Re: [PATCH v4 10/13] drm/i915/psr: Remove DSB_SKIP_WAITS_EN chicken bit

["Ville Syrjälä" <ville.syrjala@linux.intel.com>]

On Fri, Jan 24, 2025 at 12:56:21PM +0200, Jouni Högander wrote:
> We have different approach on how flip is considered being complete. We are
> waiting for vblank on DSB and generate interrupt when it happens and this
> interrupt is considered as indication of completion -> we definitely do not
> want to skip vblank wait.
> 
> Also not skipping scanline wait shouldn't cause any problems if we are in
> DEEP_SLEEP PIPEDSL register is returning 0 -> evasion does nothing and if
> we are not in DEEP_SLEEP evasion works same way as without PSR.
> 
> Signed-off-by: Jouni Högander <jouni.hogander@intel.com>
> ---
>  drivers/gpu/drm/i915/display/intel_dsb.c | 5 ++---
>  1 file changed, 2 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/display/intel_dsb.c b/drivers/gpu/drm/i915/display/intel_dsb.c
> index 89d3496bcbdbd..bb77ded8bf726 100644
> --- a/drivers/gpu/drm/i915/display/intel_dsb.c
> +++ b/drivers/gpu/drm/i915/display/intel_dsb.c
> @@ -168,13 +168,12 @@ static u32 dsb_chicken(struct intel_atomic_state *state,
>  		       struct intel_crtc *crtc)
>  {

IIRC bspec suggests that we should always set DSB_SKIP_WAITS_EN,
so we should probably have a comment here explaining our reason
for omitting it. Otherwise I fear that someone is going to be
blindly reading the spec and then try to add the bit back.

>  	if (pre_commit_is_vrr_active(state, crtc))
> -		return DSB_SKIP_WAITS_EN |
> -			DSB_CTRL_WAIT_SAFE_WINDOW |
> +		return DSB_CTRL_WAIT_SAFE_WINDOW |
>  			DSB_CTRL_NO_WAIT_VBLANK |
>  			DSB_INST_WAIT_SAFE_WINDOW |
>  			DSB_INST_NO_WAIT_VBLANK;
>  	else
> -		return DSB_SKIP_WAITS_EN;
> +		return 0;
>  }
>  
>  static bool assert_dsb_has_room(struct intel_dsb *dsb)
> -- 
> 2.43.0

-- 
Ville Syrjälä
Intel