linux-kernel - Re: [RFC PATCH] dt: describe base reset signal binding

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Date:	Wed, 31 Oct 2012 16:47:15 -0600
From:	Stephen Warren <swarren@...dotorg.org>
To:	Mike Turquette <mturquette@...com>
CC:	Rob Herring <rob.herring@...xeda.com>,
	Grant Likely <grant.likely@...retlab.ca>,
	"Rafael J. Wysocki" <rjw@...k.pl>,
	devicetree-discuss@...ts.ozlabs.org,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	Stephen Warren <swarren@...dia.com>
Subject: Re: [RFC PATCH] dt: describe base reset signal binding

On 10/31/2012 04:32 AM, Mike Turquette wrote:
> Quoting Stephen Warren (2012-10-30 11:02:05)
>> On 10/29/2012 12:32 PM, Mike Turquette wrote:
>>> Quoting Stephen Warren (2012-10-23 14:45:56)
>>>> What do people think of this? Does it sound like a good idea to go ahead
>>>> with a reset subsystem? Should we simply add a new API to the common clock
>>>> subsystem instead (and assume that reset and clock domains match 1:1).
>>>> Should this be implemented as part of the generic power management domains;
>>>> see include/linux/pm_domain.h instead?
>>>>
>>>
>>> Hi Stephen,
>>>
>>> I'm not sure a "reset subsystem" is necessary, but I also do not like
>>> using clocks as the keys for IP reset.
>>
>> I'm not sure what you're suggesting as an alternative to a reset
>> subsystem (or API if you want something that sounds smaller!) :-)
> 
> My point was that I do not know if a new subsystem is necessary or not.
> Your suggestion to "simply add a new API to the common clock subsystem"
> is an example of an alternative to a whole new subsystem.  However I
> instinctively feel that the clock api is not the right place for
> reseting devices.

driver/base/power is about the only related place I can think of given a
quick look. However, in a similar way to clocks, I don't think there's
necessarily a 1:1 relationship between power domains and reset domains
either, so driver/base/power doesn't feel like a good fit in just the
same way that drivers/clk doesn't.

I wonder if a drivers/base/reset/ or drivers/base/reset.c would be
appropriate?

>>> I think it is more common to map IPs to struct device, no?
>>
>> It is indeed probably common that there's a 1:1 mapping between IP
>> blocks and struct device. However, I'm sure there are plenty of
>> counter-examples; IP blocks with multiple reset domains (hence struct
>> devices that encompass multiple reset domains, or reset domains that
>> encompass multiple struct devices), just as there are many examples of
>> non-1:1 mappings between struct device and struct clk.
> 
> In OMAP code we handle IP resets through the hwmod code and I prefer
> that IP-centric approach to associating IP resets with a clock node.
> Perhaps the hwmod approach could serve as inspiration for a new generic
> way to reset modules.

OK, I'm not even slightly familiar with the hwmod code, but I keep
hearing about it, so I'll go take a quick look.
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