linux-kernel - Re: [PATCH v8 07/16] drivers: reset: Add STM32 reset driver

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Message-ID: <CALszF6Bhc1MkDaqM3oJ93Rrxxbsss7=FA8WUpbtwmDERUdD0KA@mail.gmail.com>
Date:	Thu, 21 May 2015 21:57:56 +0200
From:	Maxime Coquelin <mcoquelin.stm32@...il.com>
To:	Andreas Färber <afaerber@...e.de>,
	Kamil Lulko <rev13@...pl>, Rob Herring <robh+dt@...nel.org>,
	Arnd Bergmann <arnd@...db.de>
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	"linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
	Linus Walleij <linus.walleij@...aro.org>,
	Will Deacon <will.deacon@....com>,
	Stefan Agner <stefan@...er.ch>,
	Nikolay Borisov <Nikolay.Borisov@....com>,
	Peter Meerwald <pmeerw@...erw.net>,
	Lee Jones <lee.jones@...aro.org>,
	Linux-Arch <linux-arch@...r.kernel.org>,
	Daniel Thompson <daniel.thompson@...aro.org>,
	Russell King <linux@....linux.org.uk>,
	Pawel Moll <pawel.moll@....com>,
	Jonathan Corbet <corbet@....net>, Jiri Slaby <jslaby@...e.cz>,
	Daniel Lezcano <daniel.lezcano@...aro.org>,
	Chanwoo Choi <cw00.choi@...sung.com>,
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	Geert Uytterhoeven <geert@...ux-m68k.org>,
	"linux-serial@...r.kernel.org" <linux-serial@...r.kernel.org>,
	Uwe Kleine-König 
	<u.kleine-koenig@...gutronix.de>,
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	Vladimir Zapolskiy <vladimir_zapolskiy@...tor.com>
Subject: Re: [PATCH v8 07/16] drivers: reset: Add STM32 reset driver

2015-05-21 19:58 GMT+02:00 Andreas Färber <afaerber@...e.de>:
> Am 21.05.2015 um 09:46 schrieb Maxime Coquelin:
>> 2015-05-21 1:45 GMT+02:00 Andreas Färber <afaerber@...e.de>:
>>> Am 09.05.2015 um 09:53 schrieb Maxime Coquelin:
>>>> +static const struct of_device_id stm32_reset_dt_ids[] = {
>>>> +      { .compatible = "st,stm32-rcc", },
>>>> +      { /* sentinel */ },
>>>> +};
>>>> +MODULE_DEVICE_TABLE(of, sstm32_reset_dt_ids);
>>>
>>> Typo.
>>
>> Indeed, thanks for pointing this out.
>>
>>>
>>> IIUC the timer depends on the reset controller, so it must be built in
>>> anyway, and that's what's enforced in the Makefile above. Drop the line?
>>>
>>
>> Agree it must be built-in.
>> I will fix that in next version.
>
> Actually, I've updated a timer implementation of mine to invoke a reset
> controller similar to how you do in the STM32 clocksource patch, but no
> reset controller is getting returned.
>
> It seems to me, you are working around that by simply ignoring the error
> in the timer code and not doing a reset then, so the STM32 timer does in
> fact _not_ depend on the reset controller? What happened to your efforts
> of making the reset controller usable for the timer? In my case, my
> timer is originally in reset state and needs to be deasserted, so I
> can't just ignore it.

Indeed, I made the reset optionnal in the clocksource patch since v3.
Rob and Arnd said a lot of platform relies on such things are done by
the bootloader [0].
I decided to deassert timers reset at bootloader stage, and make it
optionnal in clocksource driver.
I made it optionnal in case we decide one day to move reset
initialization before timer are initialized.

Note that for now, I still use your bootloader.
I have done the changes to reset the timers in the afboot-stm32.
That's the reason why I asked you under which licence it is delivered
few months ago.
I can share you the patch if you want, even if I understand it is more
about the concept that you are reluctant.

On my side, I plan to move to U-Boot soon, as Kamil Lulko added STM32
support in mainline [1].
In case of U-Boot, the timer reset should be de-asserted when jumping
into the Kernel, as Rob mentionned [0].

Kind regards,
Maxime

[0]: https://lkml.org/lkml/2015/3/10/737
[1]: http://u-boot.10912.n7.nabble.com/PATCH-v2-stm32f4-fix-serial-output-td212812.html
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