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

[Jianmin Lv]

On 2026/3/21 下午5:29, Icenowy Zheng wrote:
> 在 2026-03-21六的 17:28 +0800，Icenowy Zheng写道：
> > As there's no known hardware capability about querying vblank on the
> > LS7A1000 display controller, setting get_vblank_timestamp will
> > mislead the
> > kernel about the support of DC-backed high precision vblank query.
> >
> > Drop this function pointer in the CRTC function table for LS7A1000.
> >
> > This solves a kernel warning when booting Linux 7.0-rc3 on a
> > Loongson-3A4000+LS7A1000 Haier Boyue G51 laptop (with injected EDID
> > for
> > replicating the display timing set by the firmware).
The drm_crtc_vblank_helper_get_vblank_timestamp will call 
get_scanout_position hook to caculate timestamp, and the driver has 
get_scanout_position to support it (LS7A1000 has related register). So 
the get_vblank_timestamp hook is ok for LS7A1000, and we'd better look 
into the warning information.

> > Signed-off-by: Icenowy Zheng <zhengxingda@xxxxxxxxxxx>
>
> Oh forgot to attach when crafting v2:
>
> ```
> Acked-by: Thomas Zimmermann <tzimmermann@xxxxxxx>
> ```
>
> > ---
> > 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,
> >   };
> >