Re: [PATCH v2 4/4] clk: dt: Introduce always-on clock domain documentation
From: Lee Jones
Date: Thu Feb 19 2015 - 05:28:19 EST
On Thu, 19 Feb 2015, Geert Uytterhoeven wrote:
> 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.
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.
compatible = "always-on-clk-domain";
clocks = <&clk_s_c0_flexgen CLK_ICN_SBC>,
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