diff mbox series

[v3,1/4] drm/dp: Add helper to set LTTPRs in transparent mode

Message ID 20250103-drm-dp-msm-add-lttpr-transparent-mode-set-v3-1-5c367f4b0763@linaro.org (mailing list archive)
State New
Headers show
Series drm/dp: Rework LTTPR transparent mode handling and add support to msm driver | expand

Commit Message

Abel Vesa Jan. 3, 2025, 12:58 p.m. UTC 
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>
Signed-off-by: Abel Vesa <abel.vesa@linaro.org>
---
 drivers/gpu/drm/display/drm_dp_helper.c | 61 +++++++++++++++++++++++++++++++++
 include/drm/display/drm_dp_helper.h     |  2 ++
 2 files changed, 63 insertions(+)

Comments

Dmitry Baryshkov Jan. 3, 2025, 6:06 p.m. UTC | #1 
On Fri, Jan 03, 2025 at 02:58:15PM +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.
> 
> 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>
> Signed-off-by: Abel Vesa <abel.vesa@linaro.org>
> ---
>  drivers/gpu/drm/display/drm_dp_helper.c | 61 +++++++++++++++++++++++++++++++++
>  include/drm/display/drm_dp_helper.h     |  2 ++
>  2 files changed, 63 insertions(+)
> 

Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
diff mbox series

Patch

diff --git a/drivers/gpu/drm/display/drm_dp_helper.c b/drivers/gpu/drm/display/drm_dp_helper.c
index da3c8521a7fa7d3c9761377363cdd4b44ab1106e..0f665d9adf02cfd16f0c250eb7ae8fe0461f8fdd 100644
--- a/drivers/gpu/drm/display/drm_dp_helper.c
+++ b/drivers/gpu/drm/display/drm_dp_helper.c
@@ -2817,6 +2817,67 @@  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;
+
+	/*
+	 * Roll-back to tranparent mode if setting non-tranparent mode failed
+	 */
+	if (drm_dp_lttpr_set_transparent_mode(aux, false)) {
+		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 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]);