[Bug 82634] [snb] backlight issue on TOSHIBA PORTEGE R830 after suspend/resume

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=82634

--- Comment #33 from Aaron Lu <aaron.lu at intel.com> ---
The acpidump shows that _BCM makes use of SMM code to do the backlight
handling by writing some values to some fixed memory address and then
write a value to IO port 0xB2:

_BCM -> SMBR -> BIOT(arg0, arg1, ..., arg6)

Method (BIOT, 7, Serialized)
{
        IEAX = Arg0
        IEBX = Arg1
        IECX = Arg2
        IEDX = Arg3
        IESI = Arg4
        IEDI = Arg5
        SSMP = Arg6
}

The IEXX are fields defined in an operation region of memory type and
from their names, they seem to be meant to pass their values to the
corresponding registers. And SSMP is defined as:

OperationRegion (SPRT, SystemIO, 0xB2, 0x02)
Field (SPRT, ByteAcc, Lock, Preserve)
{
        SSMP,   8
}

And the final write to it should trigger SMI. The SMM code may do something
magical and I have no idea what would happen there.

Sylvain also said that a LID status change could bring up the backlight, I
suspect that has something to do with intel_lid_notify, perhaps this function
bring up the backlight?

Sylvain,
I'll attach a test patch to disable the register of intel_lid_notify and then
please test if open/close the LID, you can still turn the backlight on, thanks.
You may get a black screen with this test patch, please prepare for that.

If the result is no, then perhaps that means intel_lid_notify has the knowledge
of turning the backlight on and we should use that somewhere in i915 driver to
turn on the backlight during resume?

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