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

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Message-ID: <18555848.LVhqYu0kXL@wuerfel>
Date:	Fri, 28 Nov 2014 23:22:57 +0100
From:	Arnd Bergmann <arnd@...db.de>
To:	Stefan Agner <stefan@...er.ch>
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 Friday 28 November 2014 23:09:09 Stefan Agner wrote:
> On 2014-11-28 22:24, Arnd Bergmann wrote:
> > On Friday 28 November 2014 22:02:01 Stefan Agner wrote:
> > 
> >> > 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.

Ok, I see, thanks for the clarification!

> 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.

Correct, and also in the watchdog driver, I guess.

Instead of syscon_regmap_lookup_by_compatible, please use
syscon_regmap_lookup_by_phandle and put the link to the syscon
device into the device accessing it.

Also, see if you can use or extend drivers/power/reset/syscon-reboot.c
for your use case.

	Arnd
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