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

[Imre Deak <imre.deak@intel.com>]

On Fri, Nov 01, 2024 at 11:22:13AM +0200, Jani Nikula wrote:
> On Thu, 31 Oct 2024, Imre Deak <imre.deak@intel.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@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".
> 
> 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.

> >
> >> + */
> >> +
> 
> 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