linux-kernel - Re: [PATCH v2 4/7] dts: sun8i-h3: add UART1-3 to Orange Pi Plus

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Date:   Tue, 6 Sep 2016 11:04:38 +0800
From:   Chen-Yu Tsai <wens@...e.org>
To:     Maxime Ripard <maxime.ripard@...e-electrons.com>
Cc:     Chen-Yu Tsai <wens@...e.org>, Jorik Jonker <jorik@...pendief.biz>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Russell King <linux@...linux.org.uk>,
        devicetree <devicetree@...r.kernel.org>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 4/7] dts: sun8i-h3: add UART1-3 to Orange Pi Plus

On Tue, Sep 6, 2016 at 3:31 AM, Maxime Ripard
<maxime.ripard@...e-electrons.com> wrote:
> Hi Jorik,
>
> On Sat, Sep 03, 2016 at 02:09:32PM +0200, Jorik Jonker wrote:
>> On Fri, Sep 02, 2016 at 09:04:25AM +0200, Maxime Ripard wrote:
>> >Unfortunately, these pins can be used for other purposes as well, so
>> >we cannot make force that decision down to our users.
>>
>> Yes, but since the associated peripheral is disabled, the users are free to
>> configure other functions/peripherals, right? I mean something like this in
>> pseudo-DT:
>>
>> /soc/pio: pinctrl@...20800/uart1_pins:
>>   allwinner,pins = "PG6, PG7";
>> /soc/pio: pinctrl@...20800/foo0_pins:
>>   allwinner,pins = "PG6, PG7";
>>   ..
>> /soc/uart1: serial@...ial@...28400:
>>   pinctrl-0 = <&uart1_pins>;
>>   status = "disabled";
>> /soc/bar:
>>   pinctrl-0 = <&uart1_pins>;
>>   status = "disabled";
>>
>> Assuming Linux/DT allows this, this would force nothing, only offer choice
>> and ease of use.
>
> Hmm, sorry, I went over your patches too quickly...
>
> That's a great compromise I think. Chen-Yu, any opinion on this?

In short, I'm ok with it. But please put an explicit

    status = "disabled";

and probably a comment about how/where the peripheral can be
used in the board dts.

I intended to do this for the Banana Pis. Though my original plan
was to enable Raspberry Pi compatible peripherals by default, and
list the other peripherals that are defined by the vendor as
"disabled".

"Defined by the vendor" means that the vendor has some sort of
document associating the gpio header pins with the peripherals,
as shown in:

    http://www.orangepi.org/Docs/Pindefinition.html#CON3_Definition

This should make it easier for the average user to enable the
peripherals. I'm not sure we should list _all_ possible ones
though. That would make the list very large, and some might
end up never being used.


Regards
ChenYu