sched_ext: Maintain an online cid mask in the scheduler arenagrafted

Schedulers on the default cid mapping treat [0, nr_online_cids) as the
online set and restart on hotplug. Schedulers that install their own mapping
with scx_bpf_cid_override() have no way to learn which cids are online: the
count no longer identifies members and the CPU-form cpumask is unusable from
cid programs. This is an obvious hole in the cid API.

Add scx_bpf_online_cmask(), a kernel-maintained cmask in the scheduler's
arena, allocated alongside the per-CPU scratch masks and populated after the
cid mapping is finalized and before ops.init(), for child schedulers too.
The pointer stays valid through ops.exit() with no reference to take. It is
the arena offset as a void pointer, the same form struct_ops arena arguments
arrive in. The verifier types the void return as a scalar for the program's
arena cast.

The mask follows the SCX hotplug notifications: seeded from cpu_active_mask
and updated before ops.cid_online/offline() runs, so it lags cpu_online_mask
only inside a hotplug transition. Updates walk the scheduler list under the
lock that also serializes unlinking. Reads are live, not atomic snapshots.
Root initialization excludes hotplug.

v2: Reworded the getter kerneldoc (Andrea Righi).

Signed-off-by: Tejun Heo <tj@kernel.org>
Reviewed-by: Andrea Righi <arighi@nvidia.com>

