On 6 May 2016 at 00:42, Rob Herring [off-list ref] wrote:

On Thu, May 05, 2016 at 02:34:13PM +0200, Krzysztof Kozlowski wrote:

quoted

Hi,

This is a different, second try to fix usb3503+lan on Odroid U3 board
if it was initialized by bootloader (e.g. for TFTP boot).

First version:
http://www.spinics.net/lists/linux-usb/msg140042.html


Problem
=======
When Odroid U3 (usb3503 + smsc95xx + max77686) boots from network (TFTP),
the usb3503 and LAN smsc95xx do not show up in "lsusb". Hard-reset
is required, e.g. by suspend to RAM. The actual TFTP boot does
not have to happen. Just "usb start" from U-Boot is sufficient.

From the schematics, the regulator is a supply only to LAN, however
without toggling it off/on, the usb3503 hub won appear neither.


Solution
========
This is very similar to the MMC pwrseq behavior so the idea is to:
1. Move MMC pwrseq drivers to generic place,

You can do that, but I'm going to NAK any use of pwrseq bindings outside
of MMC. I think it is the wrong way to do things. The DT should describe

Huh, I didn't know that was your view of the mmc pwrseq bindings. Why
didn't you NAK them before?

the devices. If they happen to be "simple" then the core can walk the
tree and do any setup. For example, look for "reset-gpios" and toggle
that GPIO. There is no need for a special node.

quoted

2. Extend the pwrseq-simple with regulator toggling,
3. Add support to USB hub and port core for pwrseq,

We discussed this for USB already[1] and is why we defined how to add
USB child devices. The idea is not to add pwrseq to that.

I am not familiar with the USB discussion.

Still, let me give you some more background to the mmc pwrseq. The
idea from the mmc pwrseq bindings comes from the power-domain DT
bindings, as I thought these things were a bit related.
In both cases they are not directly a property of the device, but more
describing a HW dependency to allow the device to work.

One could probably use a child node instead of a phandle, but that
wasn't chosen back then. Of course you are the DT expert, but could
you perhaps tell me why a child node is better for cases like this?

Rob

[1] http://www.spinics.net/lists/linux-usb/msg134082.html

Kind regards
Uffe