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Feedback-ID: i8771445c:Fastmail
Date:   Mon, 14 Nov 2022 14:06:08 +0100
From:   Maxime Ripard <maxime@cerno.tech>
To:     Stefan Wahren <stefan.wahren@i2se.com>
Cc:     David Airlie <airlied@linux.ie>, Daniel Vetter <daniel@ffwll.ch>,
        Thomas Zimmermann <tzimmermann@suse.de>,
        Maarten Lankhorst <maarten.lankhorst@linux.intel.com>,
        Emma Anholt <emma@anholt.net>, dri-devel@lists.freedesktop.org,
        linux-kernel@vger.kernel.org,
        Marc Kleine-Budde <mkl@pengutronix.de>
Subject: Re: [PATCH 1/2] drm/vc4: hdmi: Enforce the minimum rate at
 runtime_resume
Message-ID: <20221114130608.kqxhorlee25rvrc7@houat>
References: <20220929-rpi-pi3-unplugged-fixes-v1-0-cd22e962296c@cerno.tech>
 <20220929-rpi-pi3-unplugged-fixes-v1-1-cd22e962296c@cerno.tech>
 <737e7e23-1bc5-eaf3-2d15-5498fc5b0415@i2se.com>
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Hi Stefan,

On Mon, Nov 14, 2022 at 01:48:14AM +0100, Stefan Wahren wrote:
> Am 11.11.22 um 22:08 schrieb Stefan Wahren:
> > Hi Maxime,
> >=20
> > Am 29.09.22 um 11:21 schrieb Maxime Ripard:
> > > This is a revert of commit fd5894fa2413 ("drm/vc4: hdmi: Remove clock
> > > rate initialization"), with the code slightly moved around.
> > >=20
> > > It turns out that we can't downright remove that code from the driver,
> > > since the Pi0-3 and Pi4 are in different cases, and it only works for
> > > the Pi4.
> > >=20
> > > Indeed, the commit mentioned above was relying on the RaspberryPi
> > > firmware clocks driver to initialize the rate if it wasn't done by the
> > > firmware. However, the Pi0-3 are using the clk-bcm2835 clock driver t=
hat
> > > wasn't doing this initialization. We therefore end up with the clock =
not
> > > being assigned a rate, and the CPU stalling when trying to access a
> > > register.
> > >=20
> > > We can't move that initialization in the clk-bcm2835 driver, since the
> > > HSM clock we depend on is actually part of the HDMI power domain, so =
any
> > > rate setup is only valid when the power domain is enabled. Thus, we
> > > reinstated the minimum rate setup at runtime_suspend, which should
> > > address both issues.
> > >=20
> > > Link: https://lore.kernel.org/dri-devel/20220922145448.w3xfywkn5ecak2=
et@pengutronix.de/
> > > Fixes: fd5894fa2413 ("drm/vc4: hdmi: Remove clock rate initialization=
")
> > > Reported-by: Marc Kleine-Budde <mkl@pengutronix.de>
> > > Signed-off-by: Maxime Ripard <maxime@cerno.tech>
> > > ---
> > > =A0 drivers/gpu/drm/vc4/vc4_hdmi.c | 9 +++++++++
> > > =A0 1 file changed, 9 insertions(+)
> > >=20
> > > diff --git a/drivers/gpu/drm/vc4/vc4_hdmi.c
> > > b/drivers/gpu/drm/vc4/vc4_hdmi.c
> > > index 199bc398817f..2e28fe16ed5e 100644
> > > --- a/drivers/gpu/drm/vc4/vc4_hdmi.c
> > > +++ b/drivers/gpu/drm/vc4/vc4_hdmi.c
> > > @@ -2891,6 +2891,15 @@ static int vc4_hdmi_runtime_resume(struct
> > > device *dev)
> > > =A0=A0=A0=A0=A0 u32 __maybe_unused value;
> > > =A0=A0=A0=A0=A0 int ret;
> > > =A0 +=A0=A0=A0 /*
> > > +=A0=A0=A0=A0 * The HSM clock is in the HDMI power domain, so we need=
 to set
> > > +=A0=A0=A0=A0 * its frequency while the power domain is active so tha=
t it
> > > +=A0=A0=A0=A0 * keeps its rate.
> > > +=A0=A0=A0=A0 */
> > > +=A0=A0=A0 ret =3D clk_set_min_rate(vc4_hdmi->hsm_clock, HSM_MIN_CLOC=
K_FREQ);
> > > +=A0=A0=A0 if (ret)
> > > +=A0=A0=A0=A0=A0=A0=A0 return ret;
> > > +
> >=20
> > unfortunately this breaks X on Raspberry Pi 4 in Linux 6.0.5
> > (multi_v7_defconfig + LPAE). Today i saw this report [1] and bisected
> > the issue down to this patch. Shame on me that i only tested this patch
> > with Rpi 3B+ :-(
>
> Looks like "drm/vc4: hdmi: Fix HSM clock too low on Pi4" addresses this
> issue ...

Yes, indeed. The fix should be on its way to -stable already

Maxime

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