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From: Bjorn Andersson <bjorn.andersson@linaro.org>
To: Hans de Goede <hdegoede@redhat.com>
Cc: Heikki Krogerus <heikki.krogerus@linux.intel.com>,
	Imre Deak <imre.deak@intel.com>,
	Prashant Malani <pmalani@chromium.org>,
	Doug Anderson <dianders@chromium.org>,
	Laurent Pinchart <laurent.pinchart@ideasonboard.com>,
	Rob Clark <robdclark@gmail.com>, Sean Paul <sean@poorly.run>,
	David Airlie <airlied@linux.ie>, Daniel Vetter <daniel@ffwll.ch>,
	linux-arm-msm <linux-arm-msm@vger.kernel.org>,
	LKML <linux-kernel@vger.kernel.org>,
	Abhinav Kumar <abhinavk@codeaurora.org>,
	Stephen Boyd <swboyd@chromium.org>,
	Kuogee Hsieh <khsieh@codeaurora.org>,
	dri-devel <dri-devel@lists.freedesktop.org>,
	Vara Reddy <varar@codeaurora.org>,
	freedreno <freedreno@lists.freedesktop.org>,
	Enric Balletbo i Serra <enric.balletbo@collabora.com>,
	Benson Leung <bleung@chromium.org>
Subject: Re: [RFC] drm/msm/dp: Allow attaching a drm_panel
Date: Tue, 7 Dec 2021 09:29:54 -0800	[thread overview]
Message-ID: <Ya+aEr+XWTjdcTt9@ripper> (raw)
In-Reply-To: <1932c73c-e372-788b-fcbd-13cad52d96da@redhat.com>

On Tue 07 Dec 08:56 PST 2021, Hans de Goede wrote:

> Hi all,
> 
> On 12/7/21 13:26, Heikki Krogerus wrote:
> > +Hans and Imre
> > 
> > On Mon, Dec 06, 2021 at 02:31:40PM -0800, Bjorn Andersson wrote:
> >> On Thu 07 Oct 03:17 PDT 2021, Heikki Krogerus wrote:
> >>> On Wed, Oct 06, 2021 at 01:26:35PM -0700, Prashant Malani wrote:
> >>>> (CC+ Heikki)
> >> [..]
> >>>> On Wed, Oct 6, 2021 at 8:19 AM Doug Anderson <dianders@chromium.org> wrote:
> >> [..]
> >>>         void drm_connector_oob_hotplug_event(struct fwnode_handle *connector_fwnode);
> >>>
> >>> If your USB Type-C controller/port driver does not yet register the DP
> >>> alt mode, the it's responsible of handling HPD separately by calling
> >>> drm_connector_oob_hotplug_event() on its own.
> >>>
> >>
> >> Finally found my way back to this topic and it doesn't look like I can
> >> reuse the existing altmode code with the firmware interface provided by
> >> Qualcomm, so  I just hacked something up that invokes
> >> drm_connector_oob_hotplug_event().
> >>
> >> But I'm not able to make sense of what the expected usage is. Reading
> >> altmode/displayport.c, it seems that I should only invoke
> >> drm_connector_oob_hotplug_event() as HPD state toggles.
> >>
> >> I made a trial implementation of this, where my firmware interface
> >> driver calls drm_connector_oob_hotplug_event() every time HPD state
> >> changes and then in my oob_hotplug_event callback I flip the DP
> >> controller between on and off.
> >>
> >> Unfortunately when I then connect my HDMI dongle, I get HPD state HIGH,
> >> call the oob_hotplug_event, the DP driver powers up and concludes that
> >> there's nothing connected to the dongle and goes to idle. I then connect
> >> the HDMI cable to the dongle, the firmware sends me another message with
> >> HPD irq and state HIGH, which I ignore because it's not a change in
> >> state.
> >>
> >> In the end I hacked up drm_connector_oob_hotplug_event() to allow me to
> >> pass the HPD state and this solves my problem. I can now distinguish
> >> between connect, disconnect and attention.
> >>
> >> Can you please help shed some light on what I might be missing?
> 
> The plan always was to pass some extra information, like the number
> of available DP lanes (which can make training faster) along as
> parameter to the drm_connector_oob_hotplug_event().
> 
> The merged version ended up not doing this because there were no
> consumers, but passing additional info like HPD state definitely
> is ok.
> 

Thanks, that clarifies things.

I think it makes sense to pass #lanes, as that would rule out the
possibility of attempting to run 4 lanes per dpcd information over a
2-lane mux configuration as well.

I will write up some patches.

Regards,
Bjorn

  reply	other threads:[~2021-12-07 17:28 UTC|newest]

Thread overview: 28+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-07-26 23:13 Bjorn Andersson
2021-07-29  9:59 ` Dmitry Baryshkov
2021-08-25 23:28   ` Bjorn Andersson
2021-08-26  1:31 ` Stephen Boyd
2021-08-26 20:36   ` Doug Anderson
2021-08-26 20:29 ` Doug Anderson
2021-08-27 20:52 ` Doug Anderson
2021-08-28 14:40   ` Bjorn Andersson
2021-08-30 16:01     ` Doug Anderson
2021-10-01 21:02   ` Bjorn Andersson
2021-10-05  0:36     ` Doug Anderson
2021-10-05  1:11       ` Bjorn Andersson
2021-10-05  1:50         ` Stephen Boyd
2021-10-05  2:11           ` Bjorn Andersson
2021-10-05 15:39         ` Doug Anderson
2021-10-05 17:34           ` Bjorn Andersson
2021-10-05 23:09             ` Doug Anderson
2021-10-06  2:29               ` Bjorn Andersson
2021-10-06 15:12                 ` Doug Anderson
2021-10-06 20:26                   ` Prashant Malani
2021-10-07 10:17                     ` Heikki Krogerus
2021-10-07 16:15                       ` Bjorn Andersson
2021-10-08 12:38                         ` Heikki Krogerus
2021-12-06 22:31                       ` Bjorn Andersson
2021-12-07 12:26                         ` Heikki Krogerus
2021-12-07 16:56                           ` Hans de Goede
2021-12-07 17:29                             ` Bjorn Andersson [this message]
2021-12-07 17:54                           ` Imre Deak

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