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: <3sywcmtd4uksow6exaav6smx4wwrlp7mur6mcrpw3qklvbr3kn@dqypx4fmnhrw>
Date: Fri, 12 Sep 2025 14:25:03 +0300
From: Dmitry Baryshkov <dmitry.baryshkov@....qualcomm.com>
To: Yongbang Shi <shiyongbang@...wei.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
Subject: Re: [PATCH v4 drm-dp 02/11] drm/hisilicon/hibmc: fix dp
 probabilistical detect errors after HPD irq

On Fri, Sep 12, 2025 at 09:23:05AM +0800, Yongbang Shi wrote:
> 
> > 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?

My suggestion is to implement DP detection in the way it's done by other
DP drivers.

-- 
With best wishes
Dmitry