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| author | Kees Cook <kees+treewide@kernel.org> | 2026-09-02 15:31:14 -0700 |
|---|---|---|
| committer | Kees Cook <kees@kernel.org> | 2026-09-04 21:37:00 -0700 |
| commit | 3a2c4d55e32ad65efebdb6de44eef3bfa08bb49d (patch) | |
| tree | c65086f9bdcd48c6360fb7cb4598bca084da1f32 /Documentation/userspace-api/accelerators | |
| download | linux-stable-3a2c4d55e32ad65efebdb6de44eef3bfa08bb49d.tar.gz linux-stable-3a2c4d55e32ad65efebdb6de44eef3bfa08bb49d.zip | |
treewide: refresh kmalloc_obj() conversionsgrafted
This is another run of the Coccinelle script for converting kmalloc()
family of allocations to kmalloc_obj() via the existing rules in
scripts/coccinelle/api/kmalloc_objs.cocci
This catches both the set of kmalloc() uses added since the first
kmalloc_obj() conversions in v7.0 and adds a large group missed in the
first pass due to Coccinelle not interacting well with the cleanup.h
scoped_...() family of macros[1]. I worked around this with spatch's
"--macro-file" argument to a file with all the scoped_...() macros mapped
to Coccinelle's YACFE_ITERATOR[2] as that was the closest viable control
flow indicator I could find.
Build tested allmodconfig on x86, arm64, arm, loongarch, mips, powerpc,
riscv, and s390 with no new warnings.
Link: https://lore.kernel.org/lkml/202609021314.8A9C0B8@keescook/ [1]
Link: https://github.com/coccinelle/coccinelle/blob/master/standard.h [2]
Signed-off-by: Kees Cook <kees+treewide@kernel.org>
Diffstat (limited to 'Documentation/userspace-api/accelerators')
| -rw-r--r-- | Documentation/userspace-api/accelerators/ocxl.rst | 179 |
1 files changed, 179 insertions, 0 deletions
diff --git a/Documentation/userspace-api/accelerators/ocxl.rst b/Documentation/userspace-api/accelerators/ocxl.rst new file mode 100644 index 000000000..4e213af70 --- /dev/null +++ b/Documentation/userspace-api/accelerators/ocxl.rst @@ -0,0 +1,179 @@ +======================================================== +OpenCAPI (Open Coherent Accelerator Processor Interface) +======================================================== + +OpenCAPI is an interface between processors and accelerators. It aims +at being low-latency and high-bandwidth. + +The specification was developed by the OpenCAPI Consortium, and is now +available from the `Compute Express Link Consortium +<https://computeexpresslink.org/resource/opencapi-specification-archive/>`_. + +It allows an accelerator (which could be an FPGA, ASICs, ...) to access +the host memory coherently, using virtual addresses. An OpenCAPI +device can also host its own memory, that can be accessed from the +host. + +OpenCAPI is known in linux as 'ocxl', as the open, processor-agnostic +evolution of 'cxl' (the driver for the IBM CAPI interface for +powerpc), which was named that way to avoid confusion with the ISDN +CAPI subsystem. + + +High-level view +=============== + +OpenCAPI defines a Data Link Layer (DL) and Transaction Layer (TL), to +be implemented on top of a physical link. Any processor or device +implementing the DL and TL can start sharing memory. + +:: + + +-----------+ +-------------+ + | | | | + | | | Accelerated | + | Processor | | Function | + | | +--------+ | Unit | +--------+ + | |--| Memory | | (AFU) |--| Memory | + | | +--------+ | | +--------+ + +-----------+ +-------------+ + | | + +-----------+ +-------------+ + | TL | | TLX | + +-----------+ +-------------+ + | | + +-----------+ +-------------+ + | DL | | DLX | + +-----------+ +-------------+ + | | + | PHY | + +---------------------------------------+ + + + +Device discovery +================ + +OpenCAPI relies on a PCI-like configuration space, implemented on the +device. So the host can discover AFUs by querying the config space. + +OpenCAPI devices in Linux are treated like PCI devices (with a few +caveats). The firmware is expected to abstract the hardware as if it +was a PCI link. A lot of the existing PCI infrastructure is reused: +devices are scanned and BARs are assigned during the standard PCI +enumeration. Commands like 'lspci' can therefore be used to see what +devices are available. + +The configuration space defines the AFU(s) that can be found on the +physical adapter, such as its name, how many memory contexts it can +work with, the size of its MMIO areas, ... + + + +MMIO +==== + +OpenCAPI defines two MMIO areas for each AFU: + +* the global MMIO area, with registers pertinent to the whole AFU. +* a per-process MMIO area, which has a fixed size for each context. + + + +AFU interrupts +============== + +OpenCAPI includes the possibility for an AFU to send an interrupt to a +host process. It is done through a 'intrp_req' defined in the +Transaction Layer, specifying a 64-bit object handle which defines the +interrupt. + +The driver allows a process to allocate an interrupt and obtain its +64-bit object handle, that can be passed to the AFU. + + + +char devices +============ + +The driver creates one char device per AFU found on the physical +device. A physical device may have multiple functions and each +function can have multiple AFUs. At the time of this writing though, +it has only been tested with devices exporting only one AFU. + +Char devices can be found in /dev/ocxl/ and are named as: +/dev/ocxl/<AFU name>.<location>.<index> + +where <AFU name> is a max 20-character long name, as found in the +config space of the AFU. +<location> is added by the driver and can help distinguish devices +when a system has more than one instance of the same OpenCAPI device. +<index> is also to help distinguish AFUs in the unlikely case where a +device carries multiple copies of the same AFU. + + + +Sysfs class +=========== + +An ocxl class is added for the devices representing the AFUs. See +/sys/class/ocxl. The layout is described in +Documentation/ABI/testing/sysfs-class-ocxl + + + +User API +======== + +open +---- + +Based on the AFU definition found in the config space, an AFU may +support working with more than one memory context, in which case the +associated char device may be opened multiple times by different +processes. + + +ioctl +----- + +OCXL_IOCTL_ATTACH: + + Attach the memory context of the calling process to the AFU so that + the AFU can access its memory. + +OCXL_IOCTL_IRQ_ALLOC: + + Allocate an AFU interrupt and return an identifier. + +OCXL_IOCTL_IRQ_FREE: + + Free a previously allocated AFU interrupt. + +OCXL_IOCTL_IRQ_SET_FD: + + Associate an event fd to an AFU interrupt so that the user process + can be notified when the AFU sends an interrupt. + +OCXL_IOCTL_GET_METADATA: + + Obtains configuration information from the card, such at the size of + MMIO areas, the AFU version, and the PASID for the current context. + +OCXL_IOCTL_ENABLE_P9_WAIT: + + Allows the AFU to wake a userspace thread executing 'wait'. Returns + information to userspace to allow it to configure the AFU. Note that + this is only available on POWER9. + +OCXL_IOCTL_GET_FEATURES: + + Reports on which CPU features that affect OpenCAPI are usable from + userspace. + + +mmap +---- + +A process can mmap the per-process MMIO area for interactions with the +AFU. |
