Re: [PATCH 3/3] arm64: dts: rockchip: add clk-480m for ehci and ohci of rk3399

[Doug Anderson <dianders@google.com>]

Hi,

On Wed, Dec 14, 2016 at 2:11 AM, Xing Zheng <zhengxing@rock-chips.com> wrote:
> From: William wu <wulf@rock-chips.com>
>
> We found that the suspend process was blocked when it run into
> ehci/ohci module due to clk-480m of usb2-phy was disabled.
>
> The root cause is that usb2-phy suspended earlier than ehci/ohci
> (usb2-phy will be auto suspended if no devices plug-in).

This is really weird, but I can confirm it is true on my system too
(kernel-4.4 based).  At least I see:

[  208.012065] calling  usb1+ @ 4984, parent: fe380000.usb, cb: usb_dev_suspend
[  208.569112] calling  ff770000.syscon:usb2-phy@e450+ @ 4983, parent:
ff770000.syscon, cb: platform_pm_suspend
[  208.569113] call ff770000.syscon:usb2-phy@e450+ returned 0 after 0 usecs
[  208.569439] calling  fe380000.usb+ @ 4983, parent: platform, cb:
platform_pm_suspend
[  208.569444] call fe380000.usb+ returned 0 after 4 usecs


In general I thought that suspend order was supposed to be related to
probe order.  So if your probe order is A, B, C then your suspend
order would be C, B, A.  ...and we know for sure that the USB PHY
needs to probe _before_ the main USB controller.  If it didn't then
you'd get an EPROBE_DEFER in the USB controller, right?  So that means
that the USB controller should be suspending before its PHY.

Any chance this is somehow related to async probe?  I'm not a huge
expert on async probe but I guess I could imagine things getting
confused if you had a sequence like this:

1. Start USB probe (async)
2. Start PHY probe
3. Finish PHY probe
4. In USB probe, ask for PHY--no problems since PHY probe finished
5. Finish USB probe

The probe order would be USB before PHY even though the USB probe
_depended_ on the PHY probe being finished...  :-/  Anyway, probably
I'm just misunderstanding something and someone can tell me how dumb I
am...

I also notice that the ehci_platform_power_off() function we're
actually making PHY commands right before the same commands that turn
off our clocks.  Presumably those commands aren't really so good to do
if the PHY has already been suspended?

Actually, does the PHY suspend from platform_pm_suspend() actually
even do anything?  It doesn't look like it.  It looks as if all the
PHY cares about is init/exit and on/off...  ...and it looks as if the
PHY should be turned off by the EHCI controller at about the same time
it turns off its clocks...

I haven't fully dug, but is there any chance that things are getting
confused between the OTG PHY and the Host PHY?  Maybe when we turn off
the OTG PHY it turns off something that the host PHY needs?


> and the
> clk-480m provided by it was disabled if no module used. However,
> some suspend process related ehci/ohci are base on this clock,
> so we should refer it into ehci/ohci driver to prevent this case.

Though I don't actually have details about the internals of the chip,
it does seem highly likely that the USB block actually uses this clock
for some things, so it doesn't seem insane (to me) to have the USB
controller request that the clock be on.  So, in general, I don't have
lots of objections to including the USB PHY Clock here.

...but I think you have the wrong clock (please correct me if I'm
wrong).  I think you really wanted your input clock to be
"clk_usbphy0_480m", not "clk_usbphy0_480m_src".  Specifically I
believe there is a gate between the clock outputted by the PHY and the
USB Controller itself.  I'm guessing that the gate is only there
between the PHY and the "clk_usbphy_480m" MUX.

As evidence, I have a totally functioning system right now where
"clk_usbphy0_480m_src" is currently gated.

That means really you should be changing your clocks to this (untested):

               clocks = <&cru HCLK_HOST0>, <&cru HCLK_HOST0_ARB>,
                        <&u2phy0>;

...and then you could drop the other two patches in this series.

===

OK, I actually briefly tested my proposed change and it at least seems
to build and boot OK.  You'd have to test it to make sure it makes
your tests pass...

===

So I guess to summarize all the above:

* It seems to me like there's some deeper root cause and your patch
will at most put a band-aid on it.  Seems like digging out the root
cause is a good idea.

* Though I don't believe it solves the root problem, the idea of the
USB Controller holding onto the PHY clock doesn't seem wrong.

* You're holding onto the wrong clock in your patch--you want the one
before the gate (I think).


-Doug