linux-kernel - Re: [RFC PATCH 2/2] of/clk: use "clkops-clocks" to specify clocks handled by clock

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Date:	Mon, 04 Aug 2014 17:21:49 +0200
From:	Laurent Pinchart <laurent.pinchart@...asonboard.com>
To:	Geert Uytterhoeven <geert@...ux-m68k.org>
Cc:	Grant Likely <grant.likely@...retlab.ca>,
	Grygorii Strashko <grygorii.strashko@...com>,
	Geert Uytterhoeven <geert+renesas@...der.be>,
	Ulf Hansson <ulf.hansson@...aro.org>,
	Kevin Hilman <khilman@...aro.org>,
	Mike Turquette <mturquette@...aro.org>,
	Tomasz Figa <tomasz.figa@...il.com>,
	Ben Dooks <ben.dooks@...ethink.co.uk>,
	Simon Horman <horms@...ge.net.au>,
	Magnus Damm <magnus.damm@...il.com>,
	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	"linux-sh@...r.kernel.org" <linux-sh@...r.kernel.org>,
	Linux PM list <linux-pm@...r.kernel.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	"linux-omap@...r.kernel.org" <linux-omap@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH 2/2] of/clk: use "clkops-clocks" to specify clocks handled by clock_ops domain

Hi Geert,

On Monday 04 August 2014 13:28:32 Geert Uytterhoeven wrote:
> On Wed, Jul 30, 2014 at 2:06 AM, Laurent Pinchart wrote:
> > The third option would require storing the clocks lists in device drivers.
> > I believe this is our best option, as a trade-off between simplicity and
> > versatility. Drivers that use runtime PM already need to enable it
> > explicitly when probing devices. Passing a list of clock names to runtime
> > PM at that point wouldn't complicate drivers much. When the clocks list
> > isn't SoC- dependent it could be stored as static information. Otherwise
> > it could be derived from DT (or any other source of hardware description)
> > using C code, offering all the versatility we need.
> > 
> > The only drawback of this solution I can think of right now is that the
> > runtime PM core couldn't manage device clocks before probing the device.
> > Specifically device clocks couldn't be managed if no driver is loaded for
> > that device. I somehow recall that someone raised this as being a
> > problem, but I can't remember why.
> 
> Perhaps you're thinking of clocks that were enabled (by the boot loader or
> implicit reset state) before running Linux, and aren't disabled?

That wasn't the reason, I know that clk_disable_unused() takes care of that 
problem (provided the clock drivers behave correctly, the commit you mention 
below shows that's not always the case, but that's an unrelated issue).

> That was fixed by commit bb178da701382a230e26d90cf94e8a24b280e0d9
> ("clk: shmobile: mstp: Fix the is_enabled() operation").

-- 
Regards,

Laurent Pinchart

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