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

[robin.murphy@arm.com (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@arm.com>
>> Signed-off-by: Robin Murphy <robin.murphy@arm.com>
>> ---
>>   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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>