Re: [linux-sunxi] [PATCH 6/8] ARM: dts: axp209: Add usb_power_supply child node to the ax209 node

[Hans de Goede <hdegoede-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>]

Hi,

On 31-07-15 08:35, Bruno Prémont wrote:
> On Fri, 31 Jul 2015 14:14:28 +0800 Chen-Yu Tsai wrote:
>> On Fri, Jul 31, 2015 at 1:51 PM, Bruno Prémont wrote:
>>> Hi ChenYu,
>>>
>>> On Fri, 31 Jul 2015 13:31:53 +0800 Chen-Yu Tsai wrote:
>>>> Hi Hans,
>>>>
>>>> On Wed, Jun 10, 2015 at 5:37 AM, Hans de Goede wrote:
>>>>> Add a node representing the usb power supply part of the axp209 pmic, note
>>>>> that the usb power supply and the (to be added later) ac power supply will
>>>>> each have their own child-node, so that they can be separately specified
>>>>> as power-supply for other nodes using a power-supply property with a
>>>>> phandle pointing to the right axp209 child-node.
>>>>>
>>>>> Signed-off-by: Hans de Goede <hdegoede-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
>>>>> ---
>>>>>   arch/arm/boot/dts/axp209.dtsi | 5 +++++
>>>>>   1 file changed, 5 insertions(+)
>>>>>
>>>>> diff --git a/arch/arm/boot/dts/axp209.dtsi b/arch/arm/boot/dts/axp209.dtsi
>>>>> index 24c935c..051ab3b 100644
>>>>> --- a/arch/arm/boot/dts/axp209.dtsi
>>>>> +++ b/arch/arm/boot/dts/axp209.dtsi
>>>>> @@ -89,4 +89,9 @@
>>>>>                          regulator-name = "ldo5";
>>>>>                  };
>>>>>          };
>>>>> +
>>>>> +       usb_power_supply: usb_power_supply {
>>>>> +               compatible = "x-powers,axp202-usb-power-supply";
>>>>> +               status = "disabled";
>>>>
>>>> Is there any reason to have this disabled by default?
>>>> AFAIK this is not something configurable in hardware,
>>>> and the driver just gives readouts and status updates.
>>>
>>> There are some devices that only have 'AC-IN' instead of usb/otg power
>>> (set-top boxes) so having the devices tell what power sources they
>>> have makes sense (otherwise those that have ac-in instead of otg would
>>> have to disable usb_power_supply) and avoids confusion by explicitly
>>> stating presence in device dts.
>>
>> That's true. But this is a bit of hardware inside the AXP.
>> If it's power isn't routed, it should report it, shouldn't it?
>
> If the device does not use the input there are two cases:
> - ac-in and usb/otg in short-circuited (there is a bit in AXP registers
>    to provide this indication)
> - the unused one is just not connected/connectable
>
> In either case the voltage of the unused/unusable branch is not really
> useful, nor is it useful to have it show up in sysfs.

Exactly my thinking on this, +1 .

>> And normal users would probably expect to read the input
>> voltage/current/status through sysfs (or maybe hwmon?),
>> instead of not finding the device and having to look through
>> the DTS.
>
> Only those supplies effectively present (in-use or with connectors
> to eventually use them) should be visible in sysfs.
> Having more of them will just confuse the users, they would be searching
> how they can connect the supply while there is no means to do so
> except soldering to the tiny AXP pins.

+1

Regards,

Hans
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