linux-kernel - Re: [PATCH v2 4/4] drm/msm/dp: Add support for LTTPR handling

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Message-ID: <Z1moNToiIIB9auSl@hovoldconsulting.com>
Date: Wed, 11 Dec 2024 15:56:53 +0100
From: Johan Hovold <johan@...nel.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>,
	Dmitry Baryshkov <dmitry.baryshkov@...aro.org>,
	Sean Paul <sean@...rly.run>,
	Marijn Suijten <marijn.suijten@...ainline.org>,
	Bjorn Andersson <andersson@...nel.org>,
	Konrad Dybcio <konradybcio@...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 v2 4/4] drm/msm/dp: Add support for LTTPR handling

On Wed, Dec 11, 2024 at 03:04:15PM +0200, Abel Vesa wrote:
 
> +static void msm_dp_display_lttpr_init(struct msm_dp_display_private *dp)
> +{
> +	int lttpr_count;
> +
> +	if (drm_dp_read_lttpr_common_caps(dp->aux, dp->panel->dpcd,
> +					  dp->lttpr_caps))
> +		return;
> +
> +	lttpr_count = drm_dp_lttpr_count(dp->lttpr_caps);

I was gonna say shouldn't you handle errors here, but that explains the
non-negative check I commented on the first patch in the series.

This looks error prone, but I think you should at least update the
kernel doc comment to drm_dp_lttpr_init() in the first patch so that
it's clear that you pass in the number of LTTPRs *or* an errno.

> +
> +	drm_dp_lttpr_init(dp->aux, lttpr_count);
> +}
> +
>  static int msm_dp_display_process_hpd_high(struct msm_dp_display_private *dp)
>  {
>  	struct drm_connector *connector = dp->msm_dp_display.connector;
>  	const struct drm_display_info *info = &connector->display_info;
>  	int rc = 0;
>  
> +	msm_dp_display_lttpr_init(dp);

It looks like you ignore errors on purpose so I guess that's fine.

> +
>  	rc = msm_dp_panel_read_sink_caps(dp->panel, connector);
>  	if (rc)
>  		goto end;

Either way, this is needed for external display on my x1e80100 machines,
while not breaking the X13s:

Tested-by: Johan Hovold <johan+linaro@...nel.org>

Johan