Hi Lee,
On Thu, Feb 19, 2015 at 11:28 AM, Lee Jones <lee.jones@xxxxxxxxxx> wrote:
> On Thu, 19 Feb 2015, Geert Uytterhoeven wrote:
>> 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.
>
> Okay so ...
>
> /*
> * ICNs are not visible/controllable in Linux, but references to their
> * clocks must be obtained and retained or the platform will become
> * irrecoverably unresponsive.
> */
> interconnects@0 {
> compatible = "always-on-clk-domain";
st,...flexgen...
> clocks = <&clk_s_c0_flexgen CLK_ICN_SBC>,
> <&clk_s_c0_flexgen CLK_ICN_LMI>,
> <&clk_s_c0_flexgen CLK_ICN_CPU>,
> <&clk_s_c0_flexgen CLK_TX_ICN_DMU>;
> };
And then you can have platform code that binds against st,...flexgen...,
and enables all referenced clocks.
Alternatively, if you have power domains, you can add a reference to
the power domain, and let the power domain driver handle it.
Gr{oetje,eeting}s,
Geert
--
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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