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Message-ID: <be19509a-3e9a-e2a9-24c5-0aac74987942@redhat.com>
Date: Thu, 13 Oct 2022 11:37:57 +0200
From: Javier Martinez Canillas <javierm@...hat.com>
To: Maxime Ripard <maxime@...no.tech>, David Airlie <airlied@...ux.ie>,
Daniel Vetter <daniel@...ll.ch>,
Thomas Zimmermann <tzimmermann@...e.de>,
Maxime Ripard <mripard@...nel.org>,
Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
Emma Anholt <emma@...olt.net>
Cc: Stefan Wahren <stefan.wahren@...e.com>,
Marc Kleine-Budde <mkl@...gutronix.de>,
linux-kernel@...r.kernel.org, dri-devel@...ts.freedesktop.org
Subject: Re: [PATCH 1/2] drm/vc4: hdmi: Enforce the minimum rate at
runtime_resume
Hello Maxime,
On 9/29/22 11:21, Maxime Ripard wrote:
> This is a revert of commit fd5894fa2413 ("drm/vc4: hdmi: Remove clock
> rate initialization"), with the code slightly moved around.
>
> 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.
>
> 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 that
> 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.
>
> 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.
>
> Link: https://lore.kernel.org/dri-devel/20220922145448.w3xfywkn5ecak2et@pengutronix.de/
> Fixes: fd5894fa2413 ("drm/vc4: hdmi: Remove clock rate initialization")
> Reported-by: Marc Kleine-Budde <mkl@...gutronix.de>
> Signed-off-by: Maxime Ripard <maxime@...no.tech>
> ---
> drivers/gpu/drm/vc4/vc4_hdmi.c | 9 +++++++++
> 1 file changed, 9 insertions(+)
>
> 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)
> u32 __maybe_unused value;
> int ret;
>
> + /*
> + * The HSM clock is in the HDMI power domain, so we need to set
> + * its frequency while the power domain is active so that it
> + * keeps its rate.
> + */
> + ret = clk_set_min_rate(vc4_hdmi->hsm_clock, HSM_MIN_CLOCK_FREQ);
> + if (ret)
> + return ret;
> +
I'm not familiar with VC4 but your commit message has a great explanation
of the issue and the code is doing what you mention there. So this patch
looks good to me.
Reviewed-by: Javier Martinez Canillas <javierm@...hat.com>
--
Best regards,
Javier Martinez Canillas
Core Platforms
Red Hat
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