Re: [PATCH v2] drm/loongson: stop to set get_vblank_timestamp for LS7A1000 CRTC

[Thomas Zimmermann <tzimmermann@suse.de>]

Hi

Am 23.03.26 um 12:42 schrieb Icenowy Zheng:
[...]
>>> drm_update_vblank_count+0xac/0x418
>>> [    0.334960] [<ffffffff80be6270>] drm_vblank_enable+0xf0/0x288
>>> [    0.334960] [<ffffffff80be7010>] drm_vblank_get+0xf8/0x160
>>> [    0.334960] [<ffffffff80beb2e0>]
>>> drm_client_modeset_wait_for_vblank+0x50/0xa0
> I doubt the problem here is that the function above is called with
> hardcoded 0 by drm_fb_helper_fb_dirty() (being inlined into
> drm_fb_helper_damage_work() by the compiler). Then on my setup it
> failed because my primary output (laptop LCD) is on CRTC 1 (CRTC 0 is
> external HDMI instead).

The CRTC 0 has vblank interrupt. The CRTC 1 does not. Is that correct?

>
> This is new behavior introduced by d8c4bddcd8bc ("drm/fb-helper:
> Synchronize dirty worker with vblank"), and the commit messages say
> `This allows several screen updates to pile up and acts as a rate
> limiter.` .

This should work if the vblanks are configured correctly.


>
> Should it wait for any vblanks instead of waiting for one on CRTC 0 ?
> (Or check whether CRTC 0 is on before waiting on it?)

It should only wait for the vblank on the CRTC it uses (1 in your case).

Best regards
Thomas


>
> Thanks,
> Icenowy
>
>>> [    0.334960] [<ffffffff80c0a144>]
>>> drm_fb_helper_damage_work+0x8c/0x1d8
>>> [    0.334960] [<ffffffff8028fac8>] process_one_work+0x198/0x348
>>> [    0.334960] [<ffffffff802906c0>] worker_thread+0x238/0x390
>>> [    0.334960] [<ffffffff8029c0d8>] kthread+0x160/0x198
>>> [    0.334960] [<ffffffff8021fd8c>]
>>> ret_from_kernel_thread+0x14/0x1c
>>>
>>> [    0.334960] ---[ end trace 0000000000000000 ]---
>>> ```
>>>
>>>>>> Signed-off-by: Icenowy Zheng <zhengxingda@iscas.ac.cn>
>>>>> Oh forgot to attach when crafting v2:
>>>>>
>>>>> ```
>>>>> Acked-by: Thomas Zimmermann <tzimmermann@suse.de>
>>>>> ```
>>>>>
>>>>>> ---
>>>>>> Changes in v2:
>>>>>> - Re-formatted Loongson product model numbers per request
>>>>>> from
>>>>>> Huacai.
>>>>>>
>>>>>>     drivers/gpu/drm/loongson/lsdc_crtc.c | 1 -
>>>>>>     1 file changed, 1 deletion(-)
>>>>>>
>>>>>> diff --git a/drivers/gpu/drm/loongson/lsdc_crtc.c
>>>>>> b/drivers/gpu/drm/loongson/lsdc_crtc.c
>>>>>> index 587fbe285e9ef..b3af8e0cdb15f 100644
>>>>>> --- a/drivers/gpu/drm/loongson/lsdc_crtc.c
>>>>>> +++ b/drivers/gpu/drm/loongson/lsdc_crtc.c
>>>>>> @@ -721,7 +721,6 @@ static const struct drm_crtc_funcs
>>>>>> ls7a1000_crtc_funcs = {
>>>>>>     	.late_register = lsdc_crtc_late_register,
>>>>>>     	.enable_vblank = lsdc_crtc_enable_vblank,
>>>>>>     	.disable_vblank = lsdc_crtc_disable_vblank,
>>>>>> -	.get_vblank_timestamp =
>>>>>> drm_crtc_vblank_helper_get_vblank_timestamp,
>>>>>>     	.atomic_print_state = lsdc_crtc_atomic_print_state,
>>>>>>     };
>>>>>>     

-- 
--
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)