linux-kernel - Re: [PATCH v4 7/7] drm/vc4: Make sure we don't end up with a core clock too high

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Message-ID: <CAPY8ntDvg4Ei-b=adWHi5A8BKamd53Q3FnoyOXvW5zeuYyLArg@mail.gmail.com>
Date:   Wed, 26 Oct 2022 17:09:31 +0100
From:   Dave Stevenson <dave.stevenson@...pberrypi.com>
To:     maxime@...no.tech
Cc:     Daniel Vetter <daniel@...ll.ch>, Emma Anholt <emma@...olt.net>,
        Michael Turquette <mturquette@...libre.com>,
        Stephen Boyd <sboyd@...nel.org>,
        Maxime Ripard <mripard@...nel.org>,
        Ray Jui <rjui@...adcom.com>,
        Florian Fainelli <f.fainelli@...il.com>,
        David Airlie <airlied@...ux.ie>,
        Broadcom internal kernel review list 
        <bcm-kernel-feedback-list@...adcom.com>,
        Scott Branden <sbranden@...adcom.com>,
        Stefan Wahren <stefan.wahren@...e.com>,
        linux-kernel@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        Dom Cobley <popcornmix@...il.com>, linux-clk@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org,
        linux-rpi-kernel@...ts.infradead.org
Subject: Re: [PATCH v4 7/7] drm/vc4: Make sure we don't end up with a core
 clock too high

On Thu, 20 Oct 2022 at 10:14, <maxime@...no.tech> wrote:
>
> Following the clock rate range improvements to the clock framework,
> trying to set a disjoint range on a clock will now result in an error.
>
> Thus, we can't set a minimum rate higher than the maximum reported by
> the firmware, or clk_set_min_rate() will fail.
>
> Thus we need to clamp the rate we are about to ask for to the maximum
> rate possible on that clock.
>
> Signed-off-by: Maxime Ripard <maxime@...no.tech>

Thanks Maxime.

Reviewed-by: Dave Stevenson <dave.stevenson@...pberrypi.com>

> ---
>  drivers/gpu/drm/vc4/vc4_kms.c | 13 ++++++++-----
>  1 file changed, 8 insertions(+), 5 deletions(-)
>
> diff --git a/drivers/gpu/drm/vc4/vc4_kms.c b/drivers/gpu/drm/vc4/vc4_kms.c
> index 4419e810103d..5c97642ed66a 100644
> --- a/drivers/gpu/drm/vc4/vc4_kms.c
> +++ b/drivers/gpu/drm/vc4/vc4_kms.c
> @@ -396,8 +396,8 @@ static void vc4_atomic_commit_tail(struct drm_atomic_state *state)
>         if (vc4->is_vc5) {
>                 unsigned long state_rate = max(old_hvs_state->core_clock_rate,
>                                                new_hvs_state->core_clock_rate);
> -               unsigned long core_rate = max_t(unsigned long,
> -                                               500000000, state_rate);
> +               unsigned long core_rate = clamp_t(unsigned long, state_rate,
> +                                                 500000000, hvs->max_core_rate);
>
>                 drm_dbg(dev, "Raising the core clock at %lu Hz\n", core_rate);
>
> @@ -431,14 +431,17 @@ static void vc4_atomic_commit_tail(struct drm_atomic_state *state)
>         drm_atomic_helper_cleanup_planes(dev, state);
>
>         if (vc4->is_vc5) {
> -               drm_dbg(dev, "Running the core clock at %lu Hz\n",
> -                       new_hvs_state->core_clock_rate);
> +               unsigned long core_rate = min_t(unsigned long,
> +                                               hvs->max_core_rate,
> +                                               new_hvs_state->core_clock_rate);
> +
> +               drm_dbg(dev, "Running the core clock at %lu Hz\n", core_rate);
>
>                 /*
>                  * Request a clock rate based on the current HVS
>                  * requirements.
>                  */
> -               WARN_ON(clk_set_min_rate(hvs->core_clk, new_hvs_state->core_clock_rate));
> +               WARN_ON(clk_set_min_rate(hvs->core_clk, core_rate));
>
>                 drm_dbg(dev, "Core clock actual rate: %lu Hz\n",
>                         clk_get_rate(hvs->core_clk));
>
> --
> b4 0.10.1