drm/i915/cx0: Check and increase msgbus timeout threshold

drm/i915/cx0: Check and increase msgbus timeout threshold

We have experienced timeout issues when going through the sequence to
access C20 SRAM registers. Experimentation showed that bumping the
message bus timer threshold helped on getting display Type-C connection
on the C20 PHY to work.

While the timeout is still under investigation with the HW team, having
logic to allow forward progress (with the proper warnings) seems useful.
Thus, let's bump the threshold when a timeout is detected.

The bumped value of 0x200 pclk cycles was somewhat arbitrary - 2x the
default value. That value was successfully tested on real hardware that
was displaying timeouts otherwise.

v2:
  - Reword commit message to indicate that access to C20 SRAM registers
    is not direct. (Radhakrishna)
  - Prefer not to use REG_FIELD_PREP() in intel_cx0_phy.c.
    (Radhakrishna)
  - Simplify intel_cx0_bus_check_and_bump_timer() to use a fixed bumped
    value instead of progressively increasing the threshold. (Mika)

BSpec: 65156
Cc: Radhakrishna Sripada <radhakrishna.sripada@intel.com>
Cc: Mika Kahola <mika.kahola@intel.com>
Signed-off-by: Gustavo Sousa <gustavo.sousa@intel.com>
Reviewed-by: Mika Kahola <mika.kahola@intel.com>
Signed-off-by: Matt Roper <matthew.d.roper@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230830121524.15101-1-gustavo.sousa@intel.com