linux-kernel - Re: [PATCH 2/2] ARM: imx: src: support vf610 system reset controller

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Message-ID: <6341b31998ff843d236bc2a3e34537b0@agner.ch>
Date:	Fri, 28 Nov 2014 23:09:09 +0100
From:	Stefan Agner <stefan@...er.ch>
To:	Arnd Bergmann <arnd@...db.de>
Cc:	linux-arm-kernel@...ts.infradead.org, shawn.guo@...aro.org,
	kernel@...gutronix.de, linux@...ck-us.net,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] ARM: imx: src: support vf610 system reset controller

On 2014-11-28 22:24, Arnd Bergmann wrote:
> On Friday 28 November 2014 22:02:01 Stefan Agner wrote:
>> On 2014-11-28 17:49, Arnd Bergmann wrote:
>> > On Friday 28 November 2014 17:43:35 Stefan Agner wrote:
>> >> Support Vybrid SoC's system reset controller (SRC). Currently we
>> >> don't register a reset controller but only support the imx_cpu_jump
>> >> and imx_cpu_arg functions.
>> >>
>> >> Signed-off-by: Stefan Agner <stefan@...er.ch>
>> >
>> > I think this should be a platform driver in drivers/power/reset.
>>
>> Yeah, I thought that too, see my cover letter. The problem is, in that
>> module are also some register which are of interest when implementing
>> suspend/resume support (see cover letter too). However, we could also
>> just make a dt entry for that reset register only, and create another dt
>> entry for the other registers.
> 
> Don't make a node with just one register, in this case, a syscon device
> would be best.

Syscon seems like a match here. Was not aware of that, thx!

> 
>> > If the SRC is also capable of resetting individual blocks instead of just
>> > the entire machine, it would be a reset driver in drivers/reset instead.
>>
>> Beside the system reset, there is only a mask functionality for the
>> watchdogs (there are two watchdogs, one for Cortex-A5 and one for the
>> M4). This makes the SRC module in the Vybrid a bit different then what
>> is available on other i.MX SoC's...
> 
> If you already have the watchdog registers in there and want to have
> a watchdog driver too, the easiest way would be to register the reboot
> handler from the watchdog driver.

Hm, not sure we speak about the same here. The SRC module has two
(multi-)bit fields to mask the watchdog reset event for each watchdog.
Beside that, there are two full watchdog register maps, which are in
different areas. There is already a driver for this watchdogs. I'm not
sure what the idea behind this is exactly, I guess it would easily allow
to (temporary) mask the other CPU's watchdog. However, I don't think we
need that functionality, so I don't care about that right now.

There is also a restart handler in the watchdog driver, but I prefer to
use the reset capabilities of the SRC since it has immediate effect. 

Lets get to the big picture again: I could register the whole SRC
register map as a syscon device and then access the registers from my
suspend/resume implementation later on. And similar in the restart
driver, I would use syscon_regmap_lookup_by_compatible to check if it
contains the vf610-src compatible string and register the restart
driver/handler if available.

--
Stefan

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