linux-kernel - Re: [PATCH 3/7] reset: lpc18xx: use devm_reset_controller

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Message-ID: <CAK7LNAQga-dCmAWevKMQx2DBzGim8DmNyeCxj4n5q-SjEapd+Q@mail.gmail.com>
Date:	Tue, 3 May 2016 19:25:39 +0900
From:	Masahiro Yamada <yamada.masahiro@...ionext.com>
To:	Philipp Zabel <p.zabel@...gutronix.de>
Cc:	Joachim Eastwood <manabian@...il.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH 3/7] reset: lpc18xx: use devm_reset_controller_register()

Hi Philipp,

2016-05-03 18:05 GMT+09:00 Philipp Zabel <p.zabel@...gutronix.de>:
> Am Dienstag, den 03.05.2016, 00:52 +0900 schrieb Masahiro Yamada:
>> 2016-05-02 17:26 GMT+09:00 Philipp Zabel <p.zabel@...gutronix.de>:
>> > Am Sonntag, den 01.05.2016, 19:36 +0900 schrieb Masahiro Yamada:
>> >> Use devm_reset_controller_register() for the reset controller
>> >> registration and remove the unregister call from the .remove callback.
>> >>
>> >> Signed-off-by: Masahiro Yamada <yamada.masahiro@...ionext.com>
>> >> ---
>> >>
>> >>  drivers/reset/reset-lpc18xx.c | 4 +---
>> >>  1 file changed, 1 insertion(+), 3 deletions(-)
>> >>
>> >> diff --git a/drivers/reset/reset-lpc18xx.c b/drivers/reset/reset-lpc18xx.c
>> >> index 3b8a4f5..dd4f27e 100644
>> >> --- a/drivers/reset/reset-lpc18xx.c
>> >> +++ b/drivers/reset/reset-lpc18xx.c
>> >> @@ -199,7 +199,7 @@ static int lpc18xx_rgu_probe(struct platform_device *pdev)
>> >>
>> >>       platform_set_drvdata(pdev, rc);
>> >>
>> >> -     ret = reset_controller_register(&rc->rcdev);
>> >> +     ret = devm_reset_controller_register(&pdev->dev, &rc->rcdev);
>> >>       if (ret) {
>> >>               dev_err(&pdev->dev, "unable to register device\n");
>> >>               goto dis_clks;
>> >> @@ -229,8 +229,6 @@ static int lpc18xx_rgu_remove(struct platform_device *pdev)
>> >>       if (ret)
>> >>               dev_warn(&pdev->dev, "failed to unregister restart handler\n");
>> >>
>> >> -     reset_controller_unregister(&rc->rcdev);
>> >> -
>> >>       clk_disable_unprepare(rc->clk_delay);
>> >>       clk_disable_unprepare(rc->clk_reg);
>> >>
>> >
>> > Hmm, would this patch theoretically allow a window between the calls to
>> > clk_disable_unprepare(clk_reg) and devm_reset_controller_release() where
>> > reset_control_get() + reset_control_(de)assert() would access unclocked
>> > registers?
>>
>> This is not clear to me.
>>
>> Why reset_control_get() + reset_control_(de)assert() would happen here?
>
> I suppose on a non-SMP device, without parallel probing this can't
> really happen in practice.
> It still seems weird that suddenly we disable the clocks before
> unregistering the reset controller instead of afterwards.
>

I still do not understand what you mean.

This patch moves the reset_controller_unregister() call
after clk_disable_unprepare().


But, reset_controller_unregister() is just a manipulation of a liked list.
It does not trigger any hardware access.

Am I wrong?

void reset_controller_unregister(struct reset_controller_dev *rcdev)
{
        mutex_lock(&reset_controller_list_mutex);
        list_del(&rcdev->list);
        mutex_unlock(&reset_controller_list_mutex);
}



-- 
Best Regards
Masahiro Yamada