Merge tag 'media/v7.3-1' of git://git.kernel.org/pub/scm/linux/kernel/git/mchehab/linux-mediagrafted

Pull media updates from Mauro Carvalho Chehab:

 - v4l2-core: added ISP statistics support and per-block validation

 - v4l2-core: Allow unknown HDR10 white point and luminance

 - New camera sensors: Sony IMX678 and IMX471m, Himax HM1092 IR sensor

 - New codec: Milos: VPU v2.0 codec support

 - isp driver: gained support for Dreamchip RPPX1 ISP framework

 - vsp1 driver: gained support for RZ/T2H and RZ/N2H

 - Novalake driver: gained CVS support for new NVL hardware

 - dvb-core: fix feed leak on failed DMX_ADD_PID

 - several driver fixes, cleanups and minor improvements

* tag 'media/v7.3-1' of git://git.kernel.org/pub/scm/linux/kernel/git/mchehab/linux-media: (308 commits)
  media: ipu-bridge: check all DMI entries when overriding sensor rotation
  media: v4l2-async: avoid deleting unlinked ASC entry on link error
  media: rzg2l-cru: Align bytesperline to hardware DMA stride requirement
  media: intel/ipu6: fix async notifier cleanup leak on parse error
  media: staging/ipu7: fix async notifier UAF on probe error path
  media: amd: isp4: fix self-deadlock in isp4sd_pwron_and_init() error path
  media: amd: isp4: release partial allocations in isp4if_alloc_fw_gpumem()
  media: rcar-isp: Fix VSPX reference leaks
  media: rcar-isp: Release ISPCORE resources
  media: i2c: imx415: Release runtime PM reference on VBLANK error
  media: i2c: imx415: Return test pattern write errors
  media: renesas: vsp1: Declare index variables in for loop statement
  media: renesas: vsp1: Make reset control optional to support platforms without a reset line
  media: dt-bindings: media: renesas,vsp1: Document RZ/T2H and RZ/N2H SoCs
  media: dt-bindings: media: renesas,fcp: Document RZ/T2H and RZ/N2H SoCs
  media: nxp: imx8-isi: Add additional 32-bit RGB format support
  media: nxp: imx8-isi: Add 16-bit raw Bayer format support
  media: nxp: imx8-isi: Implement per-stream reference counting for multiplexed streams
  media: nxp: imx8-isi: Use BIT_ULL() for 64-bit stream masks
  media: nxp: imx8-isi: Correct color map between V4L2 and ISI
  ...

