linux-kernel - Re: [PATCH v4 1/4] drm/dp: Add helper to set LTTPRs in transparent mode

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Message-ID: <Z3+9nUwDyyYkB2Jl@linaro.org>
Date: Thu, 9 Jan 2025 14:14:21 +0200
From: Abel Vesa <abel.vesa@...aro.org>
To: Bjorn Andersson <andersson@...nel.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>,
	Dmitry Baryshkov <dmitry.baryshkov@...aro.org>,
	Sean Paul <sean@...rly.run>,
	Marijn Suijten <marijn.suijten@...ainline.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,
	Johan Hovold <johan+linaro@...nel.org>
Subject: Re: [PATCH v4 1/4] drm/dp: Add helper to set LTTPRs in transparent
 mode

On 25-01-08 16:17:47, Bjorn Andersson wrote:
> On Wed, Jan 08, 2025 at 04:31:43PM +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.
> > 
> > Also add a generic wrapper for the helper that handles the explicit
> > disabling of non-transparent mode and its disable->enable sequence
> > mentioned in the DP Standard v2.0 section 3.6.6.1. Do this in order
> > to move this handling out of the vendor specific driver implementation
> > into the generic framework.
> > 
> > Tested-by: Johan Hovold <johan+linaro@...nel.org>
> > Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
> > Reviewed-by: Johan Hovold <johan+linaro@...nel.org>
> > Signed-off-by: Abel Vesa <abel.vesa@...aro.org>
> > ---
> >  drivers/gpu/drm/display/drm_dp_helper.c | 62 +++++++++++++++++++++++++++++++++
> >  include/drm/display/drm_dp_helper.h     |  2 ++
> >  2 files changed, 64 insertions(+)
> > 
> > diff --git a/drivers/gpu/drm/display/drm_dp_helper.c b/drivers/gpu/drm/display/drm_dp_helper.c
> > index da3c8521a7fa7d3c9761377363cdd4b44ab1106e..fa7eff94d408718a1762834597f0cd51376d2596 100644
> > --- a/drivers/gpu/drm/display/drm_dp_helper.c
> > +++ b/drivers/gpu/drm/display/drm_dp_helper.c
> > @@ -2817,6 +2817,68 @@ 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
> 
> kernel-doc functions should have () suffix

Yes, will add.

> 
> > + * @aux: DisplayPort AUX channel
> > + * @enable: Enable or disable transparent mode
> > + *
> > + * Returns 0 on success or a negative error code on failure.
> 
> And this should be "Return: ...".

Will fix as well.

> 
> > + */
> > +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;
> > +	int ret = drm_dp_dpcd_writeb(aux, DP_PHY_REPEATER_MODE, val);
> > +
> > +	if (ret < 0)
> > +		return ret;
> > +
> > +	return (ret == 1) ? 0 : -EIO;
> > +}
> > +EXPORT_SYMBOL(drm_dp_lttpr_set_transparent_mode);
> > +
> > +/**
> > + * drm_dp_lttpr_init - init LTTPR transparency mode according to DP standard
> > + *
> 
> Documentation also explicitly says not to leave a blank line here...

Will drop the blank line.

> 
> Regards,
> Bjorn
> 

Thanks for reviewing!

Abel