which typically results in it trying to scan out
> > from bus address 0 and flooding the system with error interrupts.
> >
> > Fix this by checking the crtc state on resume, and only enabling the
> > hardware if it's actually supposed to be. For the sake of consistency,
> > do the same on the suspend path as well, although there it's merely a
> > case of skipping unnecessary work.
> >
> > CC: Liviu Dudau <liviu.dudau@xxxxxxx>
> > Signed-off-by: Robin Murphy <robin.murphy@xxxxxxx>
> > ---
> >   drivers/gpu/drm/arm/hdlcd_crtc.c | 6 ++++--
> >   1 file changed, 4 insertions(+), 2 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/arm/hdlcd_crtc.c b/drivers/gpu/drm/arm/hdlcd_crtc.c
> > index fef1b04c2aab..bf6ff5e48adc 100644
> > --- a/drivers/gpu/drm/arm/hdlcd_crtc.c
> > +++ b/drivers/gpu/drm/arm/hdlcd_crtc.c
> > @@ -296,12 +296,14 @@ static struct drm_plane *hdlcd_plane_init(struct drm_device *drm)
> >
> >   void hdlcd_crtc_suspend(struct drm_crtc *crtc)
> >   {
> > -	hdlcd_crtc_disable(crtc);
> > +	if (crtc->state->active)
> > +		hdlcd_crtc_disable(crtc);
> >   }
> >
> >   void hdlcd_crtc_resume(struct drm_crtc *crtc)
> >   {
> > -	hdlcd_crtc_enable(crtc);
> > +	if (crtc->state->active)
> > +		hdlcd_crtc_enable(crtc);
> >   }
>
> If you use the atomic helpers to suspend/resume your entire display
> pipeline these callbacks shouldn't even be needed at all. Tried just
> removing them?

I'll have to leave that in Liviu's hands as I know literally nothing 
about the relationship between platform PM ops and DRM helpers ;)
My only motivation is for the arm64 hibernate support currently sat in 
-next for 4.7 to stop being broken on my Juno board by this.

Robin.

> -Daniel
>
> >   int hdlcd_setup_crtc(struct drm_device *drm)
> > --
> > 2.8.1.dirty
> >
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