Re: [PATCH v4 0/2] arm: dts: rockchip: rk3399: usb: ehci: Fix EHCI probe in rk3399 to access peripherals by USB 2.

[Xavier Drudis Ferran <xdrudis@tinet.cat>]

arch/arm/dts/rk3399.dtsi has a node

  usb_host0_ehci: usb@fe380000 {
       compatible = "generic-ehci";

with clocks:

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

The first 2 refer to nodes with class UCLASS_CLK, but &u2phy0
has class UCLASS_PHY.

  u2phy0: usb2phy@e450 {
       compatible = "rockchip,rk3399-usb2phy";

Since clk_get_bulk() only looks for devices with UCLASS_CLK,
it fails with -ENODEV and then ehci_usb_probe() aborts.

The consequence is peripherals connected to a USB 2 port (e.g. in a
Rock Pi 4 the white port, nearer the edge) not being detected.
They're detected if CONFIG_USB_OHCI_GENERIC is selected in Kconfig,
because ohci_usb_probe() does not abort when one clk_get_by_index()
fails, but then they work in USB 1 mode,.

rk3399.dtsi comes from linux and the  u2phy0 was added[1] to the clock
list in:

    commit b5d1c57299734f5b54035ef2e61706b83041f20c
    Author: William wu <wulf@rock-chips.com>
    Date:   Wed Dec 21 18:41:05 2016 +0800

    arm64: dts: rockchip: add u2phy clock for ehci and ohci of rk3399

    We found that the suspend process was blocked when it run into
    ehci/ohci module due to clk-480m of usb2-phy was disabled.
    [...]

Suspend concerns don't apply to U-Boot, and the problem with U-Boot
failing to probe EHCI doesn't apply to linux, because in linux
rockchip_usb2phy_clk480m_register makes u2phy0 a proper clock provider
when called by rockchip_usb2phy_probe().

So I can think of a few alternative solutions:

1- Change ehci_usb_probe() to make it more similar to
   ohci_usb_probe(), and survive failure to get one clock. Looks a
   little harder, and I don't know whether it could break something if
   it ignored a clock that was important for something else than
   suspend.

2- Change rk3399.dtsi effecttively reverting the linux commit
   b5d1c57299734f5b54035ef2e61706b83041f20c. This dealigns the .dtsi
   from linux and seems fragile at the next synchronisation.

3- Change the clock list in rk3399-u-boot.dtsi or somewhere else.
   This survives .dts* sync but may survive "too much" and miss some
   change from linux that we might want.

4- Enable CONFIG_USB_OHCI_GENERIC and use the ports in USB 1 mode.
   This would need to be made for all boards using rk3399.  In a
   simple test reading one file from USB storage it gave 769.5 KiB/s
   instead of 20.5 MiB/s with solution 2.

5- Trying to replicate linux and have usb2phy somehow provide a clk,
   or have a separate clock device for usb2phy in addition to the phy
   device.

This series is a second attempt to implement option 5 as Marek Vasut
requested in December 5th.  Options 1 and 3 didn't get through[2,3].

The first patch in the series (identical to v3) just registers usb2phy
as a clock driver (device_bind_driver() didn't work but
device_bind_driver_to_node() did), without any specific operations, so
that ehci-generic.c finds it and is happy. It worked in my tests on a
Rock Pi 4 B+ (rk3399).

Since Marek Vasut objected to an operationless driver[4], the second
patch adds enable and disable operations adapted from linux prepare
and unprepare operations (and round_rate(), which doesn't seem very
useful anyway since it's a fixed clock). Since there're no users of
this clock in u-boot, I can't see any difference in my tests with only
the first patch or both, so I can't be sure it really works if it's
ever needed, but it's hopefully more complete.

Links: [1] https://lkml.kernel.org/lkml/1731551.Q6cHK6n5ZM@phil/T/
       [2] https://patchwork.ozlabs.org/project/uboot/patch/20220701185959.GC1700@begut/#2954536
       [3] https://patchwork.ozlabs.org/project/uboot/patch/Y44+ayJfUlI08ptM@localhost/#3016099
       [4] https://patchwork.ozlabs.org/project/uboot/patch/Y5IWpjYLB4aXMy9o@localhost/#3018135
      
Cc: Simon Glass <sjg@chromium.org>
Cc: Philipp Tomsich <philipp.tomsich@vrull.eu>
Cc: Kever Yang <kever.yang@rock-chips.com>
Cc: Lukasz Majewski <lukma@denx.de>
Cc: Sean Anderson <seanga2@gmail.com>
Cc: Marek Vasut <marex@denx.de>

Signed-off-by: Xavier Drudis Ferran <xdrudis@tinet.cat>
---

   Changes:

   v4: move v3 to one patch in the series and add a second patch
       to add operations to enable disable the usb2phy 480Mhz clock.
       Also, honour clock-output-names for what is worth.

   v3: implement option 5 (bind usb2phy as a clk driver too) instead
       of option 1 (ehci-generic.c tolerates missing clocks).

   v2: implement option 1 (ehci-generic.c tolerates missing clocks)
      instead of option 3 (change dts node to remove the missing
      clock).