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

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives
Hash Suite: Windows password security audit tool. GUI, reports in PDF.
[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Message-ID: <b4z2o4sgyjyh7wqbybtifi5evhh7b3tgfujson6l5ajmjdwt3f@x2xz6iod54vz>
Date: Wed, 8 Jan 2025 16:17:47 -0600
From: Bjorn Andersson <andersson@...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>, 
	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 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

> + * @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: ...".

> + */
> +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...

Regards,
Bjorn

> + * @aux: DisplayPort AUX channel
> + * @lttpr_count: Number of LTTPRs. Between 0 and 8, according to DP standard.
> + *               Negative error code for any non-valid number.
> + *               See drm_dp_lttpr_count().
> + *
> + * Returns 0 on success or a negative error code on failure.
> + */
> +int drm_dp_lttpr_init(struct drm_dp_aux *aux, int lttpr_count)
> +{
> +	int ret;
> +
> +	if (!lttpr_count)
> +		return 0;
> +
> +	/*
> +	 * 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.
> +	 */
> +	ret = drm_dp_lttpr_set_transparent_mode(aux, true);
> +	if (ret)
> +		return ret;
> +
> +	if (lttpr_count < 0)
> +		return -ENODEV;
> +
> +	if (drm_dp_lttpr_set_transparent_mode(aux, false)) {
> +		/*
> +		 * Roll-back to transparent mode if setting non-transparent
> +		 * mode has failed
> +		 */
> +		drm_dp_lttpr_set_transparent_mode(aux, true);
> +		return -EINVAL;
> +	}
> +
> +	return 0;
> +}
> +EXPORT_SYMBOL(drm_dp_lttpr_init);
> +
>  /**
>   * 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 8f4054a560396a43750570a8c2e95624039ab8ad..3311df3b58255cf0620391d0948ccf6b569a8a34 100644
> --- a/include/drm/display/drm_dp_helper.h
> +++ b/include/drm/display/drm_dp_helper.h
> @@ -630,6 +630,8 @@ 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_init(struct drm_dp_aux *aux, int lttpr_count);
>  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
>