20 files changed, 274 insertions, 0 deletions

diff --git a/Documentation/gpu/intel-display/async-flip.rst b/Documentation/gpu/intel-display/async-flip.rst
new file mode 100644
index 000000000..40f93e885
--- /dev/null
+++ b/Documentation/gpu/intel-display/async-flip.rst
@@ -0,0 +1,8 @@
+.. SPDX-License-Identifier: MIT
+.. Copyright © 2026 Intel Corporation
+
+Asynchronous Page Flip
+======================
+
+.. kernel-doc:: drivers/gpu/drm/i915/display/intel_display.c
+   :doc: asynchronous flip implementation
diff --git a/Documentation/gpu/intel-display/atomic.rst b/Documentation/gpu/intel-display/atomic.rst
new file mode 100644
index 000000000..43a473181
--- /dev/null
+++ b/Documentation/gpu/intel-display/atomic.rst
@@ -0,0 +1,11 @@
+.. SPDX-License-Identifier: MIT
+.. Copyright © 2026 Intel Corporation
+
+Atomic Modeset Support
+======================
+
+.. kernel-doc:: drivers/gpu/drm/i915/display/intel_atomic.c
+   :doc: atomic modeset support
+
+.. kernel-doc:: drivers/gpu/drm/i915/display/intel_atomic.c
+   :internal:
diff --git a/Documentation/gpu/intel-display/audio.rst b/Documentation/gpu/intel-display/audio.rst
new file mode 100644
index 000000000..eef95df75
--- /dev/null
+++ b/Documentation/gpu/intel-display/audio.rst
@@ -0,0 +1,23 @@
+.. SPDX-License-Identifier: MIT
+.. Copyright © 2026 Intel Corporation
+
+High Definition Audio
+=====================
+
+.. kernel-doc:: drivers/gpu/drm/i915/display/intel_audio.c
+   :doc: High Definition Audio over HDMI and Display Port
+
+.. kernel-doc:: drivers/gpu/drm/i915/display/intel_audio.c
+   :internal:
+
+.. kernel-doc:: include/drm/intel/i915_component.h
+   :internal:
+
+Intel HDMI LPE Audio Support
+============================
+
+.. kernel-doc:: drivers/gpu/drm/i915/display/intel_lpe_audio.c
+   :doc: LPE Audio integration for HDMI or DP playback
+
+.. kernel-doc:: drivers/gpu/drm/i915/display/intel_lpe_audio.c
+   :internal:
diff --git a/Documentation/gpu/intel-display/casf.rst b/Documentation/gpu/intel-display/casf.rst
new file mode 100644
index 000000000..406778ccd
--- /dev/null
+++ b/Documentation/gpu/intel-display/casf.rst
@@ -0,0 +1,8 @@
+.. SPDX-License-Identifier: MIT
+.. Copyright © 2026 Intel Corporation
+
+Content Adaptive Sharpness Filter (CASF)
+========================================
+
+.. kernel-doc:: drivers/gpu/drm/i915/display/intel_casf.c
+   :doc: Content Adaptive Sharpness Filter (CASF)
diff --git a/Documentation/gpu/intel-display/cdclk.rst b/Documentation/gpu/intel-display/cdclk.rst
new file mode 100644
index 000000000..a66d623b0
--- /dev/null
+++ b/Documentation/gpu/intel-display/cdclk.rst
@@ -0,0 +1,11 @@
+.. SPDX-License-Identifier: MIT
+.. Copyright © 2026 Intel Corporation
+
+Display clocks
+==============
+
+.. kernel-doc:: drivers/gpu/drm/i915/display/intel_cdclk.c
+   :doc: CDCLK / RAWCLK
+
+.. kernel-doc:: drivers/gpu/drm/i915/display/intel_cdclk.c
+   :internal:
diff --git a/Documentation/gpu/intel-display/cmtg.rst b/Documentation/gpu/intel-display/cmtg.rst
new file mode 100644
index 000000000..04edd0bd1
--- /dev/null
+++ b/Documentation/gpu/intel-display/cmtg.rst
@@ -0,0 +1,8 @@
+.. SPDX-License-Identifier: MIT
+.. Copyright © 2026 Intel Corporation
+
+Common Primary Timing Generator (CMTG)
+======================================
+
+.. kernel-doc:: drivers/gpu/drm/i915/display/intel_cmtg.c
+   :doc: Common Primary Timing Generator (CMTG)
diff --git a/Documentation/gpu/intel-display/dmc.rst b/Documentation/gpu/intel-display/dmc.rst
new file mode 100644
index 000000000..4368da4c7
--- /dev/null
+++ b/Documentation/gpu/intel-display/dmc.rst
@@ -0,0 +1,26 @@
+.. SPDX-License-Identifier: MIT
+.. Copyright © 2026 Intel Corporation
+
+.. _drm/intel-display/dmc:
+
+DMC Firmware Support
+====================
+
+.. kernel-doc:: drivers/gpu/drm/i915/display/intel_dmc.c
+   :doc: DMC Firmware Support
+
+.. kernel-doc:: drivers/gpu/drm/i915/display/intel_dmc.c
