linux-kernel - Re: [PATCH v2 4/4] clk: dt: Introduce always-on clock domain documentation

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Date:	Thu, 19 Feb 2015 10:55:16 +0100
From:	Geert Uytterhoeven <geert@...ux-m68k.org>
To:	Lee Jones <lee.jones@...aro.org>
Cc:	Rob Herring <robherring2@...il.com>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Mike Turquette <mturquette@...aro.org>,
	Stephen Boyd <sboyd@...eaurora.org>, kernel@...inux.com,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>
Subject: Re: [PATCH v2 4/4] clk: dt: Introduce always-on clock domain documentation

Hi Lee,

On Thu, Feb 19, 2015 at 10:42 AM, Lee Jones <lee.jones@...aro.org> wrote:
>> What kind of clocks are these? What do they control?
>> Memory controllers? Bus controllers?
>>
>> They must control some device(s), so there should be one or more device
>> nodes in DT that reference these clocks.
>> As soon as that information is in DT, support can be added to Linux to
>> make sure the "critical" clocks stay enabled, either through a real driver,
>> or through platform code.
>
> Some do, some don't.  For instance, we have one clock which controls
> SPI and I2C that must not be turned off.  We discovered this then when
> a suspend was attempted and the board refused to resume.  This clock
> also runs one of the critical interconnects that runs from the a9.  It
> would be wrong to remove the clk_disable() attempt from the SPI/I2C
> drivers because the same IP on another board might be controlled by a
> different clock which is able to be gated.
>
> There are also clocks which control other interconnects that are not
> connected to any device drivers.  If we fail to take references for
> them before clk_disable_unused() is called, again the board hangs.  We
> even lose JTAG support.

Interconnects are buses. Can't you represent those buses in the DT
hierarchy, and give them clocks properties?

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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