On Mon, Jun 21, 2021 at 07:55:30AM -0700, Matthias Kaehlcke wrote: > On Sat, Jun 19, 2021 at 10:30:22AM +0900, Masahiro Yamada wrote: > > On Sat, Jun 19, 2021 at 2:05 AM Matthias Kaehlcke <mka@xxxxxxxxxxxx> wrote: > > > > > > Hi, > > > > > > I'm adding a new driver and have an issue with Kconfig dependencies > > > that I coulnd't sort out so far. > > > > > > 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 > > > > > > 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]) > > > > > > I read through kconfig-language.rst and experimented a fair bit, > > > but haven't found a working solution. Any advice would be > > > appreciated. > > > > > > Thanks > > > > > > Matthias > > > > > > > > This issue should be discussed in the USB ML, > > That's where it was initially brought up, but it didn't get the attention > of anyone in the position to give advice. Since the issue is more about > kbuild dependencies than USB specifically I brought it up here. The driver > already landed in the USB tree but was reverted due to this issue, I'm > stuck on this problem and really don't want the driver to die on the > finish line. > > A workaround could be to make the driver 'bool' rather than 'tristate', > but I'm not sure if that would be acceptable. > > > but probably 'depends on USB_XHCI_PLATFORM' should be used everywhere instead of > > 'depends on USB_XHCI_PLATFORM'. > > Did you mean 'select USB_XHCI_PLATFORM' rather than 'depends on > USB_XHCI_PLATFORM'? In general that sounds reasonable, since the drivers don't > actually depend on USB_XHCI_PLATFORM from a build perspective, and it's what > some drivers actually do. However it doesn't fix the problem, apparently a > 'select X' from CONFIG_Y still results in CONFIG_X being 'y' if CONFIG_Y is > 'y' (see the USB_DWC3 case above). After some more experimentation it looks like the opposite fixes the conflict, i.e. changing all instances of 'select USB_XHCI_PLATFORM' to 'depends on USB_XHCI_PLATFORM'. That's also in line with the recommendation to limit the use of 'select' to certain use cases: select should be used with care. select will force a symbol to a value without visiting the dependencies. By abusing select you are able to select a symbol FOO even if FOO depends on BAR that is not set. In general use select only for non-visible symbols (no prompts anywhere) and for symbols with no dependencies. That will limit the usefulness but on the other hand avoid the illegal configurations all over. https://www.kernel.org/doc/html/latest/kbuild/kconfig-language.html
