linux-kernel - Re: [PATCH v4 1/6] driver core: Fix driver_deferred_probe_check

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Date:   Thu, 20 Feb 2020 11:28:30 +0100
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     John Stultz <john.stultz@...aro.org>
Cc:     lkml <linux-kernel@...r.kernel.org>, Rob Herring <robh@...nel.org>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Kevin Hilman <khilman@...nel.org>,
        Ulf Hansson <ulf.hansson@...aro.org>,
        Pavel Machek <pavel@....cz>, Len Brown <len.brown@...el.com>,
        Todd Kjos <tkjos@...gle.com>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Liam Girdwood <lgirdwood@...il.com>,
        Mark Brown <broonie@...nel.org>,
        Thierry Reding <treding@...dia.com>,
        Linus Walleij <linus.walleij@...aro.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Linux PM <linux-pm@...r.kernel.org>
Subject: Re: [PATCH v4 1/6] driver core: Fix driver_deferred_probe_check_state()
 logic

On Thu, Feb 20, 2020 at 6:05 AM John Stultz <john.stultz@...aro.org> wrote:
>
> driver_deferred_probe_check_state() has some uninituitive behavior.
>
> * From boot to late_initcall, it returns -EPROBE_DEFER
>
> * From late_initcall to the deferred_probe_timeout (if set)
>   it returns -ENODEV
>
> * If the deferred_probe_timeout it set, after it fires, it
>   returns -ETIMEDOUT
>
> This is a bit confusing, as its useful to have the function
> return -EPROBE_DEFER while the timeout is still running. This
> behavior has resulted in the somwhat duplicative
> driver_deferred_probe_check_state_continue() function being
> added.
>
> Thus this patch tries to improve the logic, so that it behaves
> as such:
>
> * If deferred_probe_timeout is set, it returns -EPROBE_DEFER
>   until the timeout, afterwhich it returns -ETIMEDOUT.
>
> * If deferred_probe_timeout is not set (-1), it returns
>   -EPROBE_DEFER until late_initcall, after which it returns
>
> This will make the deferred_probe_timeout value much more
> functional, and will allow us to consolidate the
> driver_deferred_probe_check_state() and
> driver_deferred_probe_check_state_continue() logic in a later
> patch.
>
> Cc: Rob Herring <robh@...nel.org>
> Cc: "Rafael J. Wysocki" <rjw@...ysocki.net>
> Cc: Kevin Hilman <khilman@...nel.org>
> Cc: Ulf Hansson <ulf.hansson@...aro.org>
> Cc: Pavel Machek <pavel@....cz>
> Cc: Len Brown <len.brown@...el.com>
> Cc: Todd Kjos <tkjos@...gle.com>
> Cc: Bjorn Andersson <bjorn.andersson@...aro.org>
> Cc: Liam Girdwood <lgirdwood@...il.com>
> Cc: Mark Brown <broonie@...nel.org>
> Cc: Thierry Reding <treding@...dia.com>
> Cc: Linus Walleij <linus.walleij@...aro.org>
> Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
> Cc: linux-pm@...r.kernel.org
> Signed-off-by: John Stultz <john.stultz@...aro.org>
> Change-Id: I8349b7a403ce8cbce485ea0a0a5512fddffb635c
> ---
> v4:
> * Simplified logic suggested by Andy Shevchenko
> * Clarified commit message to focus on logic change
> ---
>  drivers/base/dd.c | 10 ++++++----
>  1 file changed, 6 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/base/dd.c b/drivers/base/dd.c
> index b25bcab2a26b..bb383dca39c1 100644
> --- a/drivers/base/dd.c
> +++ b/drivers/base/dd.c
> @@ -237,7 +237,7 @@ __setup("deferred_probe_timeout=", deferred_probe_timeout_setup);
>
>  static int __driver_deferred_probe_check_state(struct device *dev)
>  {
> -       if (!initcalls_done)
> +       if (!initcalls_done || deferred_probe_timeout > 0)
>                 return -EPROBE_DEFER;

Makes sense to me.

>
>         if (!deferred_probe_timeout) {
> @@ -252,9 +252,11 @@ static int __driver_deferred_probe_check_state(struct device *dev)
>   * driver_deferred_probe_check_state() - Check deferred probe state
>   * @dev: device to check
>   *
> - * Returns -ENODEV if init is done and all built-in drivers have had a chance
> - * to probe (i.e. initcalls are done), -ETIMEDOUT if deferred probe debug
> - * timeout has expired, or -EPROBE_DEFER if none of those conditions are met.
> + * Returnes -EPROBE_DEFER if initcalls have not completed, or the deferred

s/Returnes/Returns/

And I would write

* Return:
* -EPROBE_DEFER if initcalls have not completed, or the deferred
*  probe timeout is set, but not expried.
* -ETIMEDOUT if the deferred probe timeout was set and has expired.
* -ENODEV if initcalls have completed and the deferred probe timeout
was not set.

> + * probe timeout is set, but not expried.
> + * Returns -ETIMEDOUT if the probe timeout was set and has expired.
> + * Returns -ENODEV if initcalls have completed and the deferred probe timeout
> + * was not set.
>   *
>   * Drivers or subsystems can opt-in to calling this function instead of directly
>   * returning -EPROBE_DEFER.
> --