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

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Message-ID: <CAMuHMdV8_uKQQgYkRPFOBgrqgw_y9A7T84ukfgWZpJmTL0eFCQ@mail.gmail.com>
Date:	Wed, 25 Mar 2015 05:11:51 +0100
From:	Geert Uytterhoeven <geert@...ux-m68k.org>
To:	Lee Jones <lee.jones@...aro.org>
Cc:	Mike Turquette <mturquette@...aro.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	kernel@...inux.com, Stephen Boyd <sboyd@...eaurora.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>
Subject: Re: [PATCH v3 0/4] clk: st: New always-on clock domain

Hi Lee,

On Mon, Mar 9, 2015 at 10:28 AM, Lee Jones <lee.jones@...aro.org> wrote:
> On Fri, 06 Mar 2015, Mike Turquette wrote:
>> Quoting Lee Jones (2015-03-04 04:00:03)
>> > Mike,
>> >
>> > Do you want me to resend this set with Robert's Reviewed-by applied,
>> > or are you happy to apply it yourself?
>>
>> No need for the resend. I am hoping for a final review from a DT human.
>>
>> This approach looks fine to me. In practice I think it is restricted to
>> hardware blocks that don't exist in DT yet (e.g. no driver, in the case
>> of your interconnect) and that restriction is probably for the best.
>
> Agreed.

I think this restriction should be documented in the DT binding more clearly,
as adding a "clk-always-on" node prohibits you from handling the clock
correctly in
the future.

Still, for simple devices where you don't have a driver, but have "predictable"
bindings (e.g. a bus like "simple-pm-bus"), I think it's better to add
a device node
for that simple device now, incl. a reference to the clock, and have a simple
driver that binds to the device, or platform code that looks for a
compatible node,
and enables the clock. That way you don't have to make any chances to the DTS
later, when you'll have a real driver.

>> > > 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.

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds
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