linux-kernel - Re: [PATCH v2 2/2] drm/privacy_screen_x86: Add entry for ChromeOS privacy-screen

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Message-ID: <YcD9DkYLrdexyP0p@google.com>
Date:   Mon, 20 Dec 2021 14:00:46 -0800
From:   Dmitry Torokhov <dmitry.torokhov@...il.com>
To:     Rajat Jain <rajatja@...gle.com>
Cc:     Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Maxime Ripard <mripard@...nel.org>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        Hans de Goede <hdegoede@...hat.com>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        Benson Leung <bleung@...omium.org>,
        linux-kernel@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        gwendal@...gle.com, seanpaul@...gle.com, marcheau@...gle.com,
        rajatxjain@...il.com
Subject: Re: [PATCH v2 2/2] drm/privacy_screen_x86: Add entry for ChromeOS
 privacy-screen

On Mon, Dec 20, 2021 at 12:29:18PM -0800, Rajat Jain wrote:
> Hello,
> 
> On Mon, Dec 20, 2021 at 11:50 AM Dmitry Torokhov
> <dmitry.torokhov@...il.com> wrote:
> >
> > On Fri, Dec 17, 2021 at 12:28:50PM -0800, Rajat Jain wrote:
> > > Add a static entry in the x86 table, to detect and wait for
> > > privacy-screen on some ChromeOS platforms.
> > >
> > > Please note that this means that if CONFIG_CHROMEOS_PRIVACY_SCREEN is
> > > enabled, and if "GOOG0010" device is found in ACPI, then the i915 probe
> > > shall return EPROBE_DEFER until a platform driver actually registers the
> > > privacy-screen: https://hansdegoede.livejournal.com/25948.html
> > >
> > > Signed-off-by: Rajat Jain <rajatja@...gle.com>
> > > ---
> > > v2: * Use #if instead of #elif
> > >     * Reorder the patches in the series.
> > >     * Rebased on drm-tip
> > >
> > >  drivers/gpu/drm/drm_privacy_screen_x86.c | 22 ++++++++++++++++++++++
> > >  1 file changed, 22 insertions(+)
> > >
> > > diff --git a/drivers/gpu/drm/drm_privacy_screen_x86.c b/drivers/gpu/drm/drm_privacy_screen_x86.c
> > > index a2cafb294ca6..0c5699ad70a3 100644
> > > --- a/drivers/gpu/drm/drm_privacy_screen_x86.c
> > > +++ b/drivers/gpu/drm/drm_privacy_screen_x86.c
> > > @@ -47,6 +47,18 @@ static bool __init detect_thinkpad_privacy_screen(void)
> > >  }
> > >  #endif
> > >
> > > +#if IS_ENABLED(CONFIG_CHROMEOS_PRIVACY_SCREEN)
> > > +static bool __init detect_chromeos_privacy_screen(void)
> >
> > Does marking this __init work in case there is a deferral?
> 
> Yes, I have verified that for Chromeos case, it is a deferral.
> 
> > Can it happen
> > that privacy screen is a module and so will get loaded only after we
> > discarded __init sections.
> 
> Perhaps. But I do not think that  is a problem. All the functions and
> data in this file are in __init sections, and this entry is here to
> ensure that the drm probe will wait for the privacy screen driver
> (whenever it is loaded).

Ah, OK, we are not leaking detect() pointers outside this module. 

> That is the reason, ideally we  would want to
> somehow restrict the privacy screen to be built into the kernel so as
> to minimize the delay if any.

I understand, but we can not code to the config we expect to use on
Chrome OS, we need to make sure we cover all possibilities.

Thanks.
-- 
Dmitry