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

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Message-ID: <555E559F.8040403@suse.de>
Date:	Fri, 22 May 2015 00:01:03 +0200
From:	Andreas Färber <afaerber@...e.de>
To:	Maxime Coquelin <mcoquelin.stm32@...il.com>
CC:	Kamil Lulko <rev13@...pl>, Rob Herring <robh+dt@...nel.org>,
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Subject: Re: [PATCH v8 07/16] drivers: reset: Add STM32 reset driver

Am 21.05.2015 um 21:57 schrieb Maxime Coquelin:
> 2015-05-21 19:58 GMT+02:00 Andreas Färber <afaerber@...e.de>:
>> 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.

Sorry, too many mails... The stm32 one is GPL-2.0, as parts of it were
derived from a U-Boot fork. (Personally I prefer GPL-2.0+; fm4 and
xmc4000 are MIT/X11.)

> 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].

You're free to use any bootloader you like, but you will find it
difficult to build in USB etc. drivers given the sheer size of U-Boot.
That was my motivation for writing the tiny one. ;)

> In case of U-Boot, the timer reset should be de-asserted when jumping
> into the Kernel, as Rob mentionned [0].

Thanks, I've updated the xmc4000 one accordingly and can do the same for
stm32. But you are right that I consider that an ugly workaround,
although on the other hand my earlyprintk patches also depend on the
bootloader setting up GPIOs and UART.

Regards,
Andreas

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