AXP803 I2C support / AXP devicetree-bindings

AXP803 I2C support / AXP devicetree-bindings

[Martin Blumenstingl]

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])

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)?
what about the device-tree bindings in this case?


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

AXP803 I2C support / AXP devicetree-bindings

[Chen-Yu Tsai]

On Tue, Nov 7, 2017 at 6:39 AM, Martin Blumenstingl
<martin.blumenstingl@googlemail.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.

>
> 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

AXP803 I2C support / AXP devicetree-bindings

[Icenowy Zheng]

? 2017?11?7? GMT+08:00 ??11:13:23, Chen-Yu Tsai <wens@csie.org> ??:
> On Tue, Nov 7, 2017 at 6:39 AM, Martin Blumenstingl
> <martin.blumenstingl@googlemail.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

AXP803 I2C support / AXP devicetree-bindings

[Martin Blumenstingl]

Hi ChenYu,

On Tue, Nov 7, 2017 at 4:13 AM, Chen-Yu Tsai <wens@csie.org> wrote:
> On Tue, Nov 7, 2017 at 6:39 AM, Martin Blumenstingl
> <martin.blumenstingl@googlemail.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 did not know that - thank you for that info!

>>
>> 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.
I'm not trying to change this on an existing board

>> 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.
OK, thank you for this information

if there is a valid use-case for this: would you like to see a RfC
patch-series (along with a description why it's needed) or discuss
this further before sending any patches?


Regards
Martin