In most cases, the default values of DSI PHY tuning registers should be
sufficient as they are fully optimized. However, in some cases where
extreme board parasitics cause the eye shape to degrade, the override
bits can be used to improve the signal quality.

The general guidelines for DSI PHY tuning include:
- High and moderate data rates may benefit from the drive strength and
  drive level tuning.
- Drive strength tuning will affect the output impedance and may be used
  for matching optimization.
- Drive level tuning will affect the output levels without affecting the
  impedance.

The clock and data lanes have a calibration circuitry feature. The drive
strength tuning can be done by adjusting rescode offset for hstop/hsbot,
and the drive level tuning can be done by adjusting the LDO output level
for the HSTX drive.
Signed-off-by: Rajeev Nandan <quic_rajeevny@quicinc.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/1643573719-32095-2-git-send-email-quic_rajeevny@quicinc.comSigned-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>