linux-kernel - Re: AXP803 I2C support / AXP devicetree-bindings

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Date:   Tue, 07 Nov 2017 16:20:43 +0800
From:   Icenowy Zheng <icenowy@...c.io>
To:     Chen-Yu Tsai <wens@...e.org>,
        Martin Blumenstingl <martin.blumenstingl@...glemail.com>
Cc:     devicetree <devicetree@...r.kernel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        Maxime Ripard <maxime.ripard@...e-electrons.com>,
        Quentin Schulz <quentin.schulz@...e-electrons.com>
Subject: Re: AXP803 I2C support / AXP devicetree-bindings


于 2017年11月7日 GMT+08:00 上午11:13:23, Chen-Yu Tsai <wens@...e.org> 写到:
> On Tue, Nov 7, 2017 at 6:39 AM, Martin Blumenstingl
> <martin.blumenstingl@...glemail.com> wrote:
>> Hello,
>> 
>> recently I discovered that there are some X-Powers AXP chips that
>> support both, Allwinner's own "RSB" as well as the I2C ("TWSI" in the
>> datasheet) busses.
>> 
>> one chip that supports both interfaces is the AXP803
>> the datasheet is linked in the public PINE64 wiki: [1] (direct link:
> [0])
> 
> All the RSB based PMICs support both modes. They start in I2C mode
> when cold booted.

I think it starts at a vendor-customized mode. In all PMICs sold
with Allwinner SoCs the mode is predefined to RSB.

In fact many registers in AXPs are vendor-customizable, see
the datasheets.

> 
>> 
>> currently the "x-powers,axp803" binding is "RSB" bus specific as it's
>> currently only listed in drivers/mfd/axp20x-rsb.c
>> 
>> was there a discussion about supporting both, the "RSB" and I2C bus
>> for one chip (for example the AXP803) in the past (I couldn't find
>> anything online)?
> 
> No. None of the boards actually use I2C instead of RSB. RSB mode is
> initialized by the boot loader. There is no easy way for the kernel to
> switch it back.
> 
>> what about the device-tree bindings in this case?
> 
> We can deal with it if someone actually comes up with a practical
> case needing it. Otherwise things go untested, which is not what
> we want.
> 
> ChenYu
> 
>> 
>> 
>> Regards
>> Martin
>> 
>> 
>> [0]
> http://files.pine64.org/doc/datasheet/pine64/AXP803_Datasheet_V1.0.pdf
>> [1]
> http://wiki.pine64.org/index.php/PINE_A64_Main_Page#Datasheets_for_Components_and_Peripherals