+   :internal:
+
+
+DMC Flip Queue
+==============
+
+.. kernel-doc:: drivers/gpu/drm/i915/display/intel_flipq.c
+   :doc: DMC Flip Queue
+
+DMC wakelock support
+====================
+
+.. kernel-doc:: drivers/gpu/drm/i915/display/intel_dmc_wl.c
+   :doc: DMC wakelock support
diff --git a/Documentation/gpu/intel-display/dpio.rst b/Documentation/gpu/intel-display/dpio.rst
new file mode 100644
index 000000000..84d92ac16
--- /dev/null
+++ b/Documentation/gpu/intel-display/dpio.rst
@@ -0,0 +1,8 @@
+.. SPDX-License-Identifier: MIT
+.. Copyright © 2026 Intel Corporation
+
+DPIO
+====
+
+.. kernel-doc:: drivers/gpu/drm/i915/display/intel_dpio_phy.c
+   :doc: DPIO
diff --git a/Documentation/gpu/intel-display/dpll.rst b/Documentation/gpu/intel-display/dpll.rst
new file mode 100644
index 000000000..c750352e0
--- /dev/null
+++ b/Documentation/gpu/intel-display/dpll.rst
@@ -0,0 +1,14 @@
+.. SPDX-License-Identifier: MIT
+.. Copyright © 2026 Intel Corporation
+
+Display PLLs
+============
+
+.. kernel-doc:: drivers/gpu/drm/i915/display/intel_dpll_mgr.c
+   :doc: Display PLLs
+
+.. kernel-doc:: drivers/gpu/drm/i915/display/intel_dpll_mgr.c
+   :internal:
+
+.. kernel-doc:: drivers/gpu/drm/i915/display/intel_dpll_mgr.h
+   :internal:
diff --git a/Documentation/gpu/intel-display/drrs.rst b/Documentation/gpu/intel-display/drrs.rst
new file mode 100644
index 000000000..a5aaba63d
--- /dev/null
+++ b/Documentation/gpu/intel-display/drrs.rst
@@ -0,0 +1,11 @@
+.. SPDX-License-Identifier: MIT
+.. Copyright © 2026 Intel Corporation
+
+Display Refresh Rate Switching (DRRS)
+=====================================
+
+.. kernel-doc:: drivers/gpu/drm/i915/display/intel_drrs.c
+   :doc: Display Refresh Rate Switching (DRRS)
+
+.. kernel-doc:: drivers/gpu/drm/i915/display/intel_drrs.c
+   :internal:
diff --git a/Documentation/gpu/intel-display/dsb.rst b/Documentation/gpu/intel-display/dsb.rst
new file mode 100644
index 000000000..857aca599
--- /dev/null
+++ b/Documentation/gpu/intel-display/dsb.rst
@@ -0,0 +1,11 @@
+.. SPDX-License-Identifier: MIT
+.. Copyright © 2026 Intel Corporation
+
+Display State Buffer
+====================
+
+.. kernel-doc:: drivers/gpu/drm/i915/display/intel_dsb.c
+   :doc: DSB
+
+.. kernel-doc:: drivers/gpu/drm/i915/display/intel_dsb.c
+   :internal:
diff --git a/Documentation/gpu/intel-display/fbc.rst b/Documentation/gpu/intel-display/fbc.rst
new file mode 100644
index 000000000..de9e19021
--- /dev/null
+++ b/Documentation/gpu/intel-display/fbc.rst
@@ -0,0 +1,11 @@
+.. SPDX-License-Identifier: MIT
+.. Copyright © 2026 Intel Corporation
+
+Frame Buffer Compression (FBC)
+==============================
+
+.. kernel-doc:: drivers/gpu/drm/i915/display/intel_fbc.c
+   :doc: Frame Buffer Compression (FBC)
+
+.. kernel-doc:: drivers/gpu/drm/i915/display/intel_fbc.c
+   :internal:
diff --git a/Documentation/gpu/intel-display/fifo-underrun.rst b/Documentation/gpu/intel-display/fifo-underrun.rst
new file mode 100644
index 000000000..5d8f01921
--- /dev/null
+++ b/Documentation/gpu/intel-display/fifo-underrun.rst
@@ -0,0 +1,11 @@
+.. SPDX-License-Identifier: MIT
+.. Copyright © 2026 Intel Corporation
+
+Display FIFO Underrun Reporting
+===============================
+
+.. kernel-doc:: drivers/gpu/drm/i915/display/intel_fifo_underrun.c
+   :doc: fifo underrun handling
+
+.. kernel-doc:: drivers/gpu/drm/i915/display/intel_fifo_underrun.c
+   :internal:
diff --git a/Documentation/gpu/intel-display/frontbuffer.rst b/Documentation/gpu/intel-display/frontbuffer.rst
new file mode 100644
index 000000000..7ae38e082
--- /dev/null
+++ b/Documentation/gpu/intel-display/frontbuffer.rst
@@ -0,0 +1,14 @@
+.. SPDX-License-Identifier: MIT
+.. Copyright © 2026 Intel Corporation
+
+Frontbuffer Tracking
+====================
+
+.. kernel-doc:: drivers/gpu/drm/i915/display/intel_frontbuffer.c
+   :doc: frontbuffer tracking
+
+.. kernel-doc:: drivers/gpu/drm/i915/display/intel_frontbuffer.h
