thr3ads.net - Nouveau - [PATCH v2 1/4] drm/dp: Add helper to set LTTPRs in transparent mode [Dec 2024]

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Abel Vesa

2024-Dec-11 13:04 UTC

[PATCH v2 1/4] 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.

Signed-off-by: Abel Vesa <abel.vesa at linaro.org>
---
 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

Johan Hovold

2024-Dec-11 14:42 UTC

head link

[PATCH v2 1/4] drm/dp: Add helper to set LTTPRs in transparent mode

On Wed, Dec 11, 2024 at 03:04:12PM +0200, Abel Vesa wrote:
 > +/**
> + * 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;
This looks correct, but I had to go look at drm_dp_dpcd_writeb() to make
sure it never returns 0 (for short transfers).
> +}
> +EXPORT_SYMBOL(drm_dp_lttpr_set_transparent_mode);
This appears to be what the driver currently uses, but why not
EXPORT_SYMBOL_GPL?
> +
> +/**
> + * 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);
Error handling?
> +
> +	if (lttpr_count > 0 && !drm_dp_lttpr_set_transparent_mode(aux,
false))
No need to check lttpr_count again here.
> +		return 0;
I'd check for errors instead of success here and do the rollback before
returning -EINVAL.
> +
> +	/*
> +	 * 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;
And return 0 explicitly here.
> +}
> +EXPORT_SYMBOL(drm_dp_lttpr_init);
In any case this works well and is needed for external display on the
Lenovo ThinkPad T14s, while not breaking the X13s which does not need
it:

Tested-by: Johan Hovold <johan+linaro at kernel.org>

Johan

Dmitry Baryshkov

2024-Dec-11 19:22 UTC

head link

[PATCH v2 1/4] drm/dp: Add helper to set LTTPRs in transparent mode

On Wed, Dec 11, 2024 at 03:04:12PM +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.
> 
> Signed-off-by: Abel Vesa <abel.vesa at linaro.org>
> ---
>  drivers/gpu/drm/display/drm_dp_helper.c | 50
+++++++++++++++++++++++++++++++++
>  include/drm/display/drm_dp_helper.h     |  2 ++
>  2 files changed, 52 insertions(+)
> 
> +/**
> + * 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);
This means that if lttpr_count < 0, then there will be two requests to
set LTTPRs to a transparent mode. Is that expected?
> +
> +	return -EINVAL;
> +}
> +EXPORT_SYMBOL(drm_dp_lttpr_init);
> +
-- 
With best wishes
Dmitry

Nouveau - Dec 2024 - [PATCH v2 1/4] drm/dp: Add helper to set LTTPRs in transparent mode

[PATCH v2 1/4] drm/dp: Add helper to set LTTPRs in transparent mode

[PATCH v2 1/4] drm/dp: Add helper to set LTTPRs in transparent mode

[PATCH v2 1/4] drm/dp: Add helper to set LTTPRs in transparent mode