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

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Message-ID: <CAMuHMdW=kV+zx=Uq7y7SyrH3eQyWsdfWjuLFMAKQjPhX-QaPPA@mail.gmail.com>
Date:	Thu, 19 Feb 2015 11:18:30 +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 11:11 AM, Lee Jones <lee.jones@...aro.org> wrote:
> On Thu, 19 Feb 2015, Geert Uytterhoeven wrote:
>> 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?
>
> So instead of this nice succinct, simple, cover all bases
> (interconnects was just an example, there are bound to be others),
> generic framework, you are suggesting to write drivers for devices
> which other than "don't turn my clocks off", Linux can't actually see
> or control?

DT describes the hardware, not behavior.

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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