Re: macb: probe of 10090000.ethernet failed with error -110

On Wed, 28 Nov 2018 18:28:58 PST (-0800), andrew@lunn.ch wrote:

quoted

This is all fine as long as Linux doesn't go and reset the phy again. Until
bafbdd527d56 ("phylib: Add device reset GPIO support") was the case.  After
that commit I believe phylib is resetting the phy while attempting to enter
unmanaged mode, which is now allowed in this particular chip.

Since it appears the phy is not usually described by the device tree but is
instead discovered by probing a MII-based ID register, it seems the best
place to put this is within the phy driver itself.  I find it's usually best
to describe things with code, so I hacked up something like

Talking to Florian, i was under the impression that you could not even
discover the device when its reset state what wrong. You could not
read the ID registers.

Your suggested change assumed you can discover the device. Is this
true?

Sorry, I can't tell that from reading the code.  Since our bootloader resets 
the phy into unmanaged mode I think that just deasserting reset should be OK, 
but I don't have much confidence in that -- once I run into one unexpected 
feature I start to expect more :)

It looks like there's already an expectation that at least the phy ID registers 
can be read between falling and rising edges of a reset, as that's how the 
fixups are handled.  Since the error message that shows up with a single 
(single as far as Linux is concerned, triple since a cold boot) reset rising 
edge still lists the phy by name I think that probing is working well enough, 
but I wouldn't be surprised if there's something in the middle that's gone 
wrong.  It's possible registering a fixup that does the double reset can get us 
through the probing sequence.

Maybe Atish or Paul can help out?  I'm a bit embarrassed to admit that I can't 
actually figure out how to boot the board any more, it's been a year since it's 
been my primary target and since I just to arch/riscv stuff now I rely them to 
test on the board...