linux-kernel - Re: [PATCH v2 1/5] drm/vc4: hdmi: Make sure the controller is powered up during bind

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Date:   Wed, 28 Jul 2021 14:50:03 +0100
From:   Dave Stevenson <dave.stevenson@...pberrypi.com>
To:     Maxime Ripard <maxime@...no.tech>
Cc:     DRI Development <dri-devel@...ts.freedesktop.org>,
        Daniel Vetter <daniel.vetter@...el.com>,
        David Airlie <airlied@...ux.ie>,
        Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        Maxime Ripard <mripard@...nel.org>,
        Emma Anholt <emma@...olt.net>,
        Boris Brezillon <bbrezillon@...nel.org>,
        Phil Elwell <phil@...pberrypi.com>,
        Tim Gover <tim.gover@...pberrypi.com>,
        Dom Cobley <dom@...pberrypi.com>,
        linux-rpi-kernel@...ts.infradead.org,
        Nicolas Saenz Julienne <nsaenz@...nel.org>,
        Hans Verkuil <hverkuil-cisco@...all.nl>,
        LKML <linux-kernel@...r.kernel.org>,
        bcm-kernel-feedback-list@...adcom.com
Subject: Re: [PATCH v2 1/5] drm/vc4: hdmi: Make sure the controller is powered
 up during bind

Hi Maxime

On Wed, 7 Jul 2021 at 10:23, Maxime Ripard <maxime@...no.tech> wrote:
>
> In the bind hook, we actually need the device to have the HSM clock
> running during the final part of the display initialisation where we
> reset the controller and initialise the CEC component.
>
> Failing to do so will result in a complete, silent, hang of the CPU.
>
> Fixes: 411efa18e4b0 ("drm/vc4: hdmi: Move the HSM clock enable to runtime_pm")
> Signed-off-by: Maxime Ripard <maxime@...no.tech>
> ---
>  drivers/gpu/drm/vc4/vc4_hdmi.c | 17 +++++++++++++++--
>  1 file changed, 15 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/gpu/drm/vc4/vc4_hdmi.c b/drivers/gpu/drm/vc4/vc4_hdmi.c
> index aab1b36ceb3c..dac47b100b8b 100644
> --- a/drivers/gpu/drm/vc4/vc4_hdmi.c
> +++ b/drivers/gpu/drm/vc4/vc4_hdmi.c
> @@ -2176,6 +2176,18 @@ static int vc4_hdmi_bind(struct device *dev, struct device *master, void *data)
>                         vc4_hdmi->disable_4kp60 = true;
>         }
>
> +       /*
> +        * We need to have the device powered up at this point to call
> +        * our reset hook and for the CEC init.
> +        */
> +       ret = vc4_hdmi_runtime_resume(dev);

vc4_hdmi_runtime_resume is within a #ifdef CONFIG_PM block, so
potentially isn't defined.
Admittedly we "select PM" in Kconfig so it should always be enabled,
so perhaps it's better to just remove the #ifdef CONFIG_PM around the
resume and suspend functions.

That's possibly a separate issue to the issue that this patch is
addressing, but may explain the test bot's failure. Otherwise
Reviewed-by: Dave Stevenson <dave.stevenson@...pberrypi.com>

> +       if (ret)
> +               goto err_put_ddc;
> +
> +       pm_runtime_get_noresume(dev);
> +       pm_runtime_set_active(dev);
> +       pm_runtime_enable(dev);
> +
>         if (vc4_hdmi->variant->reset)
>                 vc4_hdmi->variant->reset(vc4_hdmi);
>
> @@ -2187,8 +2199,6 @@ static int vc4_hdmi_bind(struct device *dev, struct device *master, void *data)
>                 clk_prepare_enable(vc4_hdmi->pixel_bvb_clock);
>         }
>
> -       pm_runtime_enable(dev);
> -
>         drm_simple_encoder_init(drm, encoder, DRM_MODE_ENCODER_TMDS);
>         drm_encoder_helper_add(encoder, &vc4_hdmi_encoder_helper_funcs);
>
> @@ -2208,6 +2218,8 @@ static int vc4_hdmi_bind(struct device *dev, struct device *master, void *data)
>                              vc4_hdmi_debugfs_regs,
>                              vc4_hdmi);
>
> +       pm_runtime_put_sync(dev);
> +
>         return 0;
>
>  err_free_cec:
> @@ -2216,6 +2228,7 @@ static int vc4_hdmi_bind(struct device *dev, struct device *master, void *data)
>         vc4_hdmi_connector_destroy(&vc4_hdmi->connector);
>  err_destroy_encoder:
>         drm_encoder_cleanup(encoder);
> +       pm_runtime_put_sync(dev);
>         pm_runtime_disable(dev);
>  err_put_ddc:
>         put_device(&vc4_hdmi->ddc->dev);
> --
> 2.31.1
>