[PATCH v6 1/1] drm/mediatek: Adjust bandwidth limit for DP

[PATCH v6 1/1] drm/mediatek: Adjust bandwidth limit for DP

[Liankun Yang]

By adjusting the order of link training and relocating it to HPD,
link training can identify the usability of each lane in the current link.

It also supports handling signal instability and weakness due to
environmental issues, enabling the acquisition of a stable bandwidth
for the current link. Subsequently, DP work can proceed based on
the actual maximum bandwidth.

It should training in the hpd event thread.
Check the mode with lane count and link rate of training.

If we're eDP and capabilities were already parsed we can skip
reading again because eDP panels aren't hotpluggable hence the
caps and training information won't ever change in a boot life

Therefore, bridge typec judgment is required for edp training in
atomic_enable function.

Signed-off-by: Liankun Yang <liankun.yang@mediatek.com>
---
Change in V6:
- Fixed power on in atomic enable.
- Fixed parse capability for edp.
Per suggestion from the previous thread:
https://patchwork.kernel.org/project/linux-mediatek/patch/20250630080824.7107-1-liankun.yang@mediatek.com/

Change in V5:
- Fixed the issue that the 4th version of the patch caused DP to have no screen.
Per suggestion from the previous thread:
https://patchwork.kernel.org/project/linux-mediatek/patch/20250625095446.31726-1-liankun.yang@mediatek.com/

Change in V4:
- Tested the internal eDP display on MT8195 Tomato and it is fine.
Per suggestion from the previous thread:
https://patchwork.kernel.org/project/linux-mediatek/patch/20250318140236.13650-2-liankun.yang@mediatek.com/

Change in V3:
- Remove 'mtk_dp->enabled = false" in atomic disable.
- Remove 'mtk_dp->enabled = true" in atomic enable.
Per suggestion from the previous thread:
https://patchwork.kernel.org/project/linux-mediatek/patch/20241025083036.8829-4-liankun.yang@mediatek.com/

Change in V2:
- Adjust DP training timing.
- Adjust parse capabilities timing.
- Add power on/off for connect/disconnect.
Per suggestion from the previous thread:
https://patchwork.kernel.org/project/linux-mediatek/patch/20240315015233.2023-1-liankun.yang@mediatek.com/
---
 drivers/gpu/drm/mediatek/mtk_dp.c | 41 ++++++++++++++++++++++++-------
 1 file changed, 32 insertions(+), 9 deletions(-)

diff --git a/drivers/gpu/drm/mediatek/mtk_dp.c b/drivers/gpu/drm/mediatek/mtk_dp.c
index bef6eeb30d3e..384496e49118 100644
--- a/drivers/gpu/drm/mediatek/mtk_dp.c
+++ b/drivers/gpu/drm/mediatek/mtk_dp.c
@@ -1976,6 +1976,7 @@ static irqreturn_t mtk_dp_hpd_event_thread(int hpd, void *dev)
 	struct mtk_dp *mtk_dp = dev;
 	unsigned long flags;
 	u32 status;
+	int ret;
 
 	if (mtk_dp->need_debounce && mtk_dp->train_info.cable_plugged_in)
 		msleep(100);
@@ -1994,9 +1995,28 @@ static irqreturn_t mtk_dp_hpd_event_thread(int hpd, void *dev)
 			memset(&mtk_dp->info.audio_cur_cfg, 0,
 			       sizeof(mtk_dp->info.audio_cur_cfg));
 
+			mtk_dp->enabled = false;
+			/* power off aux */
+			mtk_dp_update_bits(mtk_dp, MTK_DP_TOP_PWR_STATE,
+					   DP_PWR_STATE_BANDGAP_TPLL,
+					   DP_PWR_STATE_MASK);
+
 			mtk_dp->need_debounce = false;
 			mod_timer(&mtk_dp->debounce_timer,
 				  jiffies + msecs_to_jiffies(100) - 1);
+		} else {
+			mtk_dp_aux_panel_poweron(mtk_dp, true);
+
+			ret = mtk_dp_parse_capabilities(mtk_dp);
+			if (ret)
+				drm_err(mtk_dp->drm_dev, "Can't parse capabilities\n");
+
+			/* Training */
+			ret = mtk_dp_training(mtk_dp);
+			if (ret)
+				drm_err(mtk_dp->drm_dev, "Training failed, %d\n", ret);
+
+			mtk_dp->enabled = true;
 		}
 	}
 
