linux-kernel - Re: [PATCH v3 3/4] drm/i915/dp: Use the generic helper to control LTTPR transparent mode

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Message-ID: <Z3vQfIIDDgnFJsDn@linaro.org>
Date: Mon, 6 Jan 2025 14:45:48 +0200
From: Abel Vesa <abel.vesa@...aro.org>
To: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
Cc: Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
	Maxime Ripard <mripard@...nel.org>,
	Thomas Zimmermann <tzimmermann@...e.de>,
	David Airlie <airlied@...il.com>, Simona Vetter <simona@...ll.ch>,
	Karol Herbst <kherbst@...hat.com>, Lyude Paul <lyude@...hat.com>,
	Danilo Krummrich <dakr@...hat.com>,
	Jani Nikula <jani.nikula@...ux.intel.com>,
	Rodrigo Vivi <rodrigo.vivi@...el.com>,
	Joonas Lahtinen <joonas.lahtinen@...ux.intel.com>,
	Tvrtko Ursulin <tursulin@...ulin.net>,
	Rob Clark <robdclark@...il.com>,
	Abhinav Kumar <quic_abhinavk@...cinc.com>,
	Sean Paul <sean@...rly.run>,
	Marijn Suijten <marijn.suijten@...ainline.org>,
	Bjorn Andersson <andersson@...nel.org>,
	Konrad Dybcio <konradybcio@...nel.org>,
	Johan Hovold <johan@...nel.org>, dri-devel@...ts.freedesktop.org,
	linux-kernel@...r.kernel.org, nouveau@...ts.freedesktop.org,
	intel-gfx@...ts.freedesktop.org, intel-xe@...ts.freedesktop.org,
	linux-arm-msm@...r.kernel.org, freedreno@...ts.freedesktop.org,
	Imre Deak <imre.deak@...el.com>
Subject: Re: [PATCH v3 3/4] drm/i915/dp: Use the generic helper to control
 LTTPR transparent mode

On 25-01-03 20:09:42, Dmitry Baryshkov wrote:
> On Fri, Jan 03, 2025 at 02:58:17PM +0200, Abel Vesa wrote:
> > LTTPRs operating modes are defined by the DisplayPort standard and the
> > generic framework now provides a helper to switch between them, which
> > is handling the explicit disabling of non-transparent mode and its
> > disable->enable sequence mentioned in the DP Standard v2.0 section
> > 3.6.6.1.
> > 
> > So use the new drm generic helper instead as it makes the code a bit
> > cleaner.
> > 
> > Acked-by: Imre Deak <imre.deak@...el.com>
> > Signed-off-by: Abel Vesa <abel.vesa@...aro.org>
> > ---
> >  .../gpu/drm/i915/display/intel_dp_link_training.c  | 24 +++++-----------------
> >  1 file changed, 5 insertions(+), 19 deletions(-)
> > 
> > diff --git a/drivers/gpu/drm/i915/display/intel_dp_link_training.c b/drivers/gpu/drm/i915/display/intel_dp_link_training.c
> > index 8b1977cfec503c70f07af716ee2c00e7605c6adf..c5bad311edf7b9a5cebb633b9e9692bae397f9ed 100644
> > --- a/drivers/gpu/drm/i915/display/intel_dp_link_training.c
> > +++ b/drivers/gpu/drm/i915/display/intel_dp_link_training.c
> > @@ -119,9 +119,6 @@ intel_dp_set_lttpr_transparent_mode(struct intel_dp *intel_dp, bool enable)
> >  	u8 val = enable ? DP_PHY_REPEATER_MODE_TRANSPARENT :
> >  			  DP_PHY_REPEATER_MODE_NON_TRANSPARENT;
> >  
> > -	if (drm_dp_dpcd_write(&intel_dp->aux, DP_PHY_REPEATER_MODE, &val, 1) != 1)
> > -		return false;
> > -
> >  	intel_dp->lttpr_common_caps[DP_PHY_REPEATER_MODE -
> >  				    DP_LT_TUNABLE_PHY_REPEATER_FIELD_DATA_STRUCTURE_REV] = val;
> >  
> > @@ -146,6 +143,7 @@ static bool intel_dp_lttpr_transparent_mode_enabled(struct intel_dp *intel_dp)
> >  static int intel_dp_init_lttpr_phys(struct intel_dp *intel_dp, const u8 dpcd[DP_RECEIVER_CAP_SIZE])
> >  {
> >  	int lttpr_count;
> > +	int ret;
> >  
> >  	if (!intel_dp_read_lttpr_common_caps(intel_dp, dpcd))
> >  		return 0;
> > @@ -172,22 +170,8 @@ static int intel_dp_init_lttpr_phys(struct intel_dp *intel_dp, const u8 dpcd[DP_
> >  		return lttpr_count;
> >  	}
> >  
> > -	/*
> > -	 * See DP Standard v2.0 3.6.6.1. about the explicit disabling of
> > -	 * non-transparent mode and the disable->enable non-transparent mode
> > -	 * sequence.
> > -	 */
> > -	intel_dp_set_lttpr_transparent_mode(intel_dp, true);
> > -
> > -	/*
> > -	 * In case of unsupported number of LTTPRs or failing to switch to
> > -	 * non-transparent mode fall-back to transparent link training mode,
> > -	 * still taking into account any LTTPR common lane- rate/count limits.
> > -	 */
> > -	if (lttpr_count < 0)
> > -		goto out_reset_lttpr_count;
> > -
> > -	if (!intel_dp_set_lttpr_transparent_mode(intel_dp, false)) {
> > +	ret = drm_dp_lttpr_init(&intel_dp->aux, lttpr_count);
> > +	if (ret) {
> >  		lt_dbg(intel_dp, DP_PHY_DPRX,
> >  		       "Switching to LTTPR non-transparent LT mode failed, fall-back to transparent mode\n");
> >  
> > @@ -196,6 +180,8 @@ static int intel_dp_init_lttpr_phys(struct intel_dp *intel_dp, const u8 dpcd[DP_
> >  		goto out_reset_lttpr_count;
> >  	}
> >  
> > +	intel_dp_set_lttpr_transparent_mode(intel_dp, false);
> > +
> 
> I think the code now misses a way to update intel_dp->lttpr_common_caps
> in a transparent-mode case:
> intel_dp_set_lttpr_transparent_mode(intel_dp, true).

It is being called if the drm_dp_lttpr_init() returns a non-zero value,
but that is not part of the diff here.

> 
> >  	return lttpr_count;
> >  
> >  out_reset_lttpr_count:
> > 
> > -- 
> > 2.34.1
> > 
> 
> -- 
> With best wishes
> Dmitry