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

[Jani Nikula]

On Thu, 31 Oct 2024, Imre Deak <imre.deak at 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 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".

But is that a sensible return value?

>
>> + */
>> +

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