Messages in this thread | | | Date | Mon, 13 Jul 2015 13:08:14 +0530 | From | Vaibhav Hiremath <> | Subject | Re: [PATCH 3/6] mfd: devicetree: bindings: 88pm800: Add DT property for 32KHz output enable |
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On Monday 13 July 2015 01:01 PM, Krzysztof Kozlowski wrote: > On 13.07.2015 16:24, Vaibhav Hiremath wrote: >> >> >> On Saturday 11 July 2015 12:41 PM, Krzysztof Kozlowski wrote: >>> W dniu 09.07.2015 o 20:47, Vaibhav Hiremath pisze: >>>> 88PM800 family of device supports output of 32KHz clock (low jitter) >>>> on CLK32K2/3 pin which can be supplied to other peripherals on the >>>> board. >>>> >>>> This patch adds the devicetree binding to enable this feature. >>>> >>>> Signed-off-by: Vaibhav Hiremath <vaibhav.hiremath@linaro.org> >>>> --- >>>> Documentation/devicetree/bindings/mfd/88pm800.txt | 6 ++++++ >>>> 1 file changed, 6 insertions(+) >>>> >>>> diff --git a/Documentation/devicetree/bindings/mfd/88pm800.txt >>>> b/Documentation/devicetree/bindings/mfd/88pm800.txt >>>> index dec842f..ae1311c 100644 >>>> --- a/Documentation/devicetree/bindings/mfd/88pm800.txt >>>> +++ b/Documentation/devicetree/bindings/mfd/88pm800.txt >>>> @@ -9,6 +9,12 @@ Required parent device properties: >>>> - #interrupt-cells : should be 1. >>>> The cell is the 88pm80x local IRQ number >>>> >>>> +Optional properties : >>>> + - marvell,88pm800-32khz-xolj-out-en : If set, driver will enable >>>> low jitter >>>> + version of 32Khz clock output on >>> >>> I am not sure if I understand it correctly. The hardware always has such >>> clocks and you only want to enable/disable it in DT? Any reasons why >>> these should not be enabled always? >>> >> >> Small amount of Power savings... >> Although currently I do not have power numbers to justify this. >> >> As per spec, (it only talks about power consumption in power down state) >> >> Power-down State => VSYS > 2.8 => 4.5 μA >> CLK32K2 = 0 => 18 μW > > This would be a power saving if it could be enabled/disabled runtime. > But with DT you will either: > 1. enable it always so there won't be any power saving, > 2. disable it always so there won't be such clock. > > I can find a use case - when on some boards the clock output is not > wired to anything so it cannot be used. In other cases (there is some > potential user) this should be triggered per-use (runtime enabled/disabled). >
Exactly,
> Do you have such case? I mean boards where this is not connected at all > and boards where this is used? >
The PXA1928 based board which I have,
CLK32K1 (G3 pad) = Used by Wireless chip CLK32K2 (G11 pad) = Not connected to anything, so we need to disable this output
>>> Enabling it in DT does not look like a job for DT. Maybe you there >>> should be just a clock driver (clock provider)? >>> >> >> It's init time (and one time) settings, wouldn't clock-provider >> be overkill for this? > > The clock provider would be a proper way to do it and some PMICs I know > do this. Examples are max77686 and s5m8767/s2mps11. These are PMICs used > for Samsung SoCs. They have two or three 32kHz clocks. >
This is good to know. Let me take a look at these drivers.
Thanks, Vaibhav
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