[linux-sunxi] [PATCH 10/10] ARM: dts: sun8i: Add SY8106A regulator to Orange Pi PC

Maxime Ripard p??e v St 26. 07. 2017 v 13:44 +0200:

Hi,

On Wed, Jul 26, 2017 at 12:23:48PM +0200, Ond?ej Jirman wrote:

quoted

Hi,

icenowy at aosc.io p??e v St 26. 07. 2017 v 15:36 +0800:

quoted

quoted

quoted

quoted

Otherwse

quoted

+               regulator-max-microvolt = <1400000>;
+               regulator-ramp-delay = <200>;

Is this an actual constraint of the SoC? Or is it a characteristic
of the regulator? If it is the latter, it belongs in the driver.
AFAIK the regulator supports varying the ramp delay (slew rate).

I don't know...

Maybe I should ask Ondrej?

It is probably neither.

It is used to calculate a delay inserted by the kernel between setting
a new target voltage over I2C and changing the frequency of the CPU.
The actual delay is calculated by the difference between previous and
the new voltage.

I don't remember seeing anything in the datasheet of the regulator.
This is just some low value that works.

It would probably be dependent on the capacitance on the output of the
regulator, actual load (which varies), etc. So it is a board specific
value. One could measure it with an oscilloscope if there's a need to
optimize this.

If this is a reasonable default, then this should be in the
driver. You can't expect anyone to properly calculate a ramp delay and
have access to both a scope and the CPU power lines.

It translates to 1ms per 0.2V which is highly conservative. The real
times will be in 1-10us range. So I guess this could be a default in
the driver.

regards,
  o.

Maxime

-- 
Maxime Ripard, Free Electrons
Embedded Linux and Kernel engineering
http://free-electrons.com

-------------- next part --------------
A non-text attachment was scrubbed...
Name: signature.asc
Type: application/pgp-signature
Size: 833 bytes
Desc: This is a digitally signed message part
URL: <http://lists.infradead.org/pipermail/linux-arm-kernel/attachments/20170726/f70a2b27/attachment.sig>