linux-kernel - Re: [PATCH 3/8] gpio: zynq: Shift zynq_gpio_init() to subsys

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Date:   Mon, 14 Aug 2017 16:15:01 +0200
From:   Michal Simek <michal.simek@...inx.com>
To:     Linus Walleij <linus.walleij@...aro.org>,
        Michal Simek <michal.simek@...inx.com>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "monstr@...str.eu" <monstr@...str.eu>,
        Nava kishore Manne <nava.manne@...inx.com>,
        Sören Brinkmann <soren.brinkmann@...inx.com>,
        Steffen Trumtrar <s.trumtrar@...gutronix.de>,
        Peter Crosthwaite <peter.crosthwaite@...inx.com>,
        "linux-gpio@...r.kernel.org" <linux-gpio@...r.kernel.org>,
        Rob Herring <robherring2@...il.com>,
        Josh Cartwright <josh.cartwright@...com>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH 3/8] gpio: zynq: Shift zynq_gpio_init() to subsys_initcall
 level

On 14.8.2017 15:55, Linus Walleij wrote:
> On Mon, Aug 7, 2017 at 1:01 PM, Michal Simek <michal.simek@...inx.com> wrote:
> 
>> From: Nava kishore Manne <nava.manne@...inx.com>
>>
>> In general situation on-SoC GPIO controller drivers should be probed
>> after pinctrl/pinmux controller driver, because on-SoC GPIOs utilize a
>> pin/pad as a resource provided and controlled by pinctrl subsystem.
>>
>>   GPIO must come after pinctrl as gpios may need to mux pins....etc
>>
>> Looking at Xilinx SoC series pinctrl drivers, zynq*_pinctrl_init()
>> functions are called at arch_initcall init levels,
>> so the change of initcall level for gpio-zynq driver from
>> postcore_initcall to subsys_initcall level is sufficient. Also note
>> that the most of GPIO controller drivers settled at subsys_initcall
>> level.
>>
>> If pinctrl subsystem manages pads with GPIO functions, the change is
>> needed to avoid unwanted driver probe deferrals during kernel boot.
>>
>> Signed-off-by: Nava kishore Manne <navam@...inx.com>
>> Signed-off-by: Michal Simek <michal.simek@...inx.com>
> 
> Can't you just move it all the way to device_initcall and
> simply use the standard module init macros?
> builtin_platform_driver(), module_platform_driver()?

When I grep the kernel I see this

[linux](master)$ git grep "^core_initcall" drivers/gpio/ | wc -l
1
[linux](master)$ git grep "^postcore_initcall" drivers/gpio/ | wc -l
12
[linux](master)$ git grep "^arch_initcall" drivers/gpio/ | wc -l
2
[linux](master)$ git grep "^subsys_initcall" drivers/gpio/ | wc -l
33
[linux](master)$ git grep "^device_initcall" drivers/gpio/ | wc -l
4


[linux](master)$ git grep "^core_initcall" drivers/pinctrl/ | wc -l
6
[linux](master)$ git grep "^postcore_initcall" drivers/pinctrl/ | wc -l
7
[linux](master)$ git grep "^arch_initcall" drivers/pinctrl/ | wc -l
62
[linux](master)$ git grep "^subsys_initcall" drivers/pinctrl/ | wc -l
12
[linux](master)$ git grep "^device_initcall" drivers/pinctrl/ | wc -l
0

Majority of gpio drivers are in subsys_initcall and pinctrl in
arch_initcall. It doesn't mean that I have strong opinion about doing
this change. I have also read internal tracking system and it is not
fully clear if this is fixing any issue rather than removing on
deferring probe message.

Nava: Do you have any comment?

Thanks,
Michal