@@ -2167,7 +2187,8 @@ static const struct drm_edid *mtk_dp_edid_read(struct drm_bridge *bridge,
 	 * Parse capability here to let atomic_get_input_bus_fmts and
 	 * mode_valid use the capability to calculate sink bitrates.
 	 */
-	if (mtk_dp_parse_capabilities(mtk_dp)) {
+	if (mtk_dp->bridge.type == DRM_MODE_CONNECTOR_eDP &&
+	    mtk_dp_parse_capabilities(mtk_dp)) {
 		drm_err(mtk_dp->drm_dev, "Can't parse capabilities\n");
 		drm_edid_free(drm_edid);
 		drm_edid = NULL;
@@ -2355,6 +2376,7 @@ static void mtk_dp_bridge_atomic_enable(struct drm_bridge *bridge,
 					struct drm_atomic_state *state)
 {
 	struct mtk_dp *mtk_dp = mtk_dp_from_bridge(bridge);
+	bool enabled = mtk_dp->enabled;
 	int ret;
 
 	mtk_dp->conn = drm_atomic_get_new_connector_for_encoder(state,
@@ -2365,13 +2387,16 @@ static void mtk_dp_bridge_atomic_enable(struct drm_bridge *bridge,
 		return;
 	}
 
-	mtk_dp_aux_panel_poweron(mtk_dp, true);
+	if (!enabled)
+		mtk_dp_aux_panel_poweron(mtk_dp, true);
 
-	/* Training */
-	ret = mtk_dp_training(mtk_dp);
-	if (ret) {
-		drm_err(mtk_dp->drm_dev, "Training failed, %d\n", ret);
-		goto power_off_aux;
+	if (mtk_dp->data->bridge_type == DRM_MODE_CONNECTOR_eDP) {
+		/* Training */
+		ret = mtk_dp_training(mtk_dp);
+		if (ret) {
+			drm_err(mtk_dp->drm_dev, "Training failed, %d\n", ret);
+			goto power_off_aux;
+		}
 	}
 
 	ret = mtk_dp_video_config(mtk_dp);
@@ -2391,7 +2416,6 @@ static void mtk_dp_bridge_atomic_enable(struct drm_bridge *bridge,
 		       sizeof(mtk_dp->info.audio_cur_cfg));
 	}
 
-	mtk_dp->enabled = true;
 	mtk_dp_update_plugged_status(mtk_dp);
 
 	return;
@@ -2406,7 +2430,6 @@ static void mtk_dp_bridge_atomic_disable(struct drm_bridge *bridge,
 {
 	struct mtk_dp *mtk_dp = mtk_dp_from_bridge(bridge);
 
-	mtk_dp->enabled = false;
 	mtk_dp_update_plugged_status(mtk_dp);
 	mtk_dp_video_enable(mtk_dp, false);
 	mtk_dp_audio_mute(mtk_dp, true);
-- 
2.45.2

Re: [PATCH v6 1/1] drm/mediatek: Adjust bandwidth limit for DP

[CK Hu (胡俊光)]

