Re: [PATCH] drm/client: check whether CRTC is active before waiting for vblank

[Thomas Zimmermann <tzimmermann@suse.de>]

Hi

Am 22.05.26 um 15:28 schrieb Ville Syrjälä:
[...]
>>>> But why does your HW use CRTC 1 in the first place.
>>> Could be eg. the enabled outputs can't be driven with CRTC 0.
>>>
>>> I guess what you want to do is pick the first crtc from modesets[]
>>> which is enabled. Or perhaps even "pick the Nth enabled crtc from
>>> modesets[] based on the ioctl argument".
>> The enable-status of each CRTC could change later on, which might lead
>> to problems.
> Sound like a locking issue if someone is changing the configuration
> at the same time we're trying to do the vblank wait here.

I mean that the connected outputs could change at a later point or we 
could have multiple CRTCs in use. Today, someone in #intel-gfx reported 
a problem with panning if multiple CRTCs are in use.

Therefore picking a CRTC freely could be a problem. Let's say we 
configure modes from one CRTC, but later wait/pan/flush with another 
CRTC. I would not trust this to work correctly.

Hence, my suggestion is to select a primary CRTC during the fbdev 
client's probe and use it for all later operations until the next probe 
happens.  All other CRTCs would mirror the primary one.

Best regards
Thomas


>
>> Picking the one CRTC/output with the lowest spec and
>> mirroring it to the others might work. This CRTC would then be the one
>> to wait for.
>>
>> Best regards
>> Thomas
>>
>> -- 
>> --
>> Thomas Zimmermann
>> Graphics Driver Developer
>> SUSE Software Solutions Germany GmbH
>> Frankenstr. 146, 90461 Nürnberg, Germany, www.suse.com
>> GF: Jochen Jaser, Andrew McDonald, Werner Knoblich, (HRB 36809, AG Nürnberg)
>>

-- 
--
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Frankenstr. 146, 90461 Nürnberg, Germany, www.suse.com
GF: Jochen Jaser, Andrew McDonald, Werner Knoblich, (HRB 36809, AG Nürnberg)