linux-kernel - Re: [PATCH v3 0/4] clk: st: New always-on clock domain

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Date:	Fri, 27 Feb 2015 21:49:41 +0000
From:	Lee Jones <lee.jones@...aro.org>
To:	Robert Jarzmik <robert.jarzmik@...e.fr>
Cc:	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	mturquette@...aro.org, sboyd@...eaurora.org, kernel@...inux.com,
	devicetree@...r.kernel.org
Subject: Re: [PATCH v3 0/4] clk: st: New always-on clock domain

On Fri, 27 Feb 2015, Robert Jarzmik wrote:

> Lee Jones <lee.jones@...aro.org> writes:
> 
> > v2 => v3:
> >   - Ensure DT actually reflects h/w
> >     - i.e. Nodes should not contain a mishmash of different IP
> >       blocks, but should identify related h/w.  In the current
> >       example we use interconnects
> >   - Change naming from clkdomain to clk-always-on
> >   - Place "do not abuse" warning in documentation
> >
> > v1 => v2:
> >   - Turned the ST specific driver into a generic one
> >   
> > Hardware can have a bunch of clocks which must not be turned off.
> > If drivers a) fail to obtain a reference to any of these or b) give
> > up a previously obtained reference during suspend, the common clk
> > framework will attempt to turn them off and the hardware will
> > subsequently die.  The only way to recover from this failure is to
> > restart.
> >   
> > To avoid either of these two scenarios from catastrophically
> > disabling the running system we have implemented a clock domain
> > where clocks are consumed and references are taken, thus preventing
> > them from being shut down by the framework.
> 
> Hi Lee,
> 
> I wonder why there is a need for a new clock when CLK_IGNORE_UNUSED does
> exist. What is the usecase that is covered by this patchset which is not used by
> CLK_IGNORE_UNUSED clock flag ?
> 
> And if that reason exists, I'd like to find it in the commit message.

The problem is applying that flag in a generic way.

However, I guess you haven't seen this [1] yet?

[1] https://lkml.org/lkml/2015/2/27/548

-- 
Lee Jones
Linaro STMicroelectronics Landing Team Lead
Linaro.org │ Open source software for ARM SoCs
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