From 5e7715478c273e5b17b08942182bc0350b7ef3a6 Mon Sep 17 00:00:00 2001
From: Abel Vesa <abel.vesa@linaro.org>
Date: Mon, 3 Feb 2025 12:57:56 +0200
Subject: [PATCH] drm/dp: Add helper to set LTTPRs in transparent mode
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@kernel.org>
Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Reviewed-by: Johan Hovold <johan+linaro@kernel.org>
Reviewed-by: Abhinav Kumar <quic_abhinavk@quicinc.com>
Signed-off-by: Abel Vesa <abel.vesa@linaro.org>
Acked-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20250203-drm-dp-msm-add-lttpr-transparent-mode-set-v5-1-c865d0e56d6e@linaro.org
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
---
drivers/gpu/drm/display/drm_dp_helper.c | 61 +++++++++++++++++++++++++
include/drm/display/drm_dp_helper.h | 2 +
2 files changed, 63 insertions(+)
diff --git a/drivers/gpu/drm/display/drm_dp_helper.c b/drivers/gpu/drm/display/drm_dp_helper.c
index f5c596234729d..dbce1c3f49691 100644
--- a/drivers/gpu/drm/display/drm_dp_helper.c
+++ b/drivers/gpu/drm/display/drm_dp_helper.c
@@ -2875,6 +2875,67 @@ 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);
+
+ 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
+ * @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 89a34dff85a4e..5ae4241959f24 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]);
--
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