[0/4] Stop accessing display TIMESTAMP_OVERRIDE in GT code

Message

Matt Roper Feb. 21, 2025, 12:38 a.m. UTC

When determining the GT command streamer frequency, there are two
approaches used by i915 and Xe:

 - Derive the CS frequency from the crystal clock frequency register (or
   a per-platform hardcoded value).  This is supposed to be the method
   usually used (and the only method supported at all for Xe2 and later
   hardware).

 - Set the CS frequency to exactly the display refclk frequency.  This
   is supposedly a rare case, and is used only when a setting in
   CTC_MODE[0] indicates we should use this approach.

There's little/no documentation in the hardware specs about these
approaches (i.e., the display refclk approach is simply referred to as
"Broadwell Divide Logic" with no further explanation).  It seems most of
the logic here was originally inherited from the Windows driver a long
time ago and we've just been carrying it forward ever since.

Currently the second approach (use of display reference clock) is
accomplished by reading a display debug register (TIMESTAMP_OVERRIDE).
Given that the display code already has more straightforward logic for
determining display reference clock (either from strap registers, or
from a per-platform constant in cases where there's only one possible
value), it makes sense to just call the display code to get the
frequency rather than doing direct access to the display hardware inside
the GT driver.


Matt Roper (4):
  drm/i915/display: Make refclk fetching logic reusable
  drm/i915/gt: Replace TIMESTAMP_OVERRIDE readout
  drm/xe: Drop usage of TIMESTAMP_OVERRIDE
  drm/xe/sriov: Drop TIMESTAMP_OVERRIDE from Xe2 runtime regs

 drivers/gpu/drm/i915/display/intel_cdclk.c    | 44 ++++++++++++-------
 drivers/gpu/drm/i915/display/intel_cdclk.h    |  1 +
 .../gpu/drm/i915/gt/intel_gt_clock_utils.c    | 31 ++++---------
 drivers/gpu/drm/xe/display/xe_display.c       |  6 +++
 drivers/gpu/drm/xe/display/xe_display.h       |  4 ++
 drivers/gpu/drm/xe/xe_gt_clock.c              | 28 ++++--------
 drivers/gpu/drm/xe/xe_gt_sriov_pf_service.c   |  1 -
 7 files changed, 56 insertions(+), 59 deletions(-)