linux-kernel - Re: [PATCH v2 2/3] ARM: dts: sunxi: add support for Orange Pi Zero board

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Date:   Sat, 3 Dec 2016 00:37:34 +0800
From:   Chen-Yu Tsai <wens@...e.org>
To:     Andre Przywara <andre.przywara@....com>
Cc:     Icenowy Zheng <icenowy@...c.xyz>,
        Hans de Goede <hdegoede@...hat.com>,
        Maxime Ripard <maxime.ripard@...e-electrons.com>,
        Jonathan Corbet <corbet@....net>, Chen-Yu Tsai <wens@...e.org>,
        Mark Rutland <mark.rutland@....com>,
        Russell King <linux@...linux.org.uk>,
        Vishnu Patekar <vishnupatekar0510@...il.com>,
        Arnd Bergmann <arnd@...db.de>,
        "linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>
Subject: Re: [PATCH v2 2/3] ARM: dts: sunxi: add support for Orange Pi Zero board

On Sat, Dec 3, 2016 at 12:10 AM, Andre Przywara <andre.przywara@....com> wrote:
> Hi,
>
> On 02/12/16 14:32, Icenowy Zheng wrote:
>>
>>
>> 02.12.2016, 22:30, "Hans de Goede" <hdegoede@...hat.com>:
>>> Hi,
>>>
>>> On 02-12-16 15:22, Icenowy Zheng wrote:
>>>>  01.12.2016, 17:36, "Maxime Ripard" <maxime.ripard@...e-electrons.com>:
>>>>>  On Mon, Nov 28, 2016 at 12:29:07AM +0000, André Przywara wrote:
>>>>>>   > Something more interesting happened.
>>>>>>   >
>>>>>>   > Xunlong made a add-on board for Orange Pi Zero, which exposes the
>>>>>>   > two USB Controllers exported at expansion bus as USB Type-A
>>>>>>   > connectors.
>>>>>>   >
>>>>>>   > Also it exposes a analog A/V jack and a microphone.
>>>>>>   >
>>>>>>   > Should I enable {e,o}hci{2.3} in the device tree?
>>>>>>
>>>>>>   Actually we should do this regardless of this extension board. The USB
>>>>>>   pins are not multiplexed and are exposed on user accessible pins (just
>>>>>>   not soldered, but that's a detail), so I think they qualify for DT
>>>>>>   enablement. And even if a user can't use them, it doesn't hurt to have
>>>>>>   them (since they are not multiplexed).
>>>>>
>>>>>  My main concern about this is that we'll leave regulators enabled by
>>>>>  default, for a minority of users. And that minority will prevent to do
>>>>>  a proper power management when the times come since we'll have to keep
>>>>>  that behaviour forever.
>>>>
>>>>  I think these users can add a 'fdt set /xxx/xxx status "disabled" ' .
>>>
>>> I don't think that will be necessary I'm pretty sure these extra usb
>>> ports do not have a regulator for the Vbus, they just hook directly
>>> to the 5V rail, can someone with a schematic check ?
>>
>> We seems to have still no schematics for the add-on board.
>
> From looking at the picture of that expansion board on the Aliexpress
> page and chasing the tracks, there is clearly no voltage regulator on
> there, it's just passive components. The 5V pin from the headers is
> routed forth and back between the two layers via some vias directly to
> the 5V pins of the USB sockets.
>
>> But something is sure is that there's no any regulator-related pins
>> on the add-on pinout. There's only USB DM and DP pins.
>>
>> So the Vbus must be directly connected to +5V.
>
> So yes, it is.
>
> But I think the question is moot anyways, since we don't provide DT
> support for that add-on board at that point anyways.
> One could imagine another board, though, which has regulators switched
> by GPIOs, but that would be their problem and they would have regulators
> specified in their specific DT snippet, then.
>
> So to summarize:
> - For that specific Orange Pi Zero board which we discuss the DT for
> there is no regulator support for the additional USB ports. Thus nothing
> we could turn off to save power.
> - A user could just take these USB brackets with pin headers that are so
> common in PCs to connect additional USB ports to the back of the box.
> One just needs to re-sort the pins, which is a matter of a minute.
> - As long as we don't provide any easy way of handling DT changes, we
> should enable the USB ports for the sake of the users of either those
> brackets or the expansion board. Any more sophisticated USB expansion
> board with regulators would need to amend the DT anyway.
>
> Does that make sense?

Sounds good to me.

ChenYu