1 files changed, 232 insertions, 0 deletions

diff --git a/Documentation/userspace-api/rseq.rst b/Documentation/userspace-api/rseq.rst
new file mode 100644
index 000000000..8549a6c61
--- /dev/null
+++ b/Documentation/userspace-api/rseq.rst
@@ -0,0 +1,232 @@
+=====================
+Restartable Sequences
+=====================
+
+Restartable Sequences allow to register a per thread userspace memory area
+to be used as an ABI between kernel and userspace for three purposes:
+
+ * userspace restartable sequences
+
+ * quick access to read the current CPU number, node ID from userspace
+
+ * scheduler time slice extensions
+
+Restartable sequences (per-cpu atomics)
+---------------------------------------
+
+Restartable sequences allow userspace to perform update operations on
+per-cpu data without requiring heavyweight atomic operations. The actual
+ABI is unfortunately only available in the code and selftests.
+
+Quick access to CPU number, node ID
+-----------------------------------
+
+Allows to implement per CPU data efficiently. Documentation is in code and
+selftests. :(
+
+Optimized RSEQ V2
+-----------------
+
+On architectures which utilize the generic entry code and generic TIF bits
+the kernel supports runtime optimizations for RSEQ, which also enable
+enhanced features like scheduler time slice extensions.
+
+To enable them a task has to register the RSEQ region with at least the
+length advertised by getauxval(AT_RSEQ_FEATURE_SIZE).
+
+If existing binaries register with RSEQ_ORIG_SIZE (32 bytes), the kernel
+keeps the legacy low performance mode enabled to fulfil the expectations
+of existing users regarding the original RSEQ implementation behaviour.
+
+The following table documents the ABI and behavioral guarantees of the
+legacy and the optimized V2 mode.
+
+.. list-table:: RSEQ modes
+   :header-rows: 1
+
+   * - Nr
+     - What
+
+     - Legacy
+     - Optimized V2
+
+   * - 1
+     - The cpu_id_start, cpu_id, node_id and mm_cid fields (User mode read
+       only)
+       .. Legacy
+     - Updated by the kernel unconditionally after each context switch and
+       before signal delivery
+       .. Optimized V2
+     - Updated by the kernel if and only if they change, i.e. if the task
+       is migrated or mm_cid changes
+
+   * - 2
+     - The rseq_cs critical section field
+       .. Legacy
+     - Evaluated and handled unconditionally after each context switch and
+       before signal delivery
+       .. Optimized V2
+     - Evaluated and handled conditionally only when user space was
+       interrupted and was scheduled out or before delivering a signal in
+       the interrupted context.
+
+   * - 3
+     - Read only fields
+       .. Legacy
+     - No strict enforcement except in debug mode
+       .. Optimized V2
+     - Strict enforcement
+
+   * - 4
+     - membarrier(...RSEQ)
+       .. Legacy
+     - All running threads of the process are interrupted and the ID fields
+       are rewritten and eventually active critical sections are aborted
+       before they return to user space.  All threads which are scheduled
+       out whether voluntary or not are covered by #1/#2 above.
+       .. Optimized V2
+     - All running threads of the process are interrupted and eventually
+       active critical sections are aborted before these threads return to
+       user space. The ID fields are only updated if changed as a
+       consequence of the interrupt. All threads which are scheduled out
+       whether voluntary or not are covered by #1/#2 above.
+
+   * - 5
+     - Time slice extensions
+       .. Legacy
+     - Not supported
+       .. Optimized V2
+     - Supported
+
+The legacy mode is obviously less performant as it does unconditional
+updates and critical section checks even if not strictly required by the
+ABI contract. That can't be changed anymore as some users depend on that
+observed behavior, which in turn enables them to violate the ABI and
+overwrite the cpu_id_start field for their own purposes. This is obviously
+discouraged as it renders RSEQ incompatible with the intended usage and
+breaks the expectation of other libraries in the same application.
+
+The ABI compliant optimized v2 mode, which respects the read only fields,
+does not require unconditional updates and therefore is way more
+performant. The kernel validates the read only fields for compliance. If
+user space modifies them, the process is killed. Compliant usage allows
+multiple libraries in the same application to benefit from the RSEQ
+functionality without disturbing each other. The ABI compliant optimized v2
+mode also enables extended RSEQ features like time slice extensions.
+
+
+Scheduler time slice extensions
+-------------------------------
+
+This allows a thread to request a time slice extension when it enters a
+critical section to avoid contention on a resource when the thread is
+scheduled out inside of the critical section.
+
+The prerequisites for this functionality are:
+
+    * Enabled in Kconfig
+
+    * Enabled at boot time (default is enabled)
+
+    * A rseq userspace pointer has been registered for the thread in
+      optimized V2 mode
+
+The thread has to enable the functionality via prctl(2)::
+
+    prctl(PR_RSEQ_SLICE_EXTENSION, PR_RSEQ_SLICE_EXTENSION_SET,
+          PR_RSEQ_SLICE_EXT_ENABLE, 0, 0);
+
+prctl() returns 0 on success or otherwise with the following error codes:
+
+========= ==============================================================
+Errorcode Meaning
+========= ==============================================================
+EINVAL	  Functionality not available or invalid function arguments.
+          Note: arg4 and arg5 must be zero
+ENOTSUPP  Functionality was disabled on the kernel command line
+ENXIO	  Available, but no rseq user struct registered
+========= ==============================================================
+
+The state can be also queried via prctl(2)::
+
+  prctl(PR_RSEQ_SLICE_EXTENSION, PR_RSEQ_SLICE_EXTENSION_GET, 0, 0, 0);
+
+prctl() returns ``PR_RSEQ_SLICE_EXT_ENABLE`` when it is enabled or 0 if
+disabled. Otherwise it returns with the following error codes:
+
+========= ==============================================================
+Errorcode Meaning
+========= ==============================================================
+EINVAL	  Functionality not available or invalid function arguments.
+          Note: arg3 and arg4 and arg5 must be zero
+========= ==============================================================
+
+The availability and status is also exposed via the rseq ABI struct flags
+field via the ``RSEQ_CS_FLAG_SLICE_EXT_AVAILABLE_BIT`` and the
+``RSEQ_CS_FLAG_SLICE_EXT_ENABLED_BIT``. These bits are read-only for user
+space and only for informational purposes.
+
+If the mechanism was enabled via prctl(), the thread can request a time
+slice extension by setting rseq::slice_ctrl::request to 1. If the thread is
+interrupted and the interrupt results in a reschedule request in the
+kernel, then the kernel can grant a time slice extension and return to
+userspace instead of scheduling out. The length of the extension is
+determined by debugfs:rseq/slice_ext_nsec. The default value is 5 usec; which
+is the minimum value. It can be incremented to 50 usecs, however doing so
+can/will affect the minimum scheduling latency.
+
+Any proposed changes to this default will have to come with a selftest and
+rseq-slice-hist.py output that shows the new value has merrit.
+
+The kernel indicates the grant by clearing rseq::slice_ctrl::request and
+setting rseq::slice_ctrl::granted to 1. If there is a reschedule of the
+thread after granting the extension, the kernel clears the granted bit to
+indicate that to userspace.
+
+If the request bit is still set when the leaving the critical section,
+userspace can clear it and continue.
+
+If the granted bit is set, then userspace invokes rseq_slice_yield(2) when
+leaving the critical section to relinquish the CPU. The kernel enforces
+this by arming a timer to prevent misbehaving userspace from abusing this
+mechanism.
+
+If both the request bit and the granted bit are false when leaving the
+critical section, then this indicates that a grant was revoked and no
+further action is required by userspace.
+
+The required code flow is as follows::
+
+    rseq->slice_ctrl.request = 1;
+    barrier();  // Prevent compiler reordering
+    critical_section();
+    barrier();  // Prevent compiler reordering
+    rseq->slice_ctrl.request = 0;
+    if (rseq->slice_ctrl.granted)
+        rseq_slice_yield();
+
+As all of this is strictly CPU local, there are no atomicity requirements.
+Checking the granted state is racy, but that cannot be avoided at all::
+
+    if (rseq->slice_ctrl.granted)
+      -> Interrupt results in schedule and grant revocation
+        rseq_slice_yield();
+
+So there is no point in pretending that this might be solved by an atomic
+operation.
+
+If the thread issues a syscall other than rseq_slice_yield(2) within the
+granted timeslice extension, the grant is also revoked and the CPU is
+relinquished immediately when entering the kernel. This is required as
+syscalls might consume arbitrary CPU time until they reach a scheduling
+point when the preemption model is either NONE or VOLUNTARY and therefore
+might exceed the grant by far.
+
+The preferred solution for user space is to use rseq_slice_yield(2) which
+is side effect free. The support for arbitrary syscalls is required to
+support onion layer architectured applications, where the code handling the
+critical section and requesting the time slice extension has no control
+over the code within the critical section.
+
+The kernel enforces flag consistency and terminates the thread with SIGSEGV
+if it detects a violation.