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.
Signed-off-by: Abel Vesa <abel.vesa@xxxxxxxxxx>
---
drivers/gpu/drm/display/drm_dp_helper.c | 50 +++++++++++++++++++++++++++++++++
include/drm/display/drm_dp_helper.h | 2 ++
2 files changed, 52 insertions(+)
diff --git a/drivers/gpu/drm/display/drm_dp_helper.c b/drivers/gpu/drm/display/drm_dp_helper.c
index da3c8521a7fa7d3c9761377363cdd4b44ab1106e..6abc54cd28e93d8101358ce05be51d4516778451 100644
--- a/drivers/gpu/drm/display/drm_dp_helper.c
+++ b/drivers/gpu/drm/display/drm_dp_helper.c
@@ -2817,6 +2817,56 @@ 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.
+ */
+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);
+
+ return ret == 1 ? 0 : ret;
+}
+EXPORT_SYMBOL(drm_dp_lttpr_set_transparent_mode);
+
+/**
+ * drm_dp_lttpr_init - init LTTPR transparency mode according to DP standard
+ *
+ * @aux: DisplayPort AUX channel
+ * @lttpr_count: Number of LTTPRs
+ *
+ * Returns 0 on success or a negative error code on failure.
+ */
+int drm_dp_lttpr_init(struct drm_dp_aux *aux, int lttpr_count)
+{
+ 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.
+ */
+ drm_dp_lttpr_set_transparent_mode(aux, true);
+
+ if (lttpr_count > 0 && !drm_dp_lttpr_set_transparent_mode(aux, false))
+ return 0;
+
+ /*
+ * Roll-back to tranparent mode if setting non-tranparent mode failed or
+ * the number of LTTPRs is invalid
+ */
+ drm_dp_lttpr_set_transparent_mode(aux, true);
+
+ return -EINVAL;
+}
+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
