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: <3p3wgzhtptjexplxrluod6sk36xeltpoh4hxg2yagssw7nh7hj@ikc4rssp6zej>
Date: Fri, 3 Jan 2025 20:09:42 +0200
From: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
To: Abel Vesa <abel.vesa@...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 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).

>  	return lttpr_count;
>  
>  out_reset_lttpr_count:
> 
> -- 
> 2.34.1
> 

-- 
With best wishes
Dmitry