linux-kernel - Re: [PATCH RFC 1/4] drm/dp: Add helper to set LTTPRs in transparent mode

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Message-ID: <skyowhfl2qoaaoa4gyj5mf4j3nlznmtc6l5b3oicopmc5u5nxb@f3i2iif3r6ya>
Date: Fri, 1 Nov 2024 22:12:16 +0200
From: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
To: Imre Deak <imre.deak@...el.com>
Cc: Jani Nikula <jani.nikula@...ux.intel.com>, 
	Abel Vesa <abel.vesa@...aro.org>, 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>, 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
Subject: Re: [PATCH RFC 1/4] drm/dp: Add helper to set LTTPRs in transparent
 mode

On Fri, Nov 01, 2024 at 03:43:40PM +0200, Imre Deak wrote:
> On Fri, Nov 01, 2024 at 11:22:13AM +0200, Jani Nikula wrote:
> > On Thu, 31 Oct 2024, Imre Deak <imre.deak@...el.com> wrote:
> > > On Thu, Oct 31, 2024 at 05:12:45PM +0200, Abel Vesa wrote:
> > >> According to the DisplayPort standard, LTTPRs have two operating
> > >> modes:
> > >>  - non-transparent - it replies to DPCD LTTPR field specific AUX
> > >>    requests, while passes through all other AUX requests
> > >>  - transparent - it passes through all AUX requests.
> > >> 
> > >> Switching between this two modes is done by the DPTX by issuing
> > >> an AUX write to the DPCD PHY_REPEATER_MODE register.
> > >> 
> > >> Add a generic helper that allows switching between these modes.
> > >> 
> > >> Signed-off-by: Abel Vesa <abel.vesa@...aro.org>
> > >> ---
> > >>  drivers/gpu/drm/display/drm_dp_helper.c | 17 +++++++++++++++++
> > >>  include/drm/display/drm_dp_helper.h     |  1 +
> > >>  2 files changed, 18 insertions(+)
> > >> 
> > >> diff --git a/drivers/gpu/drm/display/drm_dp_helper.c b/drivers/gpu/drm/display/drm_dp_helper.c
> > >> index 6ee51003de3ce616c3a52653c2f1979ad7658e21..38d612345986ad54b42228902ea718a089d169c4 100644
> > >> --- a/drivers/gpu/drm/display/drm_dp_helper.c
> > >> +++ b/drivers/gpu/drm/display/drm_dp_helper.c
> > >> @@ -2694,6 +2694,23 @@ int drm_dp_lttpr_max_link_rate(const u8 caps[DP_LTTPR_COMMON_CAP_SIZE])
> > >>  }
> > >>  EXPORT_SYMBOL(drm_dp_lttpr_max_link_rate);
> > >>  
> > >> +/**
> > >> + * drm_dp_lttpr_set_transparent_mode - set the LTTPR in transparent mode
> > >> + * @aux: DisplayPort AUX channel
> > >> + * @enable: Enable or disable transparent mode
> > >> + *
> > >> + * Returns 0 on success or a negative error code on failure.
> > >
> > > Should be "Returns 1 on success".
> > 
> > But is that a sensible return value?
> 
> It matches what the function returns, but yes, would make more sense to
> fix the return value instead to be 0 in case of success.

I think returning 0 is better in case of this function.

> 
> > >
> > >> + */
> > >> +
> > 
> > Superfluous newline.
> > 
> > >> +int drm_dp_lttpr_set_transparent_mode(struct drm_dp_aux *aux, bool enable)
> > >> +{
> > >> +	u8 val = enable ? DP_PHY_REPEATER_MODE_TRANSPARENT :
> > >> +			  DP_PHY_REPEATER_MODE_NON_TRANSPARENT;
> > >> +
> > >> +	return drm_dp_dpcd_writeb(aux, DP_PHY_REPEATER_MODE, val);
> > >> +}
> > >> +EXPORT_SYMBOL(drm_dp_lttpr_set_transparent_mode);
> > >> +
> > >>  /**
> > >>   * drm_dp_lttpr_max_lane_count - get the maximum lane count supported by all LTTPRs
> > >>   * @caps: LTTPR common capabilities
> > >> diff --git a/include/drm/display/drm_dp_helper.h b/include/drm/display/drm_dp_helper.h
> > >> index 279624833ea9259809428162f4e845654359f8c9..8821ab2d36b0e04d38ccbdddcb703b34de7ed680 100644
> > >> --- a/include/drm/display/drm_dp_helper.h
> > >> +++ b/include/drm/display/drm_dp_helper.h
> > >> @@ -625,6 +625,7 @@ int drm_dp_read_lttpr_phy_caps(struct drm_dp_aux *aux,
> > >>  			       u8 caps[DP_LTTPR_PHY_CAP_SIZE]);
> > >>  int drm_dp_lttpr_count(const u8 cap[DP_LTTPR_COMMON_CAP_SIZE]);
> > >>  int drm_dp_lttpr_max_link_rate(const u8 caps[DP_LTTPR_COMMON_CAP_SIZE]);
> > >> +int drm_dp_lttpr_set_transparent_mode(struct drm_dp_aux *aux, bool enable);
> > >>  int drm_dp_lttpr_max_lane_count(const u8 caps[DP_LTTPR_COMMON_CAP_SIZE]);
> > >>  bool drm_dp_lttpr_voltage_swing_level_3_supported(const u8 caps[DP_LTTPR_PHY_CAP_SIZE]);
> > >>  bool drm_dp_lttpr_pre_emphasis_level_3_supported(const u8 caps[DP_LTTPR_PHY_CAP_SIZE]);
> > >> 
> > >> -- 
> > >> 2.34.1
> > >> 
> > 
> > -- 
> > Jani Nikula, Intel

-- 
With best wishes
Dmitry