On Fri, 2025-08-22 at 20:04 +0800, Liankun Yang wrote:
> By adjusting the order of link training and relocating it to HPD,
> link training can identify the usability of each lane in the current link.
> 
> It also supports handling signal instability and weakness due to
> environmental issues, enabling the acquisition of a stable bandwidth
> for the current link. Subsequently, DP work can proceed based on
> the actual maximum bandwidth.
> 
> It should training in the hpd event thread.
> Check the mode with lane count and link rate of training.
> 
> If we're eDP and capabilities were already parsed we can skip
> reading again because eDP panels aren't hotpluggable hence the
> caps and training information won't ever change in a boot life
> 
> Therefore, bridge typec judgment is required for edp training in
> atomic_enable function.
> 
> Signed-off-by: Liankun Yang <liankun.yang@mediatek.com>
> ---
> Change in V6:
> - Fixed power on in atomic enable.
> - Fixed parse capability for edp.
> Per suggestion from the previous thread:
> https://urldefense.com/v3/__https://patchwork.kernel.org/project/linux-mediatek/patch/20250630080824.7107-1-liankun.yang@mediatek.com/__;!!CTRNKA9wMg0ARbw!kSLrY_ehXtIJ21a_ljnX7EmDtD92n8RfjW9Jee6qRfKzC8ekpkvvRcMoJRIo03WgQAm_L7R3zKrr5kS1FUKM6ag$ 
> 
> Change in V5:
> - Fixed the issue that the 4th version of the patch caused DP to have no screen.
> Per suggestion from the previous thread:
> https://urldefense.com/v3/__https://patchwork.kernel.org/project/linux-mediatek/patch/20250625095446.31726-1-liankun.yang@mediatek.com/__;!!CTRNKA9wMg0ARbw!kSLrY_ehXtIJ21a_ljnX7EmDtD92n8RfjW9Jee6qRfKzC8ekpkvvRcMoJRIo03WgQAm_L7R3zKrr5kS1Nx-fs5M$ 
> 
> Change in V4:
> - Tested the internal eDP display on MT8195 Tomato and it is fine.
> Per suggestion from the previous thread:
> https://urldefense.com/v3/__https://patchwork.kernel.org/project/linux-mediatek/patch/20250318140236.13650-2-liankun.yang@mediatek.com/__;!!CTRNKA9wMg0ARbw!kSLrY_ehXtIJ21a_ljnX7EmDtD92n8RfjW9Jee6qRfKzC8ekpkvvRcMoJRIo03WgQAm_L7R3zKrr5kS1osP1SG0$ 
> 
> Change in V3:
> - Remove 'mtk_dp->enabled = false" in atomic disable.
> - Remove 'mtk_dp->enabled = true" in atomic enable.
> Per suggestion from the previous thread:
> https://urldefense.com/v3/__https://patchwork.kernel.org/project/linux-mediatek/patch/20241025083036.8829-4-liankun.yang@mediatek.com/__;!!CTRNKA9wMg0ARbw!kSLrY_ehXtIJ21a_ljnX7EmDtD92n8RfjW9Jee6qRfKzC8ekpkvvRcMoJRIo03WgQAm_L7R3zKrr5kS1MjQ5GiU$ 
> 
> Change in V2:
> - Adjust DP training timing.
> - Adjust parse capabilities timing.
> - Add power on/off for connect/disconnect.
> Per suggestion from the previous thread:
> https://urldefense.com/v3/__https://patchwork.kernel.org/project/linux-mediatek/patch/20240315015233.2023-1-liankun.yang@mediatek.com/__;!!CTRNKA9wMg0ARbw!kSLrY_ehXtIJ21a_ljnX7EmDtD92n8RfjW9Jee6qRfKzC8ekpkvvRcMoJRIo03WgQAm_L7R3zKrr5kS1iJHpMzY$ 
> ---
>  drivers/gpu/drm/mediatek/mtk_dp.c | 41 ++++++++++++++++++++++++-------
>  1 file changed, 32 insertions(+), 9 deletions(-)
> 
> diff --git a/drivers/gpu/drm/mediatek/mtk_dp.c b/drivers/gpu/drm/mediatek/mtk_dp.c
> index bef6eeb30d3e..384496e49118 100644
> --- a/drivers/gpu/drm/mediatek/mtk_dp.c
> +++ b/drivers/gpu/drm/mediatek/mtk_dp.c
> @@ -1976,6 +1976,7 @@ static irqreturn_t mtk_dp_hpd_event_thread(int hpd, void *dev)
>  	struct mtk_dp *mtk_dp = dev;
>  	unsigned long flags;
>  	u32 status;
> +	int ret;
>  
>  	if (mtk_dp->need_debounce && mtk_dp->train_info.cable_plugged_in)
>  		msleep(100);
> @@ -1994,9 +1995,28 @@ static irqreturn_t mtk_dp_hpd_event_thread(int hpd, void *dev)
>  			memset(&mtk_dp->info.audio_cur_cfg, 0,
>  			       sizeof(mtk_dp->info.audio_cur_cfg));
>  
> +			mtk_dp->enabled = false;

I'm not sure eDP would have hot-plug event or not.
If eDP also has hot-plug event (once), add do this only for DP

if (mtk_dp->data->bridge_type != DRM_MODE_CONNECTOR_eDP) {
	/* Action only for DP */
}

> +			/* power off aux */
> +			mtk_dp_update_bits(mtk_dp, MTK_DP_TOP_PWR_STATE,
> +					   DP_PWR_STATE_BANDGAP_TPLL,
> +					   DP_PWR_STATE_MASK);

Why not use mtk_dp_aux_panel_poweron(mtk_dp, false)?
When plug in, you call mtk_dp_aux_panel_poweron(mtk_dp, true),
I would like it to be symmetric.
If not symmetric, add comment to describe why it's not symmetric.

