linux-kernel - Re: [PATCH] drm/bridge_connector: enable HPD by default if supported

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Message-ID: <CAMSo37XPdLcVQnRdfL3y4kz82gftg2My0Dvd937GW=N9MiqURA@mail.gmail.com>
Date:   Wed, 12 Apr 2023 02:52:40 +0800
From:   Yongqin Liu <yongqin.liu@...aro.org>
To:     Tomi Valkeinen <tomi.valkeinen@...asonboard.com>
Cc:     Kieran Bingham <kieran.bingham+renesas@...asonboard.com>,
        Laurent Pinchart <laurent.pinchart@...asonboard.com>,
        Nikita Yushchenko <nikita.yoush@...entembedded.com>,
        Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Maxime Ripard <mripard@...nel.org>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        Jacopo Mondi <jacopo+renesas@...ndi.org>,
        dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] drm/bridge_connector: enable HPD by default if supported

HI, All

Just an updated here.
As the commits listed the the following link merged into the
android-mainline kernel:
    https://lore.kernel.org/linux-arm-kernel/20221102180705.459294-1-dmitry.baryshkov@linaro.org/T/
The problem caused by this commit with x15 build is gone now.

Thanks,
Yongqin Liu
On Mon, 5 Sept 2022 at 13:26, Tomi Valkeinen
<tomi.valkeinen@...asonboard.com> wrote:
>
> On 31/08/2022 16:02, Tomi Valkeinen wrote:
> > Hi,
> >
> > On 23/02/2022 19:02, Kieran Bingham wrote:
> >> Quoting Laurent Pinchart (2022-02-23 16:25:28)
> >>> Hello,
> >>>
> >>> On Wed, Feb 23, 2022 at 04:17:22PM +0000, Kieran Bingham wrote:
> >>>> Quoting Laurent Pinchart (2021-12-29 23:44:29)
> >>>>> On Sat, Dec 25, 2021 at 09:31:51AM +0300, Nikita Yushchenko wrote:
> >>>>>> Hotplug events reported by bridge drivers over
> >>>>>> drm_bridge_hpd_notify()
> >>>>>> get ignored unless somebody calls drm_bridge_hpd_enable(). When the
> >>>>>> connector for the bridge is bridge_connector, such a call is done
> >>>>>> from
> >>>>>> drm_bridge_connector_enable_hpd().
> >>>>>>
> >>>>>> However drm_bridge_connector_enable_hpd() is never called on init
> >>>>>> paths,
> >>>>>> documentation suggests that it is intended for suspend/resume paths.
> >>>>>
> >>>>> Hmmmm... I'm in two minds about this. The problem description is
> >>>>> correct, but I wonder if HPD should be enabled unconditionally
> >>>>> here, or
> >>>>> if this should be left to display drivers to control.
> >>>>> drivers/gpu/drm/imx/dcss/dcss-kms.c enables HPD manually at init time,
> >>>>> other drivers don't.
> >>>>>
> >>>>> It feels like this should be under control of the display controller
> >>>>> driver, but I can't think of a use case for not enabling HPD at init
> >>>>> time. Any second opinion from anyone ?
> >>>>
> >>>> This patch solves an issue I have where I have recently enabled HPD on
> >>>> the SN65DSI86, but without this, I do not get calls to my
> >>>> .hpd_enable or
> >>>> .hpd_disable hooks that I have added to the ti_sn_bridge_funcs.
> >>>>
> >>>> So it needs to be enabled somewhere, and this seems reasonable to me?
> >>>> It's not directly related to the display controller - as it's a factor
> >>>> of the bridge?
> >>>>
> >>>> On Falcon-V3U with HPD additions to SN65DSI86:
> >>>> Tested-by: Kieran Bingham <kieran.bingham+renesas@...asonboard.com>
> >>>
> >>> If you think this is right, then
> >>>
> >>> Reviewed-by: Laurent Pinchart <laurent.pinchart@...asonboard.com>
> >>
> >> I do, and at the very least it works for me, and fixes Nikita's issue so
> >> to me that's enough for:
> >
> > So who disables the HPD now?
> >
> > Is the drm_bridge_connector_enable_hpd &
> > drm_bridge_connector_disable_hpd documentation now wrong as they talk
> > about suspend/resume handlers?
>
> To give more context, currently omapdrm enables the HPDs at init time
> and disables them at remove time. With this patch, the HPDs are enabled
> twice, leading to a WARN.
>
> imx and msm drivers also seem to call drm_bridge_connector_enable_hpd(),
> so I would guess those also WARN with this patch.
>
> Afaics, this patch alone is broken, as it just disregards the drivers
> that already enable the HPD, and also as it doesn't handle the disabling
> of the HPD, or give any guidelines on how the drivers should now manage
> the HPD.
>
> My suggestion is to revert this one.
>
>   Tomi


-- 
Best Regards,
Yongqin Liu
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