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

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Date:	Sun, 30 Nov 2014 12:54:43 +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 Saturday 29 November 2014 01:15:57 Stefan Agner wrote:
> On 2014-11-28 23:22, Arnd Bergmann wrote:
> > 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.
> 
> One thing which came into my mind regarding suspend: I might need to
> access the registers from assembler (in SRAM), can I do that through
> syscon/regmap? I had a quick look, but I don't found a way to get back
> the mapped IO base address.. By good reasons, of course, for most
> applications. But in my case, afaik I have no other choice.

Yes, I can see that being a problem. What register specifically do
you need to access from code running in SRAM?

	Arnd
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