linux-kernel - Re: [RFC PATCH] clk: add extension API

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Message-ID: <20120531085432.GK5377@arwen.pp.htv.fi>
Date:	Thu, 31 May 2012 11:54:33 +0300
From:	Felipe Balbi <balbi@...com>
To:	Peter De Schrijver <pdeschrijver@...dia.com>
Cc:	Felipe Balbi <balbi@...com>, Stephen Boyd <sboyd@...eaurora.org>,
	Russell King <linux@....linux.org.uk>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	Mike Turquette <mturquette@...com>
Subject: Re: [RFC PATCH] clk: add extension API

Hi,

On Thu, May 31, 2012 at 11:31:31AM +0300, Peter De Schrijver wrote:
> On Thu, May 31, 2012 at 10:18:42AM +0200, Felipe Balbi wrote:
> > * PGP Signed by an unknown key
> > 
> > On Thu, May 31, 2012 at 10:51:25AM +0300, Peter De Schrijver wrote:
> > > On Wed, May 30, 2012 at 10:52:31AM +0200, Stephen Boyd wrote:
> > > > On 5/29/2012 2:58 AM, Peter De Schrijver wrote:
> > > > > Add an extension API for clocks. This allows clocktypes to provide extensions
> > > > > for features which are uncommon and cannot be easily mapped onto normal clock
> > > > > framework concecpts. eg: resetting blocks, configuring clock phase etc.
> > > > 
> > > > This seems rather generic. Why not add more specific APIs/concepts like
> > > > clk_reset(), clk_set_phase(), etc.? If they don't map, maybe we should
> > > > make them map.
> > > > 
> > > 
> > > Some of those might be very SoC specific. Eg OMAP doesn't need software
> > > controlled modulereset. I don't think we should add a new function to the
> > 
> > it depends on what you call modulereset. We have soft-reset logic hidden
> > under the hood, it's done before device creation, so drivers (most of
> > them) assume we're probe with the IP in reset state.
> > 
> > What I wonder most is if this should be done at the clock level or at
> > the device level. In the end you reset the IP block, not the clock,
> > right ?
> 
> Yes. but, every block has at least 1 clock and thus the mapping is identical
> down to the register level. Ie. we could do this outside the clockframework,

What if a module needs two clocks and you drive the reset on both of the
clocks ? What would happen ?

> but then we would have the keep a list of IDs (1 per module) which the drivers
> can use to call some tegra reset function which would in the end use registers
> in the same memory area to cause a reset. (the registers controlling
> modulereset are interleaved with those controlling the enable/disable of the
> main moduleclock and bitpositions are identical)

Well, under a generic device-level API, you could just call an internal
clk_reset() function because you know which clocks feed into which
devices anyway. It could look something like:

on Tegra:

device_reset(dev)
	-> dev_pm_domain->reset()
		-> tegra_periph_reset()

on OMAP:

device_reset(dev)
	-> dev_pm_domain->reset()
		-> omap_hwmod_reset()


btw:

tegra_periph_reset(....)
{
	tegra_periph_reset_assert(...);
	udelay(2);
	tegra_periph_reset_deassert(...);
}

-- 
balbi

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