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

[Imre Deak]

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 at linaro.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".

> + */
> +
> +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
>