[Intel-gfx] [PATCH v4] drm/i915/display: Support PSR entry VSC packet to be transmitted one frame earlier

[Kahola, Mika]

> -----Original Message-----
> From: Jani Nikula <jani.nikula at linux.intel.com>
> Sent: Wednesday, November 8, 2023 7:42 PM
> To: Ville Syrjälä <ville.syrjala at linux.intel.com>; Kahola, Mika <mika.kahola at intel.com>
> Cc: intel-gfx at lists.freedesktop.org
> Subject: Re: [Intel-gfx] [PATCH v4] drm/i915/display: Support PSR entry VSC packet to be transmitted one frame earlier
> 
> On Wed, 08 Nov 2023, Ville Syrjälä <ville.syrjala at linux.intel.com> wrote:
> > On Wed, Nov 08, 2023 at 06:59:18PM +0200, Ville Syrjälä wrote:
> >> On Mon, Nov 06, 2023 at 01:42:28PM +0200, Mika Kahola wrote:
> >> > Display driver shall read DPCD 00071h[3:1] during configuration to
> >> > get PSR setup time. This register provides the setup time
> >> > requirement on the VSC SDP entry packet. If setup time cannot be
> >> > met with the current timings (e.g., PSR setup time + other blanking
> >> > requirements > blanking time), driver should enable sending VSC SDP
> >> > one frame earlier before sending the capture frame.
> >> >
> >> > BSpec: 69895 (PSR Entry Setup Frames 17:16)
> >> >
> >> > v2: Write frames before su entry to correct register (Ville, Jouni)
> >> >     Move frames before su entry calculation to it's
> >> >     own function (Ville, Jouni)
> >> >     Rename PSR Entry Setup Frames register to indicate
> >> >     Lunarlake specificity (Jouni)
> >> > v3: Modify setup entry frames calculation function to
> >> >     return the actual frames (Ville)
> >> >     Match comment with actual implementation (Jouni)
> >> > v4: Drop "set" from function naming (Jouni, Ville)
> >> >     Use i915 instead of dev_priv (Jouni)
> >> >
> >> > Signed-off-by: Mika Kahola <mika.kahola at intel.com>
> >> > ---
> >> >  .../drm/i915/display/intel_display_types.h    |  1 +
> >> >  drivers/gpu/drm/i915/display/intel_psr.c      | 82 +++++++++++++++----
> >> >  drivers/gpu/drm/i915/display/intel_psr_regs.h |  2 +
> >> >  3 files changed, 71 insertions(+), 14 deletions(-)
> >> >
> >> > diff --git a/drivers/gpu/drm/i915/display/intel_display_types.h
> >> > b/drivers/gpu/drm/i915/display/intel_display_types.h
> >> > index 047fe3f8905a..92f06d67fd1e 100644
> >> > --- a/drivers/gpu/drm/i915/display/intel_display_types.h
> >> > +++ b/drivers/gpu/drm/i915/display/intel_display_types.h
> >> > @@ -1708,6 +1708,7 @@ struct intel_psr {
> >> >  	u32 dc3co_exitline;
> >> >  	u32 dc3co_exit_delay;
> >> >  	struct delayed_work dc3co_work;
> >> > +	u8 entry_setup_frames;
> >> >  };
> >> >
> >> >  struct intel_dp {
> >> > diff --git a/drivers/gpu/drm/i915/display/intel_psr.c
> >> > b/drivers/gpu/drm/i915/display/intel_psr.c
> >> > index 920f77336163..fc242916349b 100644
> >> > --- a/drivers/gpu/drm/i915/display/intel_psr.c
> >> > +++ b/drivers/gpu/drm/i915/display/intel_psr.c
> >> > @@ -593,6 +593,9 @@ static void intel_psr_enable_sink(struct intel_dp *intel_dp)
> >> >  	if (intel_dp->psr.req_psr2_sdp_prior_scanline)
> >> >  		dpcd_val |= DP_PSR_SU_REGION_SCANLINE_CAPTURE;
> >> >
> >> > +	if (intel_dp->psr.entry_setup_frames > 0)
> >> > +		dpcd_val |= DP_PSR_FRAME_CAPTURE;
> >> > +
> >> >  	drm_dp_dpcd_writeb(&intel_dp->aux, DP_PSR_EN_CFG, dpcd_val);
> >> >
> >> >  	drm_dp_dpcd_writeb(&intel_dp->aux, DP_SET_POWER,
> >> > DP_SET_POWER_D0); @@ -691,6 +694,9 @@ static void hsw_activate_psr1(struct intel_dp *intel_dp)
> >> >  	if (DISPLAY_VER(dev_priv) >= 8)
> >> >  		val |= EDP_PSR_CRC_ENABLE;
> >> >
> >> > +	if (DISPLAY_VER(dev_priv) >= 20)
> >> > +		val |=
> >> > +LNL_EDP_PSR_ENTRY_SETUP_FRAMES(intel_dp->psr.entry_setup_frames);
> >> > +
> >> >  	intel_de_rmw(dev_priv, psr_ctl_reg(dev_priv, cpu_transcoder),
> >> >  		     ~EDP_PSR_RESTORE_PSR_ACTIVE_CTX_MASK, val);  } @@ -728,11
> >> > +734,27 @@ static int psr2_block_count(struct intel_dp *intel_dp)
> >> >  	return psr2_block_count_lines(intel_dp) / 4;  }
> >> >
> >> > +static u8 frames_before_su_entry(struct intel_dp *intel_dp)
> >>           ^^
> >>
> >> That vs -ETIME broke my tgl.
> >>
> >> > +static u8 intel_psr_entry_setup_frames(struct intel_dp *intel_dp,
> >             ^^
> > No, actually that ...
> 
> *sigh*
> 
> I eyeballed the patch and the u8 and thought about giving my standard issue "please use ints unless you have specific reasons to
> use something else" comment. But didn't.

So it's time to switch to use ints. Thought entry_setup_frames would fit to u8 but I guess wasn't the case after all.

Thanks for spotting this!

-Mika- 
> 
> It's a "code smell". It's suspicious even if it isn't broken.
> 
> BR,
> Jani.
> 
> 
> >
> >> > +					   const struct drm_display_mode *adjusted_mode) {
> >> > +	struct drm_i915_private *i915 = dp_to_i915(intel_dp);
> >> > +	int psr_setup_time = drm_dp_psr_setup_time(intel_dp->psr_dpcd);
> >> > +	u8 entry_setup_frames = 0;
> >         ^^
> > ... and that.
> 
> --
> Jani Nikula, Intel