diff options
| author | Linus Torvalds <torvalds@linux-foundation.org> | 2026-08-19 10:09:22 -0700 |
|---|---|---|
| committer | Linus Torvalds <torvalds@linux-foundation.org> | 2026-08-19 10:09:22 -0700 |
| commit | f4cdf7ca9a1fdcca413157df19753f388a5a224e (patch) | |
| tree | 60a31895b2446cd7fa27514e8c2843534a0de0da /Documentation/userspace-api/accelerators | |
| download | linux-stable-f4cdf7ca9a1fdcca413157df19753f388a5a224e.tar.gz linux-stable-f4cdf7ca9a1fdcca413157df19753f388a5a224e.zip | |
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
...
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. |
