We got Backlight Controls! BUT...
salv.prestipino at gmail.com
Fri Oct 28 12:07:10 CEST 2016
Hi all, I'm the same person that last time have wrote with the name Okusho,
set of patches from Shobhit Kumar, and a fix from Viric, that I have ported
on kernel 4.8, we can enable pwm-lpss backlight control on our device! (see
the huge but below). with the backlight control the battery life of our
device is highly enhanced, I don't see drawbacks on my system.
BUT for make this set of patches work, I had to modify my DSDT table, to
enable pwm-lpss probe. In my system the probe is blocked from a DSDT
variable, OSSL. So since DSDT table edit is not a portable solution we have
to understand how to initialize correctly the OSSL variable.
what I know on this variable is that is initialized at boot time, end. I
know only this, in interent I haven't found any information, there are only
people that have removed completely the OSSL variable from their DSDT
table, but this is not a solution for me.
I have some hypothesis on this variable, in the bios, in the option secure
boot i've read something like "... in this system openssl is used for
enable secure boot..." so i think that OSSL=OpenSSL, and I think that at
boot time either if the secure boot option is active or not, the system
checks if in the efi partition is present the secure boot key (I have
formatted my efi partition, so I don't have the secure boot key) if is
present, the OSSL variable is initialized. This system is understandable,
if the system don't have the secure boot key, some hardware components are
disabled (in fact the OSSL variable don't enable only the pwm-lpss). I
think that there are two posible condition to enable the OSSL variable:
1)in the system there is the original efi partition, not formatated, that
have the secure boot key
2) if you enable the secure boot option in the bios, you are anyway able to
boot in Ubuntu.
I think that condition two is the right one, but I don't know if condition
2 is equivalent to 1, maybe someone of you can test this patches and see if
they enable the backlight control, without DSDT modification, and report
its efi secure boot situation, and if condition 2 is verified.
to test it, you can use the patchs above, or maybe my kernel at
kernel contains the sound patches too, i've read that Paul Mansfield have
lost his speakers (I'm sorry) so BE CAREFUL), let's try to understand how
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