diff options
Diffstat (limited to 'Documentation/powerpc/cxl.txt')
| -rw-r--r-- | Documentation/powerpc/cxl.txt | 449 |
1 files changed, 0 insertions, 449 deletions
diff --git a/Documentation/powerpc/cxl.txt b/Documentation/powerpc/cxl.txt deleted file mode 100644 index c5e8d5098ed3..000000000000 --- a/Documentation/powerpc/cxl.txt +++ /dev/null @@ -1,449 +0,0 @@ -Coherent Accelerator Interface (CXL) -==================================== - -Introduction -============ - - The coherent accelerator interface is designed to allow the - coherent connection of accelerators (FPGAs and other devices) to a - POWER system. These devices need to adhere to the Coherent - Accelerator Interface Architecture (CAIA). - - IBM refers to this as the Coherent Accelerator Processor Interface - or CAPI. In the kernel it's referred to by the name CXL to avoid - confusion with the ISDN CAPI subsystem. - - Coherent in this context means that the accelerator and CPUs can - both access system memory directly and with the same effective - addresses. - - -Hardware overview -================= - - POWER8/9 FPGA - +----------+ +---------+ - | | | | - | CPU | | AFU | - | | | | - | | | | - | | | | - +----------+ +---------+ - | PHB | | | - | +------+ | PSL | - | | CAPP |<------>| | - +---+------+ PCIE +---------+ - - The POWER8/9 chip has a Coherently Attached Processor Proxy (CAPP) - unit which is part of the PCIe Host Bridge (PHB). This is managed - by Linux by calls into OPAL. Linux doesn't directly program the - CAPP. - - The FPGA (or coherently attached device) consists of two parts. - The POWER Service Layer (PSL) and the Accelerator Function Unit - (AFU). The AFU is used to implement specific functionality behind - the PSL. The PSL, among other things, provides memory address - translation services to allow each AFU direct access to userspace - memory. - - The AFU is the core part of the accelerator (eg. the compression, - crypto etc function). The kernel has no knowledge of the function - of the AFU. Only userspace interacts directly with the AFU. - - The PSL provides the translation and interrupt services that the - AFU needs. This is what the kernel interacts with. For example, if - the AFU needs to read a particular effective address, it sends - that address to the PSL, the PSL then translates it, fetches the - data from memory and returns it to the AFU. If the PSL has a - translation miss, it interrupts the kernel and the kernel services - the fault. The context to which this fault is serviced is based on - who owns that acceleration function. - - POWER8 <-----> PSL Version 8 is compliant to the CAIA Version 1.0. - POWER9 <-----> PSL Version 9 is compliant to the CAIA Version 2.0. - This PSL Version 9 provides new features such as: - * Interaction with the nest MMU on the P9 chip. - * Native DMA support. - * Supports sending ASB_Notify messages for host thread wakeup. - * Supports Atomic operations. - * .... - - Cards with a PSL9 won't work on a POWER8 system and cards with a - PSL8 won't work on a POWER9 system. - -AFU Modes -========= - - There are two programming modes supported by the AFU. Dedicated - and AFU directed. AFU may support one or both modes. - - When using dedicated mode only one MMU context is supported. In - this mode, only one userspace process can use the accelerator at - time. - - When using AFU directed mode, up to 16K simultaneous contexts can - be supported. This means up to 16K simultaneous userspace - applications may use the accelerator (although specific AFUs may - support fewer). In this mode, the AFU sends a 16 bit context ID - with each of its requests. This tells the PSL which context is - associated with each operation. If the PSL can't translate an - operation, the ID can also be accessed by the kernel so it can - determine the userspace context associated with an operation. - - -MMIO space -========== - - A portion of the accelerator MMIO space can be directly mapped - from the AFU to userspace. Either the whole space can be mapped or - just a per context portion. The hardware is self describing, hence - the kernel can determine the offset and size of the per context - portion. - - -Interrupts -========== - - AFUs may generate interrupts that are destined for userspace. These - are received by the kernel as hardware interrupts and passed onto - userspace by a read syscall documented below. - - Data storage faults and error interrupts are handled by the kernel - driver. - - -Work Element Descriptor (WED) -============================= - - The WED is a 64-bit parameter passed to the AFU when a context is - started. Its format is up to the AFU hence the kernel has no - knowledge of what it represents. Typically it will be the - effective address of a work queue or