linux-next: Tree for Sep 11 (drivers/gpu/drm/i915/display/intel_backlight.o)

[Randy Dunlap]

Hi Jani,

On 9/12/23 07:52, Randy Dunlap wrote:
> 
> 
> On 9/12/23 00:47, Jani Nikula wrote:
>> On Mon, 11 Sep 2023, Randy Dunlap <rdunlap at infradead.org> wrote:
>>> On 9/10/23 19:11, Stephen Rothwell wrote:
>>>> Hi all,
>>>>
>>>> Please do *not* include material destined for v6.7 in your linux-next
>>>> included branches until *after* v6.6-rc1 has been released.  Also,
>>>> do *not* rebase your linu-next included branches onto v6.5.
>>>>
>>>> Changes since 20230908:
>>>>
>>>> Non-merge commits (relative to Linus' tree): 643
>>>>  614 files changed, 227990 insertions(+), 9502 deletions(-)
>>>>
>>>> ----------------------------------------------------------------------------
>>>
>>> on x86_64:
>>>
>>> # CONFIG_ACPI is not set
>>> CONFIG_DRM_I915=y
>>> CONFIG_BACKLIGHT_CLASS_DEVICE=m
>>>
>>> I915 selects BACKLIGHT_CLASS_DEVICE if ACPI is set.
>>>
>>> ld: drivers/gpu/drm/i915/display/intel_backlight.o: in function `intel_backlight_device_register':
>>> intel_backlight.c:(.text+0x4988): undefined reference to `backlight_device_get_by_name'
>>> ld: intel_backlight.c:(.text+0x4a1b): undefined reference to `backlight_device_register'
>>> ld: drivers/gpu/drm/i915/display/intel_backlight.o: in function `intel_backlight_device_unregister':
>>> intel_backlight.c:(.text+0x4b56): undefined reference to `backlight_device_unregister'
>>
>> This comes up periodically. The fix is for i915 to depend on backlight,
>> but it's not possible to fix just i915, as it'll lead to circular deps
>> unless *all* select backlight is switched to depend on backlight.
>>
>> I've gone through it once [1], and not keen on doing it again unless
>> there's buy-in.
>>
>> IS_REACHABLE() is often suggested as a workaround, but I think it's just
>> plain wrong. i915=y backlight=m is not a configuration that makes
>> sense. Kernel configuration is hard enough, there's no point in allowing
>> dumb configs that just silently don't work.
>>
> 
> Yes, IS_REACHABLE() is just fugly nonsense.
> 
> Thanks for the reminder of your attempt(s).
> 
>>
>> BR,
>> Jani.
>>
>>
>> [1] https://lore.kernel.org/r/1413580403-16225-1-git-send-email-jani.nikula@intel.com

I did a partial patch series (eliminated the I915 problems with 9 patches,
without build testing -- only kconfig testing -- so more changes may be
needed), then I looked at your patch [1] above.

I like it but even if Tomi and Daniel didn't have problems with it,
I am concerned that it would cause problems with existing working .config files.

Still, something should be done about the mixed usage of select and depends on
for BACKLIGHT_CLASS_DEVICE (et al).

thanks.
-- 
~Randy