Re: [PATCH RESEND 3/4] ARM: dts: imx6ul: phycore: Change USB LDO voltage for usb compliance

[Andrej Picej <andrej.picej@norik.com>]

On 12. 02. 22 06:46, Shawn Guo wrote:
> On Mon, Jan 31, 2022 at 09:05:25AM +0100, Andrej Picej wrote:
>> From: Yunus Bas <y.bas@phytec.de>
>>
>> According to the NXP usb compliance reference, the USB data lines for
>> Full/Low speed are connected to the ARM USB LDO, which is set to
>> minimum-voltage = 2.6V and maximum-voltage = 3.4 V. When the regulator
>> is deactivated, the data lines are defaulty driven with 2.6V, which is
>> not USB Full-Speed compliant. To be compliant, we need to activate the
>> USB LDO regulator and set it to the value of 3V, which is the specified
>> value in the USB specification.
>>
>> Signed-off-by: Yunus Bas <y.bas@phytec.de>
>> Signed-off-by: Andrej Picej <andrej.picej@norik.com>
>> ---
>>   arch/arm/boot/dts/imx6ul-phytec-phycore-som.dtsi | 5 +++++
>>   1 file changed, 5 insertions(+)
>>
>> diff --git a/arch/arm/boot/dts/imx6ul-phytec-phycore-som.dtsi b/arch/arm/boot/dts/imx6ul-phytec-phycore-som.dtsi
>> index 3cddc68917a0..2e03be3d43ec 100644
>> --- a/arch/arm/boot/dts/imx6ul-phytec-phycore-som.dtsi
>> +++ b/arch/arm/boot/dts/imx6ul-phytec-phycore-som.dtsi
>> @@ -83,6 +83,11 @@ eeprom@52 {
>>   	};
>>   };
>>   
>> +&reg_3p0 {
>> +	regulator-min-microvolt = <3000000>;
>> +	regulator-always-on;
> 
> Rather than setting it always-on, shouldn't the consumer of the
> regulator turn it on/off as needed?

Sorry for late response, but I had to look into this a bit to see the 
reason for using always-on.

The consumer should turn the regulator on/off, but the consumer doesn't 
do that. If regulator is not specified as always-on the regulator stays 
in disabled state, even when usb device is used. That's why this was 
added here.

This should probably be fixed on consumer side. If you want I can drop 
the patch from this series and submit the fixed version when the stuff 
gets resolved.

BR,
Andrej