status block where the AFU - and userspace can share control and status information. - - - - -User API -======== - -1. AFU character devices - - For AFUs operating in AFU directed mode, two character device - files will be created. /dev/cxl/afu0.0m will correspond to a - master context and /dev/cxl/afu0.0s will correspond to a slave - context. Master contexts have access to the full MMIO space an - AFU provides. Slave contexts have access to only the per process - MMIO space an AFU provides. - - For AFUs operating in dedicated process mode, the driver will - only create a single character device per AFU called - /dev/cxl/afu0.0d. This will have access to the entire MMIO space - that the AFU provides (like master contexts in AFU directed). - - The types described below are defined in include/uapi/misc/cxl.h - - The following file operations are supported on both slave and - master devices. - - A userspace library libcxl is available here: - https://github.com/ibm-capi/libcxl - This provides a C interface to this kernel API. - -open ----- - - Opens the device and allocates a file descriptor to be used with - the rest of the API. - - A dedicated mode AFU only has one context and only allows the - device to be opened once. - - An AFU directed mode AFU can have many contexts, the device can be - opened once for each context that is available. - - When all available contexts are allocated the open call will fail - and return -ENOSPC. - - Note: IRQs need to be allocated for each context, which may limit - the number of contexts that can be created, and therefore - how many times the device can be opened. The POWER8 CAPP - supports 2040 IRQs and 3 are used by the kernel, so 2037 are - left. If 1 IRQ is needed per context, then only 2037 - contexts can be allocated. If 4 IRQs are needed per context, - then only 2037/4 = 509 contexts can be allocated. - - -ioctl ------ - - CXL_IOCTL_START_WORK: - Starts the AFU context and associates it with the current - process. Once this ioctl is successfully executed, all memory - mapped into this process is accessible to this AFU context - using the same effective addresses. No additional calls are - required to map/unmap memory. The AFU memory context will be - updated as userspace allocates and frees memory. This ioctl - returns once the AFU context is started. - - Takes a pointer to a struct cxl_ioctl_start_work: - - struct cxl_ioctl_start_work { - __u64 flags; - __u64 work_element_descriptor; - __u64 amr; - __s16 num_interrupts; - __s16 reserved1; - __s32 reserved2; - __u64 reserved3; - __u64 reserved4; - __u64 reserved5; - __u64 reserved6; - }; - - flags: - Indicates which optional fields in the structure are - valid. - - work_element_descriptor: - The Work Element Descriptor (WED) is a 64-bit argument - defined by the AFU. Typically this is an effective - address pointing to an AFU specific structure - describing what work to perform. - - amr: - Authority Mask Register (AMR), same as the powerpc - AMR. This field is only used by the kernel when the - corresponding CXL_START_WORK_AMR value is specified in - flags. If not specified the kernel will use a default - value of 0. - - num_interrupts: - Number of userspace interrupts to request. This field - is only used by the kernel when the corresponding - CXL_START_WORK_NUM_IRQS value is specified in flags. - If not specified the minimum number required by the - AFU will be allocated. The min and max number can be - obtained from sysfs. - - reserved fields: - For ABI padding and future extensions - - CXL_IOCTL_GET_PROCESS_ELEMENT: - Get the current context id, also known as the process element. - The value is returned from the kernel as a __u32. - - -mmap ----- - - An AFU may have an MMIO space to facilitate communication with the - AFU. If it does, the MMIO space can be accessed via mmap. The size - and contents of this area are specific to the particular AFU. The - size can be discovered via sysfs. - - In AFU directed mode, master contexts are allowed to map all of - the MMIO space and slave contexts are allowed to only map the per - process MMIO space associated with the context. In dedicated - process mode the entire MMIO space can always be mapped. - - This mmap call must be done after the START_WORK ioctl. - - Care should be taken when accessing MMIO space. Only 32 and 64-bit - accesses are supported by POWER8. Also, the AFU will be designed - with a specific endianness, so all MMIO accesses should consider - endianness (recommend endian(3) variants like: le64toh(), - be64toh() etc). These endian issues equally apply to shared memory - queues the WED may describe. - - -read ----- - - Reads events from the AFU. Blocks if no events are pending - (unless O_NONBLOCK is supplied). Returns -EIO in the case of an - unrecoverable error or if the card is removed. - - read() will always return an integral number of events. - - The buffer passed to read() must be at least 4K bytes. - - The result of the read will be a buffer of one or more events, - each event is of type struct cxl_event, of varying size. - - struct cxl_event { - struct cxl_event_header header; - union { - struct cxl_event_afu_interrupt irq; - struct cxl_event_data_storage fault; - struct cxl_event_afu_error afu_error; - }; - }; - - The struct cxl_event_header is defined as: - - struct cxl_event_header { - __u16 type; - __u16 size; - __u16 process_element; - __u16 reserved1; - }; - - type: - This defines the type of event. The type determines how - the rest of the event is structured. These types are - described below and defined by enum cxl_event_type. - - size: - This is the size of the event in bytes including the - struct cxl_event_header. The start of the next event can - be found at this offset from the start of the current - event. - - process_element: - Context ID of the event. - - reserved field: - For future extensions and padding. - - If the event type is CXL_EVENT_AFU_INTERRUPT then the event - structure is defined as: - - struct cxl_event_afu_interrupt { - __u16 flags; - __u16 irq; /* Raised AFU interrupt number */ - __u32 reserved1; - }; - - flags: - These flags indicate which optional fields are present - in this struct. Currently all fields are mandatory. - - irq: - The IRQ number sent by the AFU. - - reserved field: - For future extensions and padding. - - If the event type is CXL_EVENT_DATA_STORAGE then the event - structure is defined as: - - struct cxl_event_data_storage { - __u16 flags; - __u16 reserved1; - __u32 reserved2; - __u64 addr; - __u64 dsisr; - __u64 reserved3; - }; - - flags: - These flags indicate which optional fields are present in - this struct. Currently all fields are mandatory. - - address: - The address that the AFU unsuccessfully attempted to - access. Valid accesses will be handled transparently by the - kernel but invalid accesses will generate this event. - - dsisr: - This field gives information on the type of fault. It is a - copy of the DSISR from the PSL hardware when the address - fault occurred. The form of the DSISR is as defined in the - CAIA. - - reserved fields: - For future extensions - - If the event type is CXL_EVENT_AFU_ERROR then the event structure - is defined as: - - struct cxl_event_afu_error { - __u16 flags; - __u16 reserved1; - __u32 reserved2; - __u64 error; - }; - - flags: - These flags indicate which optional fields are present in - this struct. Currently all fields are Mandatory. - - error: - Error status from the AFU. Defined by the AFU. - - reserved fields: - For future extensions and padding - - -2. Card character device (powerVM guest only) - - In a powerVM guest, an extra character device is created for the - card. The device is only used to write (flash) a new image on the - FPGA accelerator. Once the image is written and verified, the - device tree is updated and the card is reset to reload the updated - image. - -open ----- - - Opens the device and allocates a file descriptor to be used with - the rest of the API. The device can only be opened once. - -ioctl ------ - -CXL_IOCTL_DOWNLOAD_IMAGE: -CXL_IOCTL_VALIDATE_IMAGE: - Starts and controls flashing a new FPGA image. Partial - reconfiguration is not supported (yet), so the image must contain - a copy of the PSL and AFU(s). Since an image can be quite large, - the caller may have to iterate, splitting the image in smaller - chunks. - - Takes a pointer to a struct cxl_adapter_image: - struct cxl_adapter_image { - __u64 flags; - __u64 data; - __u64 len_data; - __u64 len_image; - __u64 reserved1; - __u64 reserved2; - __u64 reserved3; - __u64 reserved4; - }; - - flags: - These flags indicate which optional fields are present in - this struct. Currently all fields are mandatory. - - data: - Pointer to a buffer with part of the image to write to the - card. - - len_data: - Size of the buffer pointed to by data. - - len_image: - Full size of the image. - - -Sysfs Class -=========== - - A cxl sysfs class is added under /sys/class/cxl to facilitate - enumeration and tuning of the accelerators. Its layout is - described in Documentation/ABI/testing/sysfs-class-cxl - - -Udev rules -========== - - The following udev rules could be used to create a symlink to the - most logical chardev to use in any programming mode (afuX.Yd for - dedicated, afuX.Ys for afu directed), since the API is virtually - identical for each: - - SUBSYSTEM=="cxl", ATTRS{mode}=="dedicated_process", SYMLINK="cxl/%b" - SUBSYSTEM=="cxl", ATTRS{mode}=="afu_directed", \ - KERNEL=="afu[0-9]*.[0-9]*s", SYMLINK="cxl/%b" |