drm/amd/display: Get backlight from PWM if DMCU is not initialized

On Carrizo/Stoney systems we set backlight through panel_cntl, i.e.
directly via the PWM registers, if DMCU is not initialized. We
always read it back through ABM registers which leads to a
mismatch and forces atomic_commit to program the backlight
each time.

Instead make sure we use the same logic for backlight readback,
i.e. read it from panel_cntl if DMCU is not initialized.

We also need to remove some extraneous and incorrect calculations
at the end of dce_get_16_bit_backlight_from_pwm.

Bug: https://gitlab.freedesktop.org/drm/amd/-/issues/1666
Cc: [email protected]

Reviewed-by: Josip Pavic <[email protected]>
Acked-by: Mikita Lipski <[email protected]>
Signed-off-by: Harry Wentland <[email protected]>
Tested-by: Daniel Wheeler <[email protected]>
Signed-off-by: Alex Deucher <[email protected]>

0 files changed, 0 insertions, 0 deletions