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

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Date:	Tue, 30 Oct 2012 12:02:05 -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 10/29/2012 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!) :-)

> 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.

Even ignoring that, we'd still need to API say device_reset(struct
device *dev) or device_reset(struct device *dev, const char *conid)
wouldn't we? That's really all I meant by a reset subsystem.

An alternative here would be to simply move Tegra's
tegra_periph_reset_{de,}assert() function prototypes into a header in
include/linux rather than mach-tegra/include/mach. However, I imagine at
least some other SoC needs a similar API, so a common API might be useful?
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