Kconfig DRM_USB/DRM_UDL, and select vs. depends, and causing Tegra USB to be disabled

DISCUSSION Stephen Warren 2 participants 3 messages Sep 4, 2012 2 messages not in the archive Tegra architecture support

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Stephen Warren

author

2012-09-04 19:19 UTC #0 lore raw

With respect to the following commits:

df0b344 drm/usb: select USB_SUPPORT in Kconfig
8f057d7 gpu/mfd/usb: Fix USB randconfig problems

... which end up with the following in next-20120904:

config DRM_USB
depends on DRM
depends on USB_ARCH_HAS_HCD
select USB
select USB_SUPPORT

config DRM_UDL
depends on DRM && EXPERIMENTAL
depends on USB_ARCH_HAS_HCD
select DRM_USB

Surely this is backwards; these should be dependencies, not selects? In other words:

config DRM_USB

        depends on DRM && USB

config DRM_UDL

        depends on DRM && EXPERIMENTAL && USB
        select DRM_USB

or perhaps:

config DRM_USB

        depends on DRM && USB

config DRM_UDL

        depends on DRM && EXPERIMENTAL && DRM_USB

The problem here is that currently, the dependency logic for USB:

config USB
depends on USB_ARCH_HAS_HCD

... is duplicated into each of DRM_USB and DRM_UDL, thus requiring both of those to be edited should the dependencies for USB ever change.

The current state of the code also causes some strange problem with ARM's tegra_defconfig, whereby running "make tegra_defconfig" will result in USB support fully enabled in .config as expected, yet subsequently running "make oldconfig" will cause all USB support to be removed from .config. For some reason, the above DRM logic is causing CONFIG_USB_ARCH_HAS_HCD not to be selected (perhaps it isn't evaluated because USB is selected, so there's no need to evaluate USB's dependencies?). Arguably, this is a deficiency in Tegra's Kconfig, in that it probably should say:

select USB_ARCH_HAS_EHCI

not:

select USB_ARCH_HAS_EHCI if USB_SUPPORT

... but it has contained the latter for quite some time, and it's always worked before somehow.
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Guenter Roeck

2012-09-04 20:00 UTC #2 lore raw

Quoted 36 lines · Stephen Warren

With respect to the following commits:
df0b344 drm/usb: select USB_SUPPORT in Kconfig
8f057d7 gpu/mfd/usb: Fix USB randconfig problems
... which end up with the following in next-20120904:
config DRM_USB
depends on DRM
depends on USB_ARCH_HAS_HCD
select USB
select USB_SUPPORT
config DRM_UDL
depends on DRM && EXPERIMENTAL
depends on USB_ARCH_HAS_HCD
select DRM_USB
Surely this is backwards; these should be dependencies, not selects? In other words:
config DRM_USB
        depends on DRM && USB
config DRM_UDL
        depends on DRM && EXPERIMENTAL && USB
        select DRM_USB
or perhaps:
config DRM_USB
        depends on DRM && USB
config DRM_UDL
        depends on DRM && EXPERIMENTAL && DRM_USB

Quoted 8 lines

The problem here is that currently, the dependency logic for USB:
config USB
depends on USB_ARCH_HAS_HCD
... is duplicated into each of DRM_USB and DRM_UDL, thus requiring both of those to be edited should the dependencies for USB ever change.

This should be fixed with in https://patchwork.kernel.org/patch/1373371/ (drm:
udl: usb: Fix recursive Kconfig dependency), which should make it into the next iteration of linux-next.

Guenter
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Stephen Warren

author

2012-09-04 21:01 UTC #4 lore raw

Quoted 42 lines · Guenter Roeck

Quoted 41 lines · Stephen Warren
With respect to the following commits:
df0b344 drm/usb: select USB_SUPPORT in Kconfig
8f057d7 gpu/mfd/usb: Fix USB randconfig problems
... which end up with the following in next-20120904:
config DRM_USB
depends on DRM
depends on USB_ARCH_HAS_HCD
select USB
select USB_SUPPORT
config DRM_UDL
depends on DRM && EXPERIMENTAL
depends on USB_ARCH_HAS_HCD
select DRM_USB
Surely this is backwards; these should be dependencies, not selects? In other words:
config DRM_USB
        depends on DRM && USB
config DRM_UDL
        depends on DRM && EXPERIMENTAL && USB
        select DRM_USB
or perhaps:
config DRM_USB
        depends on DRM && USB
config DRM_UDL
        depends on DRM && EXPERIMENTAL && DRM_USB
The problem here is that currently, the dependency logic for USB:
config USB
depends on USB_ARCH_HAS_HCD

Quoted 6 lines

Quoted 2 lines
... is duplicated into each of DRM_USB and DRM_UDL, thus requiring both of those to be edited should the dependencies for USB ever change.
This should be fixed with in https://patchwork.kernel.org/patch/1373371/ (drm:
udl: usb: Fix recursive Kconfig dependency), which should make it into the next iteration of linux-next.

Yes, this does appear to solve all the problems for me. Thanks.

I still tend to believe that drivers should probably depend on things rather than select them, but given the common precedent for "select USB" that exists here, others clearly don't agree!

Sorry; accidentally sent the email too early last time:-(