RE: How to detect Cherry Trail vs Brasswell inside the kernel ?

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Would it be possible to ask the vendor to remove INT0002 device from the
firmware?

Even if all vendors would issue BIOs updates for this for all models
(which they won't) then we still cannot count on users installing those
BIOS updates. Because of this relying on a BIOS update is almost never the
right answer.

(Note I guess there might be some extreme circumstans / some corner case where
things are so broken that we will tell users to just upgrade their BIOS)

It wasn't clear to me if this inquiry was for release or pre-release hardware.
If it's pre-release hardware this is actually quite preferable in my opinion.

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2. Deal with non functional /sys/class/backlight/acpi_video[0-7] devices
showing up on BYT/CHT based media-boxes / hdmi-sticks. These devices do
not have a LCD panel, so there will be no "native" backlight driver causing
drivers/acpi/video-detect.c to select acpi_backlight_video as backlight-

type.

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drivers/acpi/acpi-video.c tries to avoid registering non-functional
/sys/class/backlight/acpi_video devices in cases like this, but that

depends

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on a DMI chassis-type check (to avoid suppressing the backlight interface
on laptops where we likely do want it) and many of these media-boxes /
hdmi-sticks are derived from BYT/CHT tablet designs and often the DMI
chassis type still says "Tablet". Actual Cherry Trail devices with a LCD
panel always use the native intel_backlight interface, but I guess some
Braswell based devices might use the acpi_video interface.

Maybe a function to look at specifically the DMI chassis type of "Tablet"

and

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check for the lack of an internal LCD panel.  That seems like detecting that
combination shouldn't ever try to run this code.

The issue is that we cannot detect the presence of a LCD panel from the
ACPI-video code. That is done by the i915 driver (on these devices) and
we really don't want any (more) dependencies between the acpi-video code
and the i915 code as those are very hard to manage wrt things like the
probing order. Also the ACPI-video code is supposed to be platform and
even architecture independent.

Regards,

Hans