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Message-ID: <CAMuHMdWYpxiWvmo+ER5L6853COsx9OQzkz=uwmhDjtM6_F8+Aw@mail.gmail.com>
Date: Mon, 22 Jun 2015 12:25:31 +0200
From: Geert Uytterhoeven <geert@...ux-m68k.org>
To: Alexandre Courbot <gnurou@...il.com>
Cc: Geert Uytterhoeven <geert+renesas@...der.be>,
Linus Walleij <linus.walleij@...aro.org>,
Benoit Parrot <bparrot@...com>,
Maxime Ripard <maxime.ripard@...e-electrons.com>,
Boris Brezillon <boris.brezillon@...e-electrons.com>,
"linux-gpio@...r.kernel.org" <linux-gpio@...r.kernel.org>,
Linux-SH <linux-sh@...r.kernel.org>,
Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
Laurent Pinchart <laurent.pinchart+renesas@...asonboard.com>
Subject: Re: [PATCH] [RFC] gpio: Retry deferred GPIO hogging on pin range change
On Sun, Jun 21, 2015 at 10:52 AM, Geert Uytterhoeven
<geert@...ux-m68k.org> wrote:
> On Sun, Jun 21, 2015 at 9:21 AM, Alexandre Courbot <gnurou@...il.com> wrote:
>> On Tue, Jun 16, 2015 at 9:36 PM, Geert Uytterhoeven
>> <geert+renesas@...der.be> wrote:
>>> If a GPIO driver uses gpiochip_add_pin_range() (which is usually the
>>> case for GPIO/PFC combos), the GPIO hogging mechanism configured from DT
>>> doesn't work:
>>>
>>> requesting hog GPIO lcd0 (chip r8a7740_pfc, offset 176) failed
>>>
>>> The actual error code is -517 == -EPROBE_DEFER.
>>>
>>> The problem is that PFC+GPIO registration is handled in multiple steps:
>>> 1. pinctrl_register(),
>>> 2. gpiochip_add(),
>>> 3. gpiochip_add_pin_range().
>>>
>>> Configuration of the hogs is handled in gpiochip_add():
>>>
>>> gpiochip_add
>>> of_gpiochip_add
>>> of_gpiochip_scan_hogs
>>> gpiod_hog
>>> gpiochip_request_own_desc
>>> __gpiod_request
>>> chip->request
>>> pinctrl_request_gpio
>>> pinctrl_get_device_gpio_range
>>>
>>> However, at this point the GPIO controller hasn't been added to
>>> pinctrldev_list yet, so the range can't be found, and the operation fails
>>> with -EPROBE_DEFER.
>>>
>>> - Exchanging the order of the calls to gpiochip_add() and
>>> gpiochip_add_pin_range() is not an option, as the latter depends on
>>> initialization done by the former.
>>> - Just moving the call of of_gpiochip_scan_hogs() from gpiochip_add()
>>> to gpiochip_add_pin_range() is also not an option, as the latter is
>>> optional, and thus not used by all drivers.
>>>
>>> Hence if of_gpiochip_scan_hogs() fails with -EPROBE_DEFER, call it
>>> again every time the pin range is changed, until it succeeded.
>>>
>>> Signed-off-by: Geert Uytterhoeven <geert+renesas@...der.be>
>>> ---
>>> Questions:
>>> - Is there a better solution to handle this?
>>
>> I do not understand the issue well enough to propose a better
>> solution, but I really hope there is one. This turns GPIO into a
>> slightly bigger yarn mess that what it already is and does not help
>> understanding how probing is performed. Yielding in the middle of
>> adding hogs and re-trying later sounds like a recipe for issues like
>> hogs being added several times.
>>
>> So I am not really fond of this, to be honest. The GPIO hogging
>> mechanism is still quite new, so there is certainly a way to fix such
>> issues by addressing the fundamental cause instead of duct taping it?
>
> Sure, I'm all for fixing this properly, hence the "RFC" and my questions.
>
> I also don't understand how this interacts with non-PFC drivers calling
> gpiochip_add_pin_range():
> - gpio-em, but only for legacy platform devices, which are no longer used
> (I will remove the legacy support),
> - gpio-rcar, but only for legacy platform devices, which is used on R-Car
> Gen1 only until -legacy is removed,
> - gpiolib-of, which handles this for the bulk of modern GPIO drivers using
> the "gpio-ranges" and "gpio-ranges-group-names" properties in DT.
>
> When I noticed the failure on r8a7740/armadillo (sh-pfc provides both pfc
> and gpio), I tried GPIO hogging on r8a7791/koelsch (sh-pfc provides pfc
> only, gpio-rcar provides gpio, "gpio-ranges" is in DT), and there it worked
> fine without my patch.
"gpio-ranges" and gpiochip_add_pin_range() turned out to be the solution
to the problem: on DT platforms, parsing "gpio-ranges" is doing from
of_gpiochip_add(), which is called from gpiochip_add().
Hence the ranges are set up from DT just before the hogs are handled:
void of_gpiochip_add(struct gpio_chip *chip)
{
...
of_gpiochip_add_pin_range(chip);
...
of_gpiochip_scan_hogs(chip);
}
Sticking a "gpio-ranges" in arch/arm/boot/dts/r8a7740.dtsi:
@@ -288,12 +288,13 @@
pfc: pfc@...50000 {
compatible = "renesas,pfc-r8a7740";
reg = <0xe6050000 0x8000>,
<0xe605800c 0x20>;
gpio-controller;
#gpio-cells = <2>;
+ gpio-ranges = <&pfc 0 0 212>;
interrupts-extended =
<&irqpin0 0 0>, <&irqpin0 1 0>, <&irqpin0 2
0>, <&irqpin0 3 0>,
<&irqpin0 4 0>, <&irqpin0 5 0>, <&irqpin0 6
0>, <&irqpin0 7 0>,
<&irqpin1 0 0>, <&irqpin1 1 0>, <&irqpin1 2
0>, <&irqpin1 3 0>,
<&irqpin1 4 0>, <&irqpin1 5 0>, <&irqpin1 6
0>, <&irqpin1 7 0>,
<&irqpin2 0 0>, <&irqpin2 1 0>, <&irqpin2 2
0>, <&irqpin2 3 0>,
solved the problem for me.
Note that "&pfc" is a reference to the gpio device node itself, as it provides
both GPIO and PFC functionalities.
After that, the calls to gpiochip_add_pin_range() in
drivers/pinctrl/sh-pfc/gpio.c
can be removed, at least for the ARM multi-platform case where GPIO is
instantiated from DT (_and_ "gpio-ranges" is present --- I don't think we have
to care about DT backwards compatibility for sh73a0/r8a73a4/r8a7740).
Does this makes sense?
I couldn't find any other in-tree DTS that has a gpio-controller with a
gpio-ranges pointing to itself. All other GPIO+PFC combos lack such properties,
and thus probably won't work with DT gpio-hogs.
Thanks for your comments!
Gr{oetje,eeting}s,
Geert
--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org
In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
-- Linus Torvalds
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