linux-kernel - Re: [v5 3/5] drm/panel-simple: Support for delays between GPIO & regulator

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Message-ID: <CAD=FV=UncbMRcrJmMiCNT6YSoSGzENnmwfEBqmV2aEGXO5mA+Q@mail.gmail.com>
Date:   Wed, 2 Jun 2021 17:05:42 -0700
From:   Doug Anderson <dianders@...omium.org>
To:     Rajeev Nandan <rajeevny@...eaurora.org>
Cc:     dri-devel <dri-devel@...ts.freedesktop.org>,
        linux-arm-msm <linux-arm-msm@...r.kernel.org>,
        freedreno <freedreno@...ts.freedesktop.org>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>, LKML <linux-kernel@...r.kernel.org>,
        Thierry Reding <thierry.reding@...il.com>,
        Sam Ravnborg <sam@...nborg.org>,
        Rob Clark <robdclark@...il.com>, Lyude Paul <lyude@...hat.com>,
        Jani Nikula <jani.nikula@...el.com>,
        Rob Herring <robh@...nel.org>,
        Laurent Pinchart <laurent.pinchart@...asonboard.com>,
        Andrzej Hajda <a.hajda@...sung.com>,
        Daniel Thompson <daniel.thompson@...aro.org>,
        "Kristian H. Kristensen" <hoegsberg@...omium.org>,
        Abhinav Kumar <abhinavk@...eaurora.org>,
        Sean Paul <seanpaul@...omium.org>,
        Kalyan Thota <kalyan_t@...eaurora.org>,
        Krishna Manikandan <mkrishn@...eaurora.org>
Subject: Re: [v5 3/5] drm/panel-simple: Support for delays between GPIO & regulator

Hi,

On Sun, May 30, 2021 at 8:57 AM Rajeev Nandan <rajeevny@...eaurora.org> wrote:
>
> Some panels datasheets may specify a delay between the enable GPIO and
> the regulator. Support this in panel-simple.
>
> Signed-off-by: Rajeev Nandan <rajeevny@...eaurora.org>
> ---
>
> Changes in v4:
> - New
>
> Changes in v5:
> - Update description (Douglas)
> - Warn if "power_to_enable" or "disable_to_power_off" is non-zero and panel->enable_gpio
>   is NULL (Douglas)
>
>  drivers/gpu/drm/panel/panel-simple.c | 28 ++++++++++++++++++++++++++++
>  1 file changed, 28 insertions(+)
>
> diff --git a/drivers/gpu/drm/panel/panel-simple.c b/drivers/gpu/drm/panel/panel-simple.c
> index 047fad5..e3f5b7e 100644
> --- a/drivers/gpu/drm/panel/panel-simple.c
> +++ b/drivers/gpu/drm/panel/panel-simple.c
> @@ -133,6 +133,22 @@ struct panel_desc {
>                 unsigned int prepare_to_enable;
>
>                 /**
> +                * @delay.power_to_enable: Time for the power to enable the display on.
> +                *
> +                * The time (in milliseconds) to wait after powering up the display
> +                * before asserting its enable pin.
> +                */
> +               unsigned int power_to_enable;
> +
> +               /**
> +                * @delay.disable_to_power_off: Time for the disable to power the display off.
> +                *
> +                * The time (in milliseconds) to wait before powering off the display
> +                * after deasserting its enable pin.
> +                */
> +               unsigned int disable_to_power_off;
> +
> +               /**
>                  * @delay.enable: Time for the panel to display a valid frame.
>                  *
>                  * The time (in milliseconds) that it takes for the panel to
> @@ -347,6 +363,10 @@ static int panel_simple_suspend(struct device *dev)
>         struct panel_simple *p = dev_get_drvdata(dev);
>
>         gpiod_set_value_cansleep(p->enable_gpio, 0);
> +
> +       if (p->desc->delay.disable_to_power_off)
> +               msleep(p->desc->delay.disable_to_power_off);
> +
>         regulator_disable(p->supply);
>         p->unprepared_time = ktime_get();
>
> @@ -407,6 +427,9 @@ static int panel_simple_prepare_once(struct panel_simple *p)
>                 return err;
>         }
>
> +       if (p->desc->delay.power_to_enable)
> +               msleep(p->desc->delay.power_to_enable);
> +
>         gpiod_set_value_cansleep(p->enable_gpio, 1);
>
>         delay = p->desc->delay.prepare;
> @@ -782,6 +805,11 @@ static int panel_simple_probe(struct device *dev, const struct panel_desc *desc,
>                 break;
>         }
>
> +       if (!panel->enable_gpio && desc->delay.disable_to_power_off)
> +               dev_warn(dev, "Specify enable_gpio when using disable_to_power_off delay\n");
> +       if (!panel->enable_gpio && desc->delay.power_to_enable)
> +               dev_warn(dev, "Specify enable_gpio when using power_to_enable delay\n");

Last nit is that the warning messages could be a little confusing to
someone reading the logs. I guess the target audience of the error
message is probably someone doing bringup. That person specified a
panel in their device tree and maybe isn't even aware that they're
using "disable_to_power_off" or "power_to_enable". Maybe wording
instead:

Need a delay after disabling panel GPIO, but a GPIO wasn't provided.
Need a delay after enabling panel GPIO, but a GPIO wasn't provided.

That's definitely getting into nittiness, though and I wouldn't be
upset if the patch landed with the existing messages. Thus, with or
without the change to the error message:

Reviewed-by: Douglas Anderson <dianders@...omium.org>