Hi,
my point is not that your patch is good enough.
My point is that it would be very difficult to maintain backward
compatibility with this device tree once proper driver support is
implemented.
On 5/21/22 07:26, qianfan wrote:
在 2022/5/20 4:54, Evgeny Boger 写道:
Hi qianfan,
As Allwinner A40i user, let me first thank you for your effort for
making better upstream support for R40!
However, I would strongly suggest *not* to add USB support to one
more Allwinner SoC in this particular way.
The problem is, this approach consists of a number of carefully
crafted hacks in device tree to make current drivers work on
Allwinner hardware without modification to the drivers.
a few examples:
1) please notice how ohci0 and ehci0 nodes do not contain reference
to usb phy. It is done intentionally, otherwise EHCI will reset musb
mode.
Of course omitting phy reference here is also completely breaking
power cycling in case of usb error and otherwise messes with a power
management.
2) one must always enable ohci, ehci and usb_otg nodes at the same
time. If one forgets to enable ohci/ehci nodes while enabling usb_otg
node, the system will silently fail to work as USB host.
3) For host-only mode we still have to enable usb_otg node despite no
role switching is needed. That's because phy reference is missing in
ehci/ohci, so the ehci/ohci driver won't enable the PHY.
Also I might be wrong, but I think phy won't be routed to ehci/ohci
controllers is this case.
4) musb host controller is initialized and present to hardware though
never actually used
To summarize, not only the resulting device tree is not describing
the hardware properly, it is creating device tree configuration which
will be very hard to support in future, once proper driver support is
in place.
PHY setting is did in MUSB driver, so we need enable MUSB regardless
of host mode.
I know your's point, OHCI/EHCI need do more works to init USBPHY, it
shoule be able to work
in dependently, but I don't have the ability to deal with these things
right now, I need
learn more things about OHCI/EHCI, that's a long-term goal.
So now I need to make the whole usb work and do some tests as much as
possible,
hoping to merge this patch into master. Some other optimizations can
be made later.
Thanks for yours guide.
At Wiren Board kernel tree we tried to untangle this issue [1-6].
Unfortunately I didn't have time to prepare it for kernel submission
yet, but I think I better submit it as RFC to get a feedback from you
and others.
[1]
https://github.com/wirenboard/linux/commit/359abbbd86ddff4d3c61179c882c286de32bb089
[2]
https://github.com/wirenboard/linux/commit/6327f9d7972c21b229fb83457fdde643b31553f9
[3]
https://github.com/wirenboard/linux/commit/f01f4c66758bde460a4d8c5b54ecee3b585c0232
[4]
https://github.com/wirenboard/linux/commit/c27598ad601e5a46f624b73412a531d6f1f63d37
[5]
https://github.com/wirenboard/linux/commit/5796d6eebb86b32a3751b2038b63af46f94954b3
[6]
https://github.com/wirenboard/linux/commit/0928a675d875f9c2849fd3a9888f718bbb673bda
--
Kind regards,
Evgeny Boger
CTO @ Wiren Board
+49 3046690053
https://wirenboard.com/
