[PATCH v4 16/16] cxl: Add documentation for userspace APIs
Michael Neuling
mikey at neuling.org
Wed Oct 8 19:55:05 EST 2014
From: Ian Munsie <imunsie at au1.ibm.com>
This documentation gives an overview of the hardware architecture, userspace
APIs via /dev/cxl/afuM.N and the syfs files. It also adds a MAINTAINERS file
entry for cxl.
Signed-off-by: Ian Munsie <imunsie at au1.ibm.com>
Signed-off-by: Michael Neuling <mikey at neuling.org>
---
Documentation/ABI/testing/sysfs-class-cxl | 130 ++++++++++
Documentation/ioctl/ioctl-number.txt | 1 +
Documentation/powerpc/00-INDEX | 2 +
Documentation/powerpc/cxl.txt | 379 ++++++++++++++++++++++++++++++
MAINTAINERS | 12 +
include/uapi/misc/cxl.h | 7 +-
6 files changed, 528 insertions(+), 3 deletions(-)
create mode 100644 Documentation/ABI/testing/sysfs-class-cxl
create mode 100644 Documentation/powerpc/cxl.txt
diff --git a/Documentation/ABI/testing/sysfs-class-cxl b/Documentation/ABI/testing/sysfs-class-cxl
new file mode 100644
index 0000000..0a5508c
--- /dev/null
+++ b/Documentation/ABI/testing/sysfs-class-cxl
@@ -0,0 +1,130 @@
+Slave contexts (eg. /sys/class/cxl/afu0.0s):
+
+What: /sys/class/cxl/<afu>/irqs_max
+Date: September 2014
+Contact: linuxppc-dev at lists.ozlabs.org
+Description: read/write
+ Decimal value of maximum number of interrupts that can be
+ requested by userspace. The default on probe is the maximum
+ that hardware can support (eg. 2037). Write values will limit
+ userspace applications to that many userspace interrupts. Must
+ be >= irqs_min.
+
+What: /sys/class/cxl/<afu>/irqs_min
+Date: September 2014
+Contact: linuxppc-dev at lists.ozlabs.org
+Description: read only
+ Decimal value of the minimum number of interrupts that
+ userspace must request on a CXL_START_WORK ioctl. Userspace may
+ omit the num_interrupts field in the START_WORK IOCTL to get
+ this minimum automatically.
+
+What: /sys/class/cxl/<afu>/mmio_size
+Date: September 2014
+Contact: linuxppc-dev at lists.ozlabs.org
+Description: read only
+ Decimal value of the size of the MMIO space that may be mmaped
+ by userspace.
+
+What: /sys/class/cxl/<afu>/modes_supported
+Date: September 2014
+Contact: linuxppc-dev at lists.ozlabs.org
+Description: read only
+ List of the modes this AFU supports. One per line.
+ Valid entries are: "dedicated_process" and "afu_directed"
+
+What: /sys/class/cxl/<afu>/mode
+Date: September 2014
+Contact: linuxppc-dev at lists.ozlabs.org
+Description: read/write
+ The current mode the AFU is using. Will be one of the modes
+ given in modes_supported. Writing will change the mode
+ provided that no user contexts are attached.
+
+
+What: /sys/class/cxl/<afu>/prefault_mode
+Date: September 2014
+Contact: linuxppc-dev at lists.ozlabs.org
+Description: read/write
+ Set the mode for prefaulting in segments into the segment table
+ when performing the START_WORK ioctl. Possible values:
+ none: No prefaulting (default)
+ work_element_descriptor: Treat the work element
+ descriptor as an effective address and
+ prefault what it points to.
+ all: all segments process calling START_WORK maps.
+
+What: /sys/class/cxl/<afu>/reset
+Date: September 2014
+Contact: linuxppc-dev at lