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

From: Geert Uytterhoeven
Date: Thu Feb 19 2015 - 05:18:36 EST

Hi Lee,

On Thu, Feb 19, 2015 at 11:11 AM, Lee Jones <lee.jones@xxxxxxxxxx> wrote:
> On Thu, 19 Feb 2015, Geert Uytterhoeven wrote:
>> On Thu, Feb 19, 2015 at 10:42 AM, Lee Jones <lee.jones@xxxxxxxxxx> 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.



Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@xxxxxxxxxxxxxx

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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