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drm/xe: Add debugfs knob to control GPGPU preemption granularity

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Introduce a per-GT debugfs knob, 'gpgpu_preemption_level', to allow
overriding the GPGPU preemption level on a per-context basis for newly
created LRCs.
Add an RTP rule to enable per-context control via FF_SLICE_CS_CHICKEN1,
allowing the preemption level to be programmed directly into the LRC
image at CTX_CS_CHICKEN1 during context initialization.

v9:
  - Move the per-context/GT-scoped behavior description from the enum
    kerneldoc to the gpgpu_preemption_level member kerneldoc, and drop
    the kzalloc zero-initialization note. (Gustavo)

v8:
  - Encapsulate LRC preemption programming into
    xe_lrc_set_gpgpu_preemption_level() (Gustavo)
  - Add xe_gt_WARN and early return for unexpected preemption level values
    to prevent invalid CS_CHICKEN1 programming. (Gustavo)
  - Change -EPERM to -EINVAL for MTP fused off check (Gustavo)
  - Combine FF_SLICE_CS_CHICKEN1 RTP rule using OR macro (Gustavo)

v7:
  - Restrict XEHP_FUSE4 read to Xe2+ primary GTs to prevent invalid
    Media GT accesses and SR-IOV warnings. (Sashiko)

v6:
  - Add missing xe_gt_printk.h include to fix compilation failure.

v5:
  - Use correct offset for CTX_CS_CHICKEN1. (Matt)
  - Restrict to the RCS engine. (Matt)
  - Drop LRC layout table modifications; dummy layouts do not need late
    context registers. (Matt)
  - Stash WMTP fuse state at boot to remove pm/forcewake from debugfs.
    (Matt)
  - Rename debugfs knob to 'gpgpu_preemption_level'. (Matt)
  - Use simple_write_to_buffer() and remove unnecessary READ_ONCE/
    WRITE_ONCE macros. (Matt)
  - Do not restrict debugfs visibility for SR-IOV VFs. (Matt)

v4
  - Fix incorrect NOP padding in the RCS context layout. (Sashiko)

v3:
  - Wrapped XEHP_FUSE4 forcewake read with xe_pm_runtime_get/put to
    prevent PCIe aborts/timeouts when the GPU is in D3hot/D3cold. (sashiko)
  - Fixed NOP macro truncation by splitting padding offsets larger than
    0x7f into multiple NOPs, ensuring correct context layout. (sashiko)
  - Converted CTX_CS_CHICKEN1 initialization to a read-modify-write
    sequence to avoid overwriting golden context mask bits. (sashiko)
  - Removed the FF_SLICE_CS_CHICKEN1 workaround for CCS engines, as
    compute engines lack this 3D fixed-function register, which was
    causing GuC "illegal register" panics on initialization.

v2:
  - Dropped the WA BB/MI_LRI path; per Bspec, CS_CHICKEN1 is context
    save/restore state at DW 0x00E2, so we map CTX_CS_CHICKEN1 and program
    it directly in LRC init via xe_lrc_write_ctx_reg(). (Matt)
  - Split Xe2 CCS context offsets into a dedicated xe2_ccs_offsets array
    to map CS_CHICKEN1 without polluting other XCS engines.
  - Converted the debugfs interface from a binary boolean to a
    multi-option string knob ("default", "mid-thread", "thread-group",
    "command"). (Gustavo)
  - Restricted file creation to the Physical Function
    (!IS_SRIOV_VF). (Gustavo)
  - Added kernel tainting (TAINT_USER) when deviating from
    defaults. (Gustavo)
  - Added power-safe hardware fuse check (FUSE4 register 0x9114[20],
    CFEG_WMTP_DISABLE) before allowing MTP selection. (Matt)

Signed-off-by: Varun Gupta <varun.gupta@intel.com>
Reviewed-by: Gustavo Sousa <gustavo.sousa@intel.com>
Reviewed-by: Matt Roper <matthew.d.roper@intel.com>
Link: https://patch.msgid.link/20260827072106.1138741-2-varun.gupta@intel.com
Signed-off-by: Matt Roper <matthew.d.roper@intel.com>
This commit is contained in:
Varun Gupta 2026-08-27 12:51:07 +05:30 • committed by Matt Roper
commit 6a8789e948
6 changed files with 139 additions and 1 deletions
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