linux-kernel - Re: [RFC][PATCH] driver core: Extend returning EPROBE_DEFER for two minutes after late

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Date:   Thu, 13 Feb 2020 19:51:18 -0600
From:   Rob Herring <robh@...nel.org>
To:     John Stultz <john.stultz@...aro.org>
Cc:     lkml <linux-kernel@...r.kernel.org>,
        Alexander Graf <agraf@...e.de>,
        "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>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "open list:THERMAL" <linux-pm@...r.kernel.org>
Subject: Re: [RFC][PATCH] driver core: Extend returning EPROBE_DEFER for two
 minutes after late_initcall

On Thu, Feb 13, 2020 at 6:44 PM John Stultz <john.stultz@...aro.org> wrote:
>
> Due to commit e01afc3250255 ("PM / Domains: Stop deferring probe
> at the end of initcall"), along with commit 25b4e70dcce9
> ("driver core: allow stopping deferred probe after init") after
> late_initcall, drivers will stop getting EPROBE_DEFER, and
> instead see an error causing the driver to fail to load.
>
> That change causes trouble when trying to use many clk drivers
> as modules, as the clk modules may not load until much later
> after init has started. If a dependent driver loads and gets an
> error instead of EPROBE_DEFER, it won't try to reload later when
> the dependency is met, and will thus fail to load.
>
> Instead of reverting that patch, this patch tries to extend the
> time that EPROBE_DEFER is retruned by two minutes, to (hopefully)
> ensure that everything has had a chance to load.

I think regulators already has some delay like this. We should use the
same timeouts.

We also have the 'deferred_probe_timeout' cmdline option. It's deemed
a debug option currently, but we could change that and change the
default.

> Specifically, on db845c, this change allows us to set
> SDM_GPUCC_845, QCOM_CLK_RPMH and COMMON_CLK_QCOM as modules and
> get a working system, where as without it the display will fail
> to load.
>
> Cc: Alexander Graf <agraf@...e.de>
> 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: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
> Cc: linux-pm@...r.kernel.org
> Fixes: e01afc3250255 ("PM / Domains: Stop deferring probe at the end of initcall")
> Fixes: 25b4e70dcce9 ("driver core: allow stopping deferred probe after init")

We can debate the design, but those work as designed. So Fixes?

> Signed-off-by: John Stultz <john.stultz@...aro.org>
> ---
>  drivers/base/dd.c | 8 +++++++-
>  1 file changed, 7 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/base/dd.c b/drivers/base/dd.c
> index b25bcab2a26b..35ebae8b65be 100644
> --- a/drivers/base/dd.c
> +++ b/drivers/base/dd.c
> @@ -311,6 +311,12 @@ static void deferred_probe_timeout_work_func(struct work_struct *work)
>  }
>  static DECLARE_DELAYED_WORK(deferred_probe_timeout_work, deferred_probe_timeout_work_func);
>
> +static void deferred_initcall_done_work_func(struct work_struct *work)
> +{
> +       initcalls_done = true;
> +}
> +static DECLARE_DELAYED_WORK(deferred_initcall_done_work, deferred_initcall_done_work_func);
> +
>  /**
>   * deferred_probe_initcall() - Enable probing of deferred devices
>   *
> @@ -327,7 +333,7 @@ static int deferred_probe_initcall(void)
>         driver_deferred_probe_trigger();
>         /* Sort as many dependencies as possible before exiting initcalls */
>         flush_work(&deferred_probe_work);
> -       initcalls_done = true;
> +       schedule_delayed_work(&deferred_initcall_done_work, 120 * HZ);
>
>         /*
>          * Trigger deferred probe again, this time we won't defer anything
> --
> 2.17.1
>