On Mon, Jun 21, 2021 at 01:26:01PM +0200, Enrico Weigelt, metux IT consult wrote:

On 18.06.21 19:05, Matthias Kaehlcke wrote:

Hi,


Cc'ing to linux-usb ...

quoted

Patch https://lore.kernel.org/patchwork/patch/1444212/ adds the new
onboard_usb_hub driver which exports two functions,
onboard_hub_create_pdevs() and onboard_hub_destroy_pdevs(). It also
provides stubs for these functions which are used when the driver
is not selected (CONFIG_USB_ONBOARD_HUB=n).

The new exported functions are called by the xhci-plat driver
(https://lore.kernel.org/patchwork/patch/1444215/). Since xhci-plat
now depends on symbols from the onboard_hub_driver the following
dependency was added to its Kconfig entry:

  config USB_XHCI_PLATFORM
    tristate "Generic xHCI driver for a platform device"
    select USB_XHCI_RCAR if ARCH_RENESAS
 +  depends on USB_ONBOARD_HUB || !USB_ONBOARD_HUB

What exactly do you intent to archieve with this ?

X or !X = 1, isn't it ?

Why should something depend on something present or absent ?

Is that depends on ... statement necessary at all ?

I know, it's confusing, I had the same reaction when I first saw that
construct.

Effectively USB_XHCI_PLATFORM can be built without USB_ONBOARD_HUB.
However if USB_ONBOARD_HUB is built as a module then USB_XHCI_PLATFORM
should also be built as a module, which is what the above statement
achieves, unless there are conflicting dependencies.

The same construct is used for CONFIG_USB_XHCI_PCI.

quoted

This generally seems to work, however when USB_XHCI_PLATFORM is
forced to be builtin by another driver that depends on it (e.g.
USB_DWC3) it is still possible to build the onboard_hub driver
as a module, which results in unresolved symbols:

aarch64-linux-gnu-ld: drivers/usb/host/xhci-plat.o: in function
`xhci_plat_remove':
drivers/usb/host/xhci-plat.c:427: undefined reference to
`onboard_hub_destroy_pdevs'
drivers/usb/host/xhci-plat.c:427:(.text+0x82c): relocation truncated
to fit: R_AARCH64_CALL26 against undefined symbol
`onboard_hub_destroy_pdevs'
aarch64-linux-gnu-ld: drivers/usb/host/xhci-plat.o: in function
`xhci_plat_probe':
drivers/usb/host/xhci-plat.c:379: undefined reference to
`onboard_hub_create_pdevs'
drivers/usb/host/xhci-plat.c:379:(.text+0x131c): relocation truncated
to fit: R_AARCH64_CALL26 against undefined symbol
`onboard_hub_create_pdevs'

Kconfig generates the following warning with this configuration:

WARNING: unmet direct dependencies detected for USB_XHCI_PLATFORM
  Depends on [m]: USB_SUPPORT [=y] && USB [=y] && USB_XHCI_HCD [=y] && (USB_ONBOARD_HUB [=m] || !USB_ONBOARD_HUB [=m])
  Selected by [y]:
  - USB_DWC3 [=y] && USB_SUPPORT [=y] && (USB [=y] || USB_GADGET [=y]) && HAS_DMA [=y] && USB_XHCI_HCD [=y]
  Selected by [m]:
  - USB_CDNS_SUPPORT [=m] && USB_SUPPORT [=y] && (USB [=y] || USB_GADGET [=y]) && HAS_DMA [=y] && USB_XHCI_HCD [=y]
  - USB_BRCMSTB [=m] && USB_SUPPORT [=y] && USB [=y] && (ARCH_BRCMSTB [=y] && PHY_BRCM_USB [=m] || COMPILE_TEST [=y]) && USB_XHCI_HCD [=y]
  - USB_XHCI_MVEBU [=m] && USB_SUPPORT [=y] && USB [=y] && USB_XHCI_HCD [=y] && HAS_IOMEM [=y] && (ARCH_MVEBU [=y] || COMPILE_TEST [=y])

It seems that Kconfig is confused by trying to enforce contradicting
dependencies.

yep, the purpose of my post was to sort that out :)

Now for your driver:

TBH I don't think this is the right thread to discuss the driver, this
should be done on the corresponding patches.

If I understand it correctly, you've got a topology like this:


root hub -+--> 2ndary hub #0 -+--> usb-dev #0
          |                   \--> usb-dev #1
          |                     ..
          \--> 2ndary hub #1 -+--> usb-dev #3
                              \--> usb-dev #4


And in order to get usb-dev #foo running, you need the corresponding
hub on its path powered (which in turn is platform specific).

Correct ?

yep

So, why not reflecting exactly this topology in the device tree ?
In that case, the power management *IMHO* could pretty automatically
(assuming you've implemented the corresponding pm functions on the
2ndary hub driver).

Okay, that could become a bit tricky when the usb-dev's are
automatically enumerated on the root hub and would need to be
reparented somehow ... @usb folks: it that possible ?

AFAIK the USB devices (including the secondary hubs) are all automatically
enumerated, the representation in the device tree is optional in the vast
majority of cases, so it's a bit of a chicken-egg problem.

Another option could be implementing this as a regulator that the
individual usb devices will be attached to. Not completely semantically
correct (since a hub isn't exactly a regulator :o), but should at least
do the job: the regulator will be switched on when the device is used
and can be switched off when it isn't used anymore.

IMO the representation as a hub is preferable, also initialization might
be more complex than switching on a single regulator (e.g. multiple
regulators, GPIOs, clocks, ...)

The cleanest approach, IMHO, might be adding an hub subsys, somewhat
similar to the existing phy subsys. I can imagine similar cases with
other interfaces, not just USB only, at least certainly not specific
to xhci.

Or could existing phy subsys already be sufficient for that ?

I'll leave that to the USB maintainers, who seem to be happy/ok with
the current approach. There was discussion about other solutions,
including a revival of the pwrseq series
(https://lore.kernel.org/patchwork/project/lkml/list/?series=314989&state=%2A&archive=both),
which was discarded.

In any case the current solution isn't specific to xHCI. At this point
only xhci-plat is supported, however it could be extended to other
USB controllers if needed.