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 ... > > > 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. > > 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.
