RE: [PATCH 12/14] drm/i915/dsb: Clear DSB_ENABLE_DEWAKE once the DSB is done

[Manna, Animesh]

> -Original Message-
> From: Intel-gfx  On Behalf Of Ville
> Syrjala
> Sent: Tuesday, June 25, 2024 12:41 AM
> To: intel-gfx@lists.freedesktop.org
> Subject: [PATCH 12/14] drm/i915/dsb: Clear DSB_ENABLE_DEWAKE once the
> DSB is done
> 
> From: Ville Syrjälä 
> 
> In order to avoid the DSB keeping the DEwake permanently asserted we
> must clear DSB_PMCTRL_2.DSB_FORCE_DEWAKE once we are done. For
> good measure do the same for DSB_PMCTRL.DSB_ENABLE_DEWAKE.
> 
> Experimentally this doens't seem to be actually necessary (unlike with
> DSB_FORCE_DEWAKE). That is, the DSB_ENABLE_DEWAKE doesn't seem to
> do anything whenever the DSB is not active.
> But I'd hate to waste a ton of power in case there I'm wrong and there is
> some way DEwake could remaing asserted. One extra register write is a small
> price to pay for some peace of mind.
> 
> Signed-off-by: Ville Syrjälä 

Reviewed-by: Animesh Manna 

> ---
>  drivers/gpu/drm/i915/display/intel_dsb.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/i915/display/intel_dsb.c
> b/drivers/gpu/drm/i915/display/intel_dsb.c
> index cf710f0bf430..fad37e7856b1 100644
> --- a/drivers/gpu/drm/i915/display/intel_dsb.c
> +++ b/drivers/gpu/drm/i915/display/intel_dsb.c
> @@ -464,8 +464,10 @@ void intel_dsb_finish(struct intel_dsb *dsb)
>   /*
>* DSB_FORCE_DEWAKE remains active even after DSB is
>* disabled, so make sure to clear it (if set during
> -  * intel_dsb_commit()).
> +  * intel_dsb_commit()). And clear DSB_ENABLE_DEWAKE as
> +  * well for good measure.
>*/
> + intel_dsb_reg_write(dsb, DSB_PMCTRL(crtc->pipe, dsb->id), 0);
>   intel_dsb_reg_write_masked(dsb, DSB_PMCTRL_2(crtc->pipe, dsb-
> >id),
>  DSB_FORCE_DEWAKE, 0);
> 
> --
> 2.44.2

[PATCH 12/14] drm/i915/dsb: Clear DSB_ENABLE_DEWAKE once the DSB is done

[Ville Syrjala]

From: Ville Syrjälä 

In order to avoid the DSB keeping the DEwake permanently
asserted we must clear DSB_PMCTRL_2.DSB_FORCE_DEWAKE once
we are done. For good measure do the same for
DSB_PMCTRL.DSB_ENABLE_DEWAKE.

Experimentally this doens't seem to be actually necessary
(unlike with DSB_FORCE_DEWAKE). That is, the DSB_ENABLE_DEWAKE
doesn't seem to do anything whenever the DSB is not active.
But I'd hate to waste a ton of power in case there I'm wrong
and there is some way DEwake could remaing asserted. One extra
register write is a small price to pay for some peace of mind.

Signed-off-by: Ville Syrjälä 
---
 drivers/gpu/drm/i915/display/intel_dsb.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/i915/display/intel_dsb.c 
b/drivers/gpu/drm/i915/display/intel_dsb.c
index cf710f0bf430..fad37e7856b1 100644
--- a/drivers/gpu/drm/i915/display/intel_dsb.c
+++ b/drivers/gpu/drm/i915/display/intel_dsb.c
@@ -464,8 +464,10 @@ void intel_dsb_finish(struct intel_dsb *dsb)
/*
 * DSB_FORCE_DEWAKE remains active even after DSB is
 * disabled, so make sure to clear it (if set during
-* intel_dsb_commit()).
+* intel_dsb_commit()). And clear DSB_ENABLE_DEWAKE as
+* well for good measure.
 */
+   intel_dsb_reg_write(dsb, DSB_PMCTRL(crtc->pipe, dsb->id), 0);
intel_dsb_reg_write_masked(dsb, DSB_PMCTRL_2(crtc->pipe, dsb->id),
   DSB_FORCE_DEWAKE, 0);
 
-- 
2.44.2