> +
>  			mtk_dp->need_debounce = false;
>  			mod_timer(&mtk_dp->debounce_timer,
>  				  jiffies + msecs_to_jiffies(100) - 1);
> +		} else {
> +			mtk_dp_aux_panel_poweron(mtk_dp, true);
> +
> +			ret = mtk_dp_parse_capabilities(mtk_dp);
> +			if (ret)
> +				drm_err(mtk_dp->drm_dev, "Can't parse capabilities\n");
> +
> +			/* Training */
> +			ret = mtk_dp_training(mtk_dp);
> +			if (ret)
> +				drm_err(mtk_dp->drm_dev, "Training failed, %d\n", ret);
> +
> +			mtk_dp->enabled = true;
>  		}
>  	}
>  
> @@ -2167,7 +2187,8 @@ static const struct drm_edid *mtk_dp_edid_read(struct drm_bridge *bridge,
>  	 * Parse capability here to let atomic_get_input_bus_fmts and
>  	 * mode_valid use the capability to calculate sink bitrates.
>  	 */
> -	if (mtk_dp_parse_capabilities(mtk_dp)) {
> +	if (mtk_dp->bridge.type == DRM_MODE_CONNECTOR_eDP &&
> +	    mtk_dp_parse_capabilities(mtk_dp)) {

I think this modification is related to what you say:

"If we're eDP and capabilities were already parsed we can skip
reading again because eDP panels aren't hotpluggable hence the
caps and training information won't ever change in a boot life"

I think this modification is not related to the title.
This is to improve eDP function not DP.
So separate this to another patch.

>  		drm_err(mtk_dp->drm_dev, "Can't parse capabilities\n");
>  		drm_edid_free(drm_edid);
>  		drm_edid = NULL;
> @@ -2355,6 +2376,7 @@ static void mtk_dp_bridge_atomic_enable(struct drm_bridge *bridge,
>  					struct drm_atomic_state *state)
>  {
>  	struct mtk_dp *mtk_dp = mtk_dp_from_bridge(bridge);
> +	bool enabled = mtk_dp->enabled;
>  	int ret;
>  
>  	mtk_dp->conn = drm_atomic_get_new_connector_for_encoder(state,
> @@ -2365,13 +2387,16 @@ static void mtk_dp_bridge_atomic_enable(struct drm_bridge *bridge,
>  		return;
>  	}
>  
> -	mtk_dp_aux_panel_poweron(mtk_dp, true);
> +	if (!enabled)
> +		mtk_dp_aux_panel_poweron(mtk_dp, true);
>  
> -	/* Training */
> -	ret = mtk_dp_training(mtk_dp);
> -	if (ret) {
> -		drm_err(mtk_dp->drm_dev, "Training failed, %d\n", ret);
> -		goto power_off_aux;
> +	if (mtk_dp->data->bridge_type == DRM_MODE_CONNECTOR_eDP) {
> +		/* Training */
> +		ret = mtk_dp_training(mtk_dp);
> +		if (ret) {
> +			drm_err(mtk_dp->drm_dev, "Training failed, %d\n", ret);
> +			goto power_off_aux;
> +		}
>  	}

if (mtk_dp->data->bridge_type == DRM_MODE_CONNECTOR_eDP) {
	mtk_dp_aux_panel_poweron(mtk_dp, true);

	/* Training */
	ret = mtk_dp_training(mtk_dp);
	if (ret) {
		drm_err(mtk_dp->drm_dev, "Training failed, %d\n", ret);
		goto power_off_aux;
	}
}

>  
>  	ret = mtk_dp_video_config(mtk_dp);
> @@ -2391,7 +2416,6 @@ static void mtk_dp_bridge_atomic_enable(struct drm_bridge *bridge,
>  		       sizeof(mtk_dp->info.audio_cur_cfg));
>  	}
>  
> -	mtk_dp->enabled = true;

if (mtk_dp->data->bridge_type == DRM_MODE_CONNECTOR_eDP)
	mtk_dp->enabled = true;

>  	mtk_dp_update_plugged_status(mtk_dp);
>  
>  	return;
> @@ -2406,7 +2430,6 @@ static void mtk_dp_bridge_atomic_disable(struct drm_bridge *bridge,
>  {
>  	struct mtk_dp *mtk_dp = mtk_dp_from_bridge(bridge);
>  
> -	mtk_dp->enabled = false;

if (mtk_dp->data->bridge_type == DRM_MODE_CONNECTOR_eDP)
	mtk_dp->enabled = false;

Regards,
CK

>  	mtk_dp_update_plugged_status(mtk_dp);
>  	mtk_dp_video_enable(mtk_dp, false);
>  	mtk_dp_audio_mute(mtk_dp, true);