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: <13b3f4d9-c8b4-445f-8f9e-a57a1fa2bbb5@huawei.com>
Date: Fri, 12 Sep 2025 09:23:05 +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, Sep 11, 2025 at 05:32:40PM +0800, Yongbang Shi wrote:
>>> 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?
>> I'm very sorry that I didn't get the last sentence's asking before.
>> It's a non-branch device. We just connect a DP monitor.
> Somebody might connect a different configuration than the one that you
> are using.

Okay, I can add the check drm_dp_is_branch() in the DP's detect_ctx() to
intercept branch devices, is that good?

Thanks,
Baihan Li