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

[Chen-Yu Tsai]

On Fri, Jul 31, 2015 at 5:11 PM, Hans de Goede <hdegoede at redhat.com> wrote:
> Hi,
>
>
> On 31-07-15 11:00, Chen-Yu Tsai wrote:
>>
>> On Fri, Jul 31, 2015 at 4:31 PM, Hans de Goede <hdegoede at redhat.com>
>> wrote:
>>>
>>> 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 at redhat.com>
>>>>>>>> ---
>>>>>>>>    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
>>
>>
>> OK. So mostly tablets and dev boards would benefit from having both
>> power supplies. Is there a preference for usb-power-supply over
>> vbus-det-gpio if both are available? Or just list them both and
>> let the driver sort it out?
>
>
> So far I've simply stuck with whatever the fex file uses, if both
> are specified the driver will prefer the gpio, but that is not
> documented behavior. IMHO it would be better to pick and specify
> only one.

>From a functional standpoint, if usb-power-supply is available,
using it would be better because:

a) VBUS detection should be much better (IIRC cutoff at 4.4V)
b) Controllable max current draw
c) Can see the current draw

Of course not all boards would work. I think I even have a board
that is only half powered on when only USB VBUS is used.

ChenYu