Date:   Sat, 22 Jun 2019 11:01:44 +0200
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     Thierry Reding <thierry.reding@...il.com>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Rafael J . Wysocki" <rafael@...nel.org>,
        Linus Walleij <linus.walleij@...aro.org>,
        Rob Herring <robh@...nel.org>, linux-gpio@...r.kernel.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3] driver: core: Allow subsystems to continue deferring probe

On Fri, Jun 21, 2019 at 5:17 PM Thierry Reding <thierry.reding@...il.com> wrote:
>
> From: Thierry Reding <treding@...dia.com>
>
> Some subsystems, such as pinctrl, allow continuing to defer probe
> indefinitely. This is useful for devices that depend on resources
> provided by devices that are only probed after the init stage.
>
> One example of this can be seen on Tegra, where the DPAUX hardware
> contains pinmuxing controls for pins that it shares with an I2C
> controller. The I2C controller is typically used for communication
> with a monitor over HDMI (DDC). However, other instances of the I2C
> controller are used to access system critical components, such as a
> PMIC. The I2C controller driver will therefore usually be a builtin
> driver, whereas the DPAUX driver is part of the display driver that
> is loaded from a module to avoid bloating the kernel image with all
> of the DRM/KMS subsystem.
>
> In this particular case the pins used by this I2C/DDC controller
> become accessible very late in the boot process. However, since the
> controller is only used in conjunction with display, that's not an
> issue.
>
> Unfortunately the driver core currently outputs a warning message
> when a device fails to get the pinctrl before the end of the init
> stage. That can be confusing for the user because it may sound like
> an unwanted error occurred, whereas it's really an expected and
> harmless situation.
>
> In order to eliminate this warning, this patch allows callers of the
> driver_deferred_probe_check_state() helper to specify that they want
> to continue deferring probe, regardless of whether we're past the
> init stage or not. All of the callers of that function are updated
> for the new signature, but only the pinctrl subsystem passes a true
> value in the new persist parameter if appropriate.
>
> Signed-off-by: Thierry Reding <treding@...dia.com>

Overall

Reviewed-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>

with one nit below.

> ---
> Changes in v3:
> - add new function rather than extend the existing function with flags
>
> Changes in v2:
> - pass persist flag via flags parameter to make the function call easier
>   to understand
>
>  drivers/base/dd.c            | 55 ++++++++++++++++++++++++++++++------
>  drivers/pinctrl/devicetree.c |  7 ++---
>  include/linux/device.h       |  1 +
>  3 files changed, 51 insertions(+), 12 deletions(-)
>
> diff --git a/drivers/base/dd.c b/drivers/base/dd.c
> index 0df9b4461766..994a90747420 100644
> --- a/drivers/base/dd.c
> +++ b/drivers/base/dd.c
> @@ -235,6 +235,19 @@ static int __init deferred_probe_timeout_setup(char *str)
>  }
>  __setup("deferred_probe_timeout=", deferred_probe_timeout_setup);
>
> +static int __driver_deferred_probe_check_state(struct device *dev)
> +{
> +       if (!initcalls_done)
> +               return -EPROBE_DEFER;
> +
> +       if (!deferred_probe_timeout) {
> +               dev_WARN(dev, "deferred probe timeout, ignoring dependency");
> +               return -ETIMEDOUT;
> +       }
> +
> +       return 0;
> +}
> +
>  /**
>   * driver_deferred_probe_check_state() - Check deferred probe state
>   * @dev: device to check
> @@ -248,14 +261,40 @@ __setup("deferred_probe_timeout=", deferred_probe_timeout_setup);
>   */
>  int driver_deferred_probe_check_state(struct device *dev)
>  {
> -       if (initcalls_done) {
> -               if (!deferred_probe_timeout) {
> -                       dev_WARN(dev, "deferred probe timeout, ignoring dependency");
> -                       return -ETIMEDOUT;
> -               }
> -               dev_warn(dev, "ignoring dependency for device, assuming no driver");
> -               return -ENODEV;
> -       }
> +       int ret;
> +
> +       ret = __driver_deferred_probe_check_state(dev);
> +       if (ret < 0)

The function returning this valie doesn't return positive numbers, so
it "if (ret)" would be sufficient here (and below).

> +               return ret;
> +
> +       dev_warn(dev, "ignoring dependency for device, assuming no driver");
> +
> +       return -ENODEV;
> +}
> +
> +/**
> + * driver_deferred_probe_check_state_continue() - check deferred probe state
> + * @dev: device to check
> + *
> + * Returns -ETIMEDOUT if deferred probe debug timeout has expired, or
> + * -EPROBE_DEFER otherwise.
> + *
> + * Drivers or subsystems can opt-in to calling this function instead of
> + * directly returning -EPROBE_DEFER.
> + *
> + * This is similar to driver_deferred_probe_check_state(), but it allows the
> + * subsystem to keep deferring probe after built-in drivers have had a chance
> + * to probe. One scenario where that is useful is if built-in drivers rely on
> + * resources that are provided by modular drivers.
> + */
> +int driver_deferred_probe_check_state_continue(struct device *dev)
> +{
> +       int ret;
> +
> +       ret = __driver_deferred_probe_check_state(dev);
> +       if (ret < 0)
> +               return ret;
> +
>         return -EPROBE_DEFER;
>  }

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