[Bug 96571] [CHV] Backlight init fails on Surface 3 if module load order is wrong

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=96571

--- Comment #63 from Hans de Goede <jwrdegoede at fedoraproject.org> ---
Hi All,

I was not aware that this bug existed, @youling257 pointed me here.

Note that the generic issue from this bug, when using a generic kernel with
most drivers as modules, has been fixed long ago (January 2017)

I wrote a patch which makes the pwm-core load the module when the pwm device is
being looked-up by the i915 driver:

https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=b526a314263ea217b8fa9758dca5dc245fd49997

This does require that at least the i915 driver is a module, so that it is no
initialized before request_module is possible. This allows the pwm driver
itself to also be a module. Note that if the pwm driver is a module and the
i915 driver is loaded by the initrd; then the pwm-driver and all of its
dependencies must also be in the initrd. I've patches dracut to get this right
a long time ago, I do not know about other initrd generating tools.

As for having i915 / everything builtin that simply is not possible with the
current state of things. IIRC having i915 builtin has other issues too (at
least with Fedora we hit other issues when building in the drm/kms drivers).

So IMHO this bug can be closed now, as the original issue is solved as long as
the i195 driver is a module and building it in is simply not a supportable case
on this hardware.

Regards,

Hans

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