Re: [RFC next v1 5/5] arm64: dts: meson: g12a: x96-max: fix the Ethernet PHY reset line
From: Linus Walleij
Date: Sun Jun 09 2019 - 18:11:25 EST
On Sun, Jun 9, 2019 at 11:36 PM Martin Blumenstingl
> > If "snps,reset-active-low" was set it results in the sequence 1, 0, 1
> > if it is not set it results in the sequence 0, 1, 0.
> I'm changing this logic with earlier patches of this series.
> can you please look at these as well because GPIO_OPEN_SOURCE doesn't
> work with the old version of stmmac_mdio_reset() that you are showing.
OK but the logic is the same, just that the polarity handling is moved
> > The high (reset) is asserted by switching the pin into high-z open drain
> > mode, which happens by switching the line into input mode in some
> > cases.
> > I think the real reason it works now is that reset is actually active high.
> let me write down what I definitely know so far
> the RTL8211F PHY wants the reset line to be LOW for a few milliseconds
> to put it into reset mode.
> driving the reset line HIGH again takes it out of reset.
> Odroid-N2's schematics  (page 30) shows that there's a pull-up for
> the PHYRSTB pin, which is also connected to the NRST signal which is
Looks correct, R143 is indeed a pull up indicating that the line is
open drain, active low.
> > It makes a lot of sense, since if it resets the device when set as input
> > (open drain) it holds all devices on that line in reset, which is likely
> > what you want as most GPIOs come up as inputs (open drain).
> > A pull-up resistor will ascertain that the devices are in reset.
> my understanding is that the pull-up resistor holds it out of reset
> driving GPIOZ_15's (open drain) output LOW pulls the signal to ground
> and asserts the reset
Yep that seems correct.
Oh I guess it is this:
amlogic,tx-delay-ns = <2>;
- snps,reset-gpio = <&gpio GPIOZ_14 0>;
+ snps,reset-gpio = <&gpio GPIOZ_15 GPIO_OPEN_SOURCE>;
snps,reset-delays-us = <0 10000 1000000>;
Can you try:
snps,reset-gpio = <&gpio GPIOZ_15 (GPIO_ACTIVE_LOW | GPIO_OPEN_DRAIN)>;
Open source is nominally (and rarely) used for lines that are active high.
For lines that are active low, we want to use open drain combined
with active low.