Intel GMA: Backlight brightness driver

[Patrick Rudolph]

Dear coreboot users,
The following commit adds Mailbox 3 support for improved panel back-
light brigthness control on Intel GMA platforms.

It fixes the problem with 100% brightness on S3 resume.

Please test and review https://review.coreboot.org/#/c/coreboot/+/27711
/

Regards,
Patrick

[Alexander Couzens]

Hi Patrick,

thanks for your work.
Are there any documentation or description what Mailbox 3 support is?
Where it come from?

Best,
lynxis