linux-kernel - Re: [PATCH v4 drm-dp 02/11] drm/hisilicon/hibmc: fix dp probabilistical detect errors after HPD irq

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Message-ID: <b859e000-5809-414e-acb4-7fcf222e4554@huawei.com>
Date: Mon, 18 Aug 2025 15:42:24 +0800
From: Yongbang Shi <shiyongbang@...wei.com>
To: Dmitry Baryshkov <dmitry.baryshkov@....qualcomm.com>
CC: <xinliang.liu@...aro.org>, <tiantao6@...ilicon.com>,
	<maarten.lankhorst@...ux.intel.com>, <mripard@...nel.org>,
	<tzimmermann@...e.de>, <airlied@...il.com>, <daniel@...ll.ch>,
	<kong.kongxinwei@...ilicon.com>, <liangjian010@...wei.com>,
	<chenjianmin@...wei.com>, <fengsheng5@...wei.com>, <libaihan@...wei.com>,
	<shenjian15@...wei.com>, <shaojijie@...wei.com>,
	<dri-devel@...ts.freedesktop.org>, <linux-kernel@...r.kernel.org>,
	<shiyongbang@...wei.com>
Subject: Re: [PATCH v4 drm-dp 02/11] drm/hisilicon/hibmc: fix dp
 probabilistical detect errors after HPD irq

> On Thu, Aug 14, 2025 at 08:19:41PM +0800, Yongbang Shi wrote:
>>> On Wed, Aug 13, 2025 at 05:42:29PM +0800, Yongbang Shi wrote:
>>>> From: Baihan Li <libaihan@...wei.com>
>>>>
>>>> The debouncing when HPD pulled out still remains sometimes, 200ms still can
>>>> not ensure helper_detect() is correct. So add a flag to hold the sink
>>>> status, and changed detect_ctx() functions by using flag to check status.
>>> THis doesn't explain what is wrong with
>>> drm_connector_helper_detect_from_ddc(). In the end, this function
>>> doesn't use the HPD pin.
>> I'm sorry about the misunderstanding.
>> The issue is that after plugging or unplugging the monitor, the driver takes no action sometimes
>> even though an interrupt is triggered. The root cause is that drm_connector_helper_detect_from_ddc()
>> still returns connected status when the monitor is unplugged.
>> And I will fix the way in the end.
> Can you perform a normal DP detection: read DPCD and check that there is
> a DPRX attached and that it's either non-branch device or it has one or
> more sinks?

Alright! I will add read_dpcd_caps() and read_sink_count_cap() here to detect DP.

Thanks for your tips!


>> Thanks,
>> Baihan Li!
>>
>>
>>>> Fixes: 3c7623fb5bb6 ("drm/hisilicon/hibmc: Enable this hot plug detect of irq feature")
>>>> Signed-off-by: Baihan Li <libaihan@...wei.com>
>>>> Signed-off-by: Yongbang Shi <shiyongbang@...wei.com>
>>>> ---
>>>> ChangeLog:
>>>> v3 -> v4:
>>>>     - remove link training process in hibmc_dp_detect(), suggested by Dmitry Baryshkov.
>>>>     - remove if (dev->registered), suggested by Dmitry Baryshkov.
>>>> ---
>>>>    drivers/gpu/drm/hisilicon/hibmc/dp/dp_hw.h    |  1 +
>>>>    .../gpu/drm/hisilicon/hibmc/hibmc_drm_dp.c    | 19 ++++++++++++-------
>>>>    2 files changed, 13 insertions(+), 7 deletions(-)
>>>>
>>>> diff --git a/drivers/gpu/drm/hisilicon/hibmc/dp/dp_hw.h b/drivers/gpu/drm/hisilicon/hibmc/dp/dp_hw.h
>>>> index 665f5b166dfb..68867475508c 100644
>>>> --- a/drivers/gpu/drm/hisilicon/hibmc/dp/dp_hw.h
>>>> +++ b/drivers/gpu/drm/hisilicon/hibmc/dp/dp_hw.h
>>>> @@ -50,6 +50,7 @@ struct hibmc_dp {
>>>>    	struct drm_dp_aux aux;
>>>>    	struct hibmc_dp_cbar_cfg cfg;
>>>>    	u32 irq_status;
>>>> +	int hpd_status;
>>>>    };
>>>>    int hibmc_dp_hw_init(struct hibmc_dp *dp);
>>>> diff --git a/drivers/gpu/drm/hisilicon/hibmc/hibmc_drm_dp.c b/drivers/gpu/drm/hisilicon/hibmc/hibmc_drm_dp.c
>>>> index d06832e62e96..ded38530ecda 100644
>>>> --- a/drivers/gpu/drm/hisilicon/hibmc/hibmc_drm_dp.c
>>>> +++ b/drivers/gpu/drm/hisilicon/hibmc/hibmc_drm_dp.c
>>>> @@ -34,9 +34,12 @@ static int hibmc_dp_connector_get_modes(struct drm_connector *connector)
>>>>    static int hibmc_dp_detect(struct drm_connector *connector,
>>>>    			   struct drm_modeset_acquire_ctx *ctx, bool force)
>>>>    {
>>>> -	mdelay(200);
>>>> +	struct hibmc_dp *dp = to_hibmc_dp(connector);
>>>> -	return drm_connector_helper_detect_from_ddc(connector, ctx, force);
>>>> +	if (dp->hpd_status)
>>>> +		return connector_status_connected;
>>>> +	else
>>>> +		return connector_status_disconnected;
>>>>    }
>>>>    static const struct drm_connector_helper_funcs hibmc_dp_conn_helper_funcs = {
>>>> @@ -115,21 +118,23 @@ irqreturn_t hibmc_dp_hpd_isr(int irq, void *arg)
>>>>    {
>>>>    	struct drm_device *dev = (struct drm_device *)arg;
>>>>    	struct hibmc_drm_private *priv = to_hibmc_drm_private(dev);
>>>> +	struct hibmc_dp *dp = &priv->dp;
>>>>    	int idx;
>>>>    	if (!drm_dev_enter(dev, &idx))
>>>>    		return -ENODEV;
>>>> -	if (priv->dp.irq_status & DP_MASKED_SINK_HPD_PLUG_INT) {
>>>> +	if (((dp->irq_status & DP_MASKED_SINK_HPD_PLUG_INT) && !dp->hpd_status)) {
>>>>    		drm_dbg_dp(&priv->dev, "HPD IN isr occur!\n");
>>>> -		hibmc_dp_hpd_cfg(&priv->dp);
>>>> +		hibmc_dp_hpd_cfg(dp);
>>>> +		dp->hpd_status = 1;
>>>>    	} else {
>>>>    		drm_dbg_dp(&priv->dev, "HPD OUT isr occur!\n");
>>>> -		hibmc_dp_reset_link(&priv->dp);
>>>> +		hibmc_dp_reset_link(dp);
>>>> +		dp->hpd_status = 0;
>>>>    	}
>>>> -	if (dev->registered)
>>>> -		drm_connector_helper_hpd_irq_event(&priv->dp.connector);
>>>> +	drm_connector_helper_hpd_irq_event(&priv->dp.connector);
>>>>    	drm_dev_exit(idx);
>>>> -- 
>>>> 2.33.0
>>>>