linux-kernel - Re: [PATCH v3 drm-dp 7/8] drm/hisilicon/hibmc: Enable this hot plug detect of irq feature

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Message-ID: <4hicem4rbz5l7wnzaaz3krrl3euh2dmvlah2rb7errrdq5fann@44dvdxirkuzh>
Date: Thu, 27 Feb 2025 17:38:41 +0200
From: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
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, lidongming5@...wei.com, libaihan@...wei.com, 
	shenjian15@...wei.com, shaojijie@...wei.com, dri-devel@...ts.freedesktop.org, 
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 drm-dp 7/8] drm/hisilicon/hibmc: Enable this hot plug
 detect of irq feature

On Thu, Feb 27, 2025 at 09:46:10PM +0800, Yongbang Shi wrote:
> 
> > On Tue, Feb 25, 2025 at 09:57:17PM +0800, Yongbang Shi wrote:
> > > > On Mon, 24 Feb 2025 at 16:03, Yongbang Shi <shiyongbang@...wei.com> wrote:
> > > > > > On Sat, Feb 22, 2025 at 06:35:48PM +0800, Yongbang Shi wrote:
> > > > > > > > > +static int hibmc_dp_hpd_event(struct drm_client_dev *client)
> > > > > > > > > +{
> > > > > > > > > +  struct hibmc_dp *dp = container_of(client, struct hibmc_dp, client);
> > > > > > > > > +  struct hibmc_drm_private *priv = to_hibmc_drm_private(dp->drm_dev);
> > > > > > > > > +  struct drm_display_mode *mode = &priv->crtc.state->adjusted_mode;
> > > > > > > > > +  int ret;
> > > > > > > > > +
> > > > > > > > > +  if (dp->hpd_status) {
> > > > > > > > > +          hibmc_dp_hpd_cfg(&priv->dp);
> > > > > > > > > +          ret = hibmc_dp_prepare(dp, mode);
> > > > > > > > > +          if (ret)
> > > > > > > > > +                  return ret;
> > > > > > > > > +
> > > > > > > > > +          hibmc_dp_display_en(dp, true);
> > > > > > > > > +  } else {
> > > > > > > > > +          hibmc_dp_display_en(dp, false);
> > > > > > > > > +          hibmc_dp_reset_link(&priv->dp);
> > > > > > > > > +  }
> > > > > > > > If I understand this correctly, you are using a separate drm_client to
> > > > > > > > enable and disable the link & display. Why is it necessary? Existing
> > > > > > > > drm_clients and userspace compositors use drm framework, they should be
> > > > > > > > able to turn the display on and off as required.
> > > > > > > > 
> > > > > > > Thanks for your asking, there are cfg/reset process when the connector 's pluging in/out.
> > > > > > > We want to cfg DP registers again when the connector changes. Not only dp link training, but also cfg
> > > > > > > the different video modes into DP registers.
> > > > > > Why? The link training and mode programming should happen during
> > > > > > pre_enable / enable stage (legacy or atomic).
> > > > > Hi Dmitry,
> > > > > 
> > > > > Right, that's what I'm curious about. It won't call encoder enble/disable functions when I triggered HPD.
> > > > > And I'm sure the drm_connector_helper_hpd_irq_event() is called. So I add a drm_client for it.I
> > > > It should be userspace, who triggers the enable/disable (or it should
> > > > be the in-kernel fbdev / fbcon, which interface through the generic
> > > > drm_fbdev client).
> > > Right, I knew it. When I insmode my driver firstly (or restart display service), it will call disable, modeset and enable,
> > > by user, but it won't call when HPD triggered .
> > - Is HPD even properly delivered to userspace? What kind of compsitor
> >    are you using? Is .detect working properly and reporting a correct
> >    plug-in state?
> 
> Thanks for your answering. I'm not very good understanding about userspace in framework. In my opinion, when I call
> this drm_connector_helper_hpd_irq_event(), the HPD will deliver to userspace.
> I use Xorg, and the display service is GDM.
> The .detect is called and the getting modes info is correct.
> I find that it would only trigger(disable, modeset and enable), when I changed resolutions, restart display service and insmod driver.

You can go to the display settings in GDM. It would be interesting to
observe if it notes the second monitor or not. Last, but not least, you
can use a simple tool like 'xrandr' under your XOrg session to set the
display resolution.

-- 
With best wishes
Dmitry