I have an aspire 7715 and I had the same problem.
also that work around worked for me.
another note.
adding acpi_backlight=video to the kernel command line makes the system aware of when the brightness changes, it still can't change it in software.
acpi_backlight=vender the backlight keys still work but the os doesn't seem to see when you change the brightness.
also software brightness control works in windows, for whatever that is worth.
I have an aspire 7715 and I had the same problem.
also that work around worked for me.
another note. video to the kernel command line makes the system aware of when the brightness changes, it still can't change it in software. vender the backlight keys still work but the os doesn't seem to see when you change the brightness.
adding acpi_backlight=
acpi_backlight=
also software brightness control works in windows, for whatever that is worth.