+   :internal:
+
+.. kernel-doc:: drivers/gpu/drm/i915/display/intel_frontbuffer.c
+   :internal:
diff --git a/Documentation/gpu/intel-display/hotplug.rst b/Documentation/gpu/intel-display/hotplug.rst
new file mode 100644
index 000000000..f33bc0087
--- /dev/null
+++ b/Documentation/gpu/intel-display/hotplug.rst
@@ -0,0 +1,11 @@
+.. SPDX-License-Identifier: MIT
+.. Copyright © 2026 Intel Corporation
+
+Hotplug
+=======
+
+.. kernel-doc:: drivers/gpu/drm/i915/display/intel_hotplug.c
+   :doc: Hotplug
+
+.. kernel-doc:: drivers/gpu/drm/i915/display/intel_hotplug.c
+   :internal:
diff --git a/Documentation/gpu/intel-display/index.rst b/Documentation/gpu/intel-display/index.rst
new file mode 100644
index 000000000..01c3d1e57
--- /dev/null
+++ b/Documentation/gpu/intel-display/index.rst
@@ -0,0 +1,44 @@
+.. SPDX-License-Identifier: MIT
+.. Copyright © 2026 Intel Corporation
+
+.. _drm/intel-display:
+
+====================
+Intel Display Driver
+====================
+
+The Intel display driver provides the display, or :ref:`drm-kms`, support for
+both the :ref:`drm/xe <drm/xe>` and :ref:`drm/i915 <drm/i915>` Intel GPU
+drivers.
+
+The source code currently resides under ``drivers/gpu/drm/i915/display`` due to
+historical reasons, and it's compiled separately into both drm/xe and drm/i915
+kernel modules.
+
+The drm/xe and drm/i915 drivers are the "core" or "parent" drivers for display,
+as they initialize and own the drm device, and pass that on to the display
+driver. The display driver isn't an independent driver in that sense.
+
+.. toctree::
+   :maxdepth: 1
+   :caption: Detailed display topics
+
+   async-flip
+   atomic
+   audio
+   casf
+   cdclk
+   cmtg
+   dmc
+   dpio
+   dpll
+   drrs
+   dsb
+   fbc
+   fifo-underrun
+   frontbuffer
+   hotplug
+   plane
+   psr
+   snps-phy
+   vbt
diff --git a/Documentation/gpu/intel-display/plane.rst b/Documentation/gpu/intel-display/plane.rst
new file mode 100644
index 000000000..59932a820
--- /dev/null
+++ b/Documentation/gpu/intel-display/plane.rst
@@ -0,0 +1,11 @@
+.. SPDX-License-Identifier: MIT
+.. Copyright © 2026 Intel Corporation
+
+Atomic Plane Helpers
+====================
+
+.. kernel-doc:: drivers/gpu/drm/i915/display/intel_plane.c
+   :doc: atomic plane helpers
+
+.. kernel-doc:: drivers/gpu/drm/i915/display/intel_plane.c
+   :internal:
diff --git a/Documentation/gpu/intel-display/psr.rst b/Documentation/gpu/intel-display/psr.rst
new file mode 100644
index 000000000..63e56abcd
--- /dev/null
+++ b/Documentation/gpu/intel-display/psr.rst
@@ -0,0 +1,11 @@
+.. SPDX-License-Identifier: MIT
+.. Copyright © 2026 Intel Corporation
+
+Panel Self Refresh PSR (PSR/SRD)
+================================
+
+.. kernel-doc:: drivers/gpu/drm/i915/display/intel_psr.c
+   :doc: Panel Self Refresh (PSR/SRD)
+
+.. kernel-doc:: drivers/gpu/drm/i915/display/intel_psr.c
+   :internal:
diff --git a/Documentation/gpu/intel-display/snps-phy.rst b/Documentation/gpu/intel-display/snps-phy.rst
new file mode 100644
index 000000000..c9e333fa7
--- /dev/null
+++ b/Documentation/gpu/intel-display/snps-phy.rst
@@ -0,0 +1,8 @@
+.. SPDX-License-Identifier: MIT
+.. Copyright © 2026 Intel Corporation
+
+Synopsis PHY support
+====================
+
+.. kernel-doc:: drivers/gpu/drm/i915/display/intel_snps_phy.c
+   :doc: Synopsis PHY support
diff --git a/Documentation/gpu/intel-display/vbt.rst b/Documentation/gpu/intel-display/vbt.rst
new file mode 100644
index 000000000..be69f7fd7
--- /dev/null
+++ b/Documentation/gpu/intel-display/vbt.rst
@@ -0,0 +1,14 @@
+.. SPDX-License-Identifier: MIT
+.. Copyright © 2026 Intel Corporation
+
+Video BIOS Table (VBT)
+======================
+
+.. kernel-doc:: drivers/gpu/drm/i915/display/intel_bios.c
+   :doc: Video BIOS Table (VBT)
+
+.. kernel-doc:: drivers/gpu/drm/i915/display/intel_bios.c
+   :internal:
+
+.. kernel-doc:: drivers/gpu/drm/i915/display/intel_vbt_defs.h
+   :internal: