linux-kernel - Re: [RFC][PATCH] pinctrl: Rework driver_deferred_probe_check_state() evaluation since default timeout has changed

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Date:   Fri, 28 Aug 2020 14:01:54 +0200
From:   Thierry Reding <treding@...dia.com>
To:     John Stultz <john.stultz@...aro.org>
CC:     lkml <linux-kernel@...r.kernel.org>, <linux-pm@...r.kernel.org>,
        "Greg Kroah-Hartman" <gregkh@...uxfoundation.org>,
        Linus Walleij <linus.walleij@...aro.org>,
        Mark Brown <broonie@...nel.org>,
        Liam Girdwood <lgirdwood@...il.com>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Saravana Kannan <saravanak@...gle.com>,
        Todd Kjos <tkjos@...gle.com>,
        "Len Brown" <len.brown@...el.com>, Pavel Machek <pavel@....cz>,
        Ulf Hansson <ulf.hansson@...aro.org>,
        Kevin Hilman <khilman@...nel.org>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Rob Herring <robh@...nel.org>
Subject: Re: [RFC][PATCH] pinctrl: Rework driver_deferred_probe_check_state()
 evaluation since default timeout has changed

On Sat, Aug 08, 2020 at 04:35:12AM +0000, John Stultz wrote:
> In commit bec6c0ecb243 ("pinctrl: Remove use of
> driver_deferred_probe_check_state_continue()"), we removed the
> use of driver_deferred_probe_check_state_continue() which
> effectively never returned -ETIMED_OUT, with the
> driver_deferred_probe_check_state() function that had been
> reworked to properly return ETIMED_OUT when the deferred probe
> timeout expired. Along with that change, we set the default
> timeout to 30 seconds.
> 
> However, since moving the timeout to 30 seconds caused some
> issues for some users with optional dt links, we set the
> default timeout back to zero - see commit ce68929f07de ("driver
> core: Revert default driver_deferred_probe_timeout value to 0")
> 
> This in essence changed the behavior of the pinctrl's usage
> of driver_deferred_probe_check_state(), as it now would return
> ETIMED_OUT by default. Thierry reported this caused problems with
> resume on tegra platforms.
> 
> Thus this patch tweaks the pinctrl logic so that it behaves as
> before. If modules are enabled, we'll only return EPROBE_DEFERRED
> while we're missing drivers linked in the DT.
> 
> Cc: linux-pm@...r.kernel.org
> Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
> Cc: Linus Walleij <linus.walleij@...aro.org>
> Cc: Thierry Reding <treding@...dia.com>
> Cc: Mark Brown <broonie@...nel.org>
> Cc: Liam Girdwood <lgirdwood@...il.com>
> Cc: Bjorn Andersson <bjorn.andersson@...aro.org>
> Cc: Saravana Kannan <saravanak@...gle.com>
> Cc: Todd Kjos <tkjos@...gle.com>
> Cc: Len Brown <len.brown@...el.com>
> Cc: Pavel Machek <pavel@....cz>
> Cc: Ulf Hansson <ulf.hansson@...aro.org>
> Cc: Kevin Hilman <khilman@...nel.org>
> Cc: "Rafael J. Wysocki" <rjw@...ysocki.net>
> Cc: Rob Herring <robh@...nel.org>
> Fixes: bec6c0ecb243 ("pinctrl: Remove use of driver_deferred_probe_check_state_continue()")
> Fixes: ce68929f07de ("driver core: Revert default driver_deferred_probe_timeout value to 0")
> Reported-by: Thierry Reding <thierry.reding@...il.com>
> Signed-off-by: John Stultz <john.stultz@...aro.org>
> ---
>  drivers/pinctrl/devicetree.c | 5 ++---
>  1 file changed, 2 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/pinctrl/devicetree.c b/drivers/pinctrl/devicetree.c
> index c6fe7d64c913..09ddf567ccb4 100644
> --- a/drivers/pinctrl/devicetree.c
> +++ b/drivers/pinctrl/devicetree.c
> @@ -129,9 +129,8 @@ static int dt_to_map_one_config(struct pinctrl *p,
>  		if (!np_pctldev || of_node_is_root(np_pctldev)) {
>  			of_node_put(np_pctldev);
>  			ret = driver_deferred_probe_check_state(p->dev);
> -			/* keep deferring if modules are enabled unless we've timed out */
> -			if (IS_ENABLED(CONFIG_MODULES) && !allow_default &&
> -			    (ret == -ENODEV))
> +			/* keep deferring if modules are enabled */
> +			if (IS_ENABLED(CONFIG_MODULES) && !allow_default)
>  				ret = -EPROBE_DEFER;
>  			return ret;
>  		}

I posted almost exactly the same patch a couple of days ago since I
hadn't noticed this:

	https://patchwork.ozlabs.org/project/linux-gpio/patch/20200825143348.1358679-1-thierry.reding@gmail.com/

I like that slightly better because it keeps the "ret < 0" condition,
which I think is perhaps a bit more future-proof. Thinking about it, I'm
not sure your version above is entirely correct. For example if the call
to driver_deferred_probe_check_state() were to ever return 0, we might
still be returning -EPROBE_DEFER here.

That's not something that happens currently, but I suspect that these
implications will be easy to overlook.

Actually... I think it might be best to just bring back (albeit perhaps
in a modified form) driver_deferred_probe_check_state_continue() because
we're now basically doing exactly what that was supposed to do: special-
casing the case where we do want to continue returning -EPROBE_DEFER in
some special cases.

Thierry

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