Re: [linux-sunxi] [PATCH 2/5] arm: allwinner: a64: drop the dummy vcc3v3 regulator in Pine64 DT

[Andre Przywara <andre.przywara-5wv7dgnIgG8@public.gmane.org>]

Hi,

On 21/07/17 13:49, Icenowy Zheng wrote:
> 
> 
> 于 2017年7月21日 GMT+08:00 下午8:45:39, Andre Przywara <andre.przywara-5wv7dgnIgG8@public.gmane.org> 写到:
>> Hi,
>>
>> On 19/07/17 17:10, Icenowy Zheng wrote:
>>> The Pine64 DT used to contain a dummy vcc3v3 regulator, in order to
>>> satisfy some device nodes when proper AXP803 regulator support is
>>> available. It's in fact the DCDC1 regulator of AXP803.
>>>
>>> Drop the dummy regulator, and fix the reference of this regulator to
>>> DCDC1.
>>
>> Do we really need to have this?
>> While I see that this is technically correct, it breaks older kernels,
>> which miss the AXP driver. So we can't use this DT for syncing it into
>> U-Boot anymore, while still expecting various kernels (for instance
>> from
>> distribution installers) to work via UEFI (for which U-Boot provides
>> the
>> DT). That would be a shame, because we start to see generic arm64
>> distribution installers to work out of the box.
>>
>> I see these solutions:
>> 1) We drop this patch, instead add a comment that technically it's
>> DCDC1. I believe we can't really turn off DCDC1 anyway.
>> 2) We keep theses patches, but don't sync them to U-Boot to have a
>> universal DT in there which works with every kernel.
>> 3) We keep these patches *and* sync them to U-Boot, but add the fixed
>> regulator back in via a U-Boot specific .dtsi "overlay" snippet. This
>> would take care of the parts that break compatibility. The end result
>> would be similar to 2), then.
>>
>> The easiest and most maintainable would be 1), but I am OK with 3) as
>> well, though I am not sure this won't get messy in the future and will
>> work for every change that we make.
>>
>> What do you think?
> 
> 4) Do nothing.
> 
> We only promise old DTs will run with newer kernel, but
> we don't promise newer DTs to run with old kernel.And
> U-Boot is intended to update less frequently than Linux.
> 
> When updateing U-Boot, please update kernel as well.

Which means you tie your firmware to a kernel. I know this is the old
embedded approach, but we should really get rid of this, as I don't see
how this will work nicely with the Pinebook, for instance (which is not
really "embedded" anymore).
U-Boot sits on the SPI flash there, and you are expected to just run any
(not only Linux) distribution from a USB pen drive, for instance, with
that one firmware version, using UEFI. This already works today, but is
only sustainable if we have forward DT compatibility as well.


Cheers,
Andre.

>>
>>> Signed-off-by: Icenowy Zheng <icenowy-h8G6r0blFSE@public.gmane.org>
>>> ---
>>>  arch/arm64/boot/dts/allwinner/sun50i-a64-pine64.dts | 9 +--------
>>>  1 file changed, 1 insertion(+), 8 deletions(-)
>>>
>>> diff --git a/arch/arm64/boot/dts/allwinner/sun50i-a64-pine64.dts
>> b/arch/arm64/boot/dts/allwinner/sun50i-a64-pine64.dts
>>> index ac31c9477b25..68a47d9b07d9 100644
>>> --- a/arch/arm64/boot/dts/allwinner/sun50i-a64-pine64.dts
>>> +++ b/arch/arm64/boot/dts/allwinner/sun50i-a64-pine64.dts
>>> @@ -61,13 +61,6 @@
>>>  	chosen {
>>>  		stdout-path = "serial0:115200n8";
>>>  	};
>>> -
>>> -	reg_vcc3v3: vcc3v3 {
>>> -		compatible = "regulator-fixed";
>>> -		regulator-name = "vcc3v3";
>>> -		regulator-min-microvolt = <3300000>;
>>> -		regulator-max-microvolt = <3300000>;
>>> -	};
>>>  };
>>>  
>>>  &ehci0 {
>>> @@ -108,7 +101,7 @@
>>>  &mmc0 {
>>>  	pinctrl-names = "default";
>>>  	pinctrl-0 = <&mmc0_pins>;
>>> -	vmmc-supply = <&reg_vcc3v3>;
>>> +	vmmc-supply = <&reg_dcdc1>;
>>>  	cd-gpios = <&pio 5 6 GPIO_ACTIVE_HIGH>;
>>>  	cd-inverted;
>>>  	disable-wp;
>>>
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