From: Doug Anderson <dianders@chromium.org>
To: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Cc: Sankeerth Billakanti <quic_sbillaka@quicinc.com>,
dri-devel <dri-devel@lists.freedesktop.org>,
linux-arm-msm <linux-arm-msm@vger.kernel.org>,
freedreno <freedreno@lists.freedesktop.org>,
LKML <linux-kernel@vger.kernel.org>,
"open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS"
<devicetree@vger.kernel.org>, Rob Clark <robdclark@gmail.com>,
Sean Paul <seanpaul@chromium.org>,
Stephen Boyd <swboyd@chromium.org>,
quic_kalyant <quic_kalyant@quicinc.com>,
"Abhinav Kumar (QUIC)" <quic_abhinavk@quicinc.com>,
"Kuogee Hsieh (QUIC)" <quic_khsieh@quicinc.com>,
Bjorn Andersson <bjorn.andersson@linaro.org>,
Sean Paul <sean@poorly.run>, David Airlie <airlied@linux.ie>,
Daniel Vetter <daniel@ffwll.ch>,
quic_vproddut <quic_vproddut@quicinc.com>,
"Aravind Venkateswaran (QUIC)" <quic_aravindh@quicinc.com>
Subject: Re: [PATCH v6 1/8] drm/msm/dp: Add eDP support via aux_bus
Date: Tue, 5 Apr 2022 11:11:40 -0700 [thread overview]
Message-ID: <CAD=FV=Uibu-kZyix7K4_WVc-+C8xpzTqU4WFy7O=6sukMZrX5g@mail.gmail.com> (raw)
In-Reply-To: <3e5fa57f-d636-879a-b98f-77323d07c156@linaro.org>
Hi,
On Tue, Apr 5, 2022 at 10:36 AM Dmitry Baryshkov
<dmitry.baryshkov@linaro.org> wrote:
>
> On 05/04/2022 20:02, Doug Anderson wrote:
> > Hi,
> >
> > On Tue, Apr 5, 2022 at 5:54 AM Dmitry Baryshkov
> > <dmitry.baryshkov@linaro.org> wrote:
> >>> 3. For DP and eDP HPD means something a little different. Essentially
> >>> there are two concepts: a) is a display physically connected and b) is
> >>> the display powered up and ready. For DP, the two are really tied
> >>> together. From the kernel's point of view you never "power down" a DP
> >>> display and you can't detect that it's physically connected until it's
> >>> ready. Said another way, on you tie "is a display there" to the HPD
> >>> line and the moment a display is there it's ready for you to do AUX
> >>> transfers. For eDP, in the lowest power state of a display it _won't_
> >>> assert its "HPD" signal. However, it's still physically present. For
> >>> eDP you simply have to _assume_ it's present without any actual proof
> >>> since you can't get proof until you power it up. Thus for eDP, you
> >>> report that the display is there as soon as we're asked. We can't
> >>> _talk_ to the display yet, though. So in get_modes() we need to be
> >>> able to power the display on enough to talk over the AUX channel to
> >>> it. As part of this, we wait for the signal named "HPD" which really
> >>> means "panel finished powering on" in this context.
> >>>
> >>> NOTE: for aux transfer, we don't have the _display_ pipe and clocks
> >>> running. We only have enough stuff running to do the AUX transfer.
> >>> We're not clocking out pixels. We haven't fully powered on the
> >>> display. The AUX transfer is designed to be something that can be done
> >>> early _before_ you turn on the display.
> >>>
> >>>
> >>> OK, so basically that was a longwinded way of saying: yes, we could
> >>> avoid the AUX transfer in probe, but we can't wait all the way to
> >>> enable. We have to be able to transfer in get_modes(). If you think
> >>> that's helpful I think it'd be a pretty easy patch to write even if it
> >>> would look a tad bit awkward IMO. Let me know if you want me to post
> >>> it up.
> >>
> >> I think it would be a good idea. At least it will allow us to judge,
> >> which is the more correct way.
> >
> > I'm still happy to prototype this, but the more I think about it the
> > more it feels like a workaround for the Qualcomm driver. The eDP panel
> > driver is actually given a pointer to the AUX bus at probe time. It's
> > really weird to say that we can't do a transfer on it yet... As you
> > said, this is a little sideband bus. It should be able to be used
> > without all the full blown infra of the rest of the driver.
>
> Yes, I have that feeling too. However I also have a feeling that just
> powering up the PHY before the bus probe is ... a hack. There are no
> obvious stopgaps for the driver not to power it down later.
This is why I think we need to move to Runtime PM to manage this. Basically:
1. When an AUX transfer happens, you grab a PM runtime reference that
_that_ powers up the PHY.
2. At the end of the AUX transfer function, you do a "put_autosuspend".
Then it becomes not a hack, right?
> A cleaner design might be to split all hotplug event handling from the
> dp_display, provide a lightweight state machine for the eDP and select
> which state machine to use depending on the hardware connector type. The
> dp_display_bind/unbind would probably also be duplicated and receive
> correct code flows for calling dp_parser_get_next_bridge, etc.
> Basically that means that depending on the device data we'd use either
> dp_display_comp_ops or (new) edp_comp_ops.
>
> WDYT?
I don't think I know the structure of the MSM DP code to make a
definitive answer here. I think I'd have to see a patch. However I'd
agree in general terms that we need some different flows for the two.
;-) We definitely want to limit the differences but some of them will
be unavoidable...
-Doug
next prev parent reply other threads:[~2022-04-05 20:15 UTC|newest]
Thread overview: 70+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-03-30 16:02 [PATCH v6 0/8] Add support for the eDP panel over aux_bus Sankeerth Billakanti
2022-03-30 16:02 ` [PATCH v6 1/8] drm/msm/dp: Add eDP support via aux_bus Sankeerth Billakanti
2022-03-30 23:19 ` Dmitry Baryshkov
2022-03-31 0:33 ` Doug Anderson
2022-03-31 23:22 ` Doug Anderson
2022-04-02 10:37 ` Dmitry Baryshkov
2022-04-02 17:06 ` Doug Anderson
2022-04-02 20:26 ` Dmitry Baryshkov
2022-04-04 20:53 ` Doug Anderson
2022-04-05 12:53 ` Dmitry Baryshkov
2022-04-05 17:02 ` Doug Anderson
2022-04-05 17:36 ` Dmitry Baryshkov
2022-04-05 18:11 ` Doug Anderson [this message]
2022-04-07 14:19 ` Sankeerth Billakanti (QUIC)
2022-04-07 17:07 ` Doug Anderson
2022-04-07 20:11 ` Abhinav Kumar
2022-04-07 20:47 ` Doug Anderson
2022-04-07 22:03 ` Abhinav Kumar
2022-04-07 23:34 ` Doug Anderson
2022-04-07 23:46 ` Dmitry Baryshkov
2022-04-08 0:21 ` Doug Anderson
2022-04-08 12:19 ` Dmitry Baryshkov
2022-04-08 13:43 ` Doug Anderson
2022-04-08 14:58 ` Dmitry Baryshkov
2022-04-08 17:23 ` Abhinav Kumar
2022-04-07 23:35 ` Dmitry Baryshkov
2022-04-08 0:20 ` Doug Anderson
2022-04-08 12:13 ` Dmitry Baryshkov
2022-04-08 13:56 ` Doug Anderson
2022-04-08 14:17 ` Dmitry Baryshkov
2022-03-30 16:02 ` [PATCH v6 2/8] drm/msm/dp: wait for hpd high before aux transaction Sankeerth Billakanti
2022-03-31 23:22 ` Doug Anderson
2022-04-04 12:43 ` Sankeerth Billakanti (QUIC)
2022-03-30 16:02 ` [PATCH v6 3/8] drm/msm/dp: Support only IRQ_HPD and REPLUG interrupts for eDP Sankeerth Billakanti
2022-03-31 23:22 ` Doug Anderson
2022-04-04 12:56 ` Sankeerth Billakanti (QUIC)
2022-03-30 16:02 ` [PATCH v6 4/8] drm/msm/dp: avoid handling masked interrupts Sankeerth Billakanti
2022-03-30 22:16 ` Dmitry Baryshkov
2022-03-31 5:53 ` Sankeerth Billakanti (QUIC)
2022-03-31 10:10 ` Dmitry Baryshkov
2022-03-31 11:04 ` Sankeerth Billakanti
2022-03-31 11:06 ` Dmitry Baryshkov
2022-04-04 17:56 ` Sankeerth Billakanti (QUIC)
2022-03-30 16:02 ` [PATCH v6 5/8] drm/msm/dp: prevent multiple votes for dp resources Sankeerth Billakanti
2022-03-31 23:23 ` Doug Anderson
2022-04-08 16:14 ` Dmitry Baryshkov
2022-04-08 17:12 ` Sankeerth Billakanti
2022-04-08 18:02 ` Dmitry Baryshkov
2022-03-30 16:02 ` [PATCH v6 6/8] drm/msm/dp: remove unnecessary delay during boot Sankeerth Billakanti
2022-03-31 23:23 ` Doug Anderson
2022-04-04 13:52 ` Sankeerth Billakanti (QUIC)
2022-04-04 21:13 ` Dmitry Baryshkov
2022-04-07 12:40 ` Sankeerth Billakanti (QUIC)
2022-03-30 16:02 ` [PATCH v6 7/8] drm/msm/dp: Support edp/dp without hpd Sankeerth Billakanti
2022-03-31 23:23 ` Doug Anderson
2022-04-04 18:32 ` Sankeerth Billakanti (QUIC)
2022-04-04 21:15 ` Dmitry Baryshkov
2022-04-07 12:41 ` Sankeerth Billakanti (QUIC)
2022-03-30 16:02 ` [PATCH v6 8/8] drm/msm/dp: Handle eDP mode_valid differently from dp Sankeerth Billakanti
2022-03-30 22:08 ` Dmitry Baryshkov
2022-03-31 6:02 ` Sankeerth Billakanti (QUIC)
2022-03-31 23:24 ` Doug Anderson
2022-04-04 18:20 ` Sankeerth Billakanti (QUIC)
2022-04-04 21:29 ` Dmitry Baryshkov
2022-04-07 14:05 ` Sankeerth Billakanti (QUIC)
2022-04-08 12:08 ` Dmitry Baryshkov
2022-04-08 15:50 ` Sankeerth Billakanti
2022-04-08 16:47 ` Dmitry Baryshkov
2022-04-08 17:38 ` Sankeerth Billakanti
2022-04-08 18:06 ` Dmitry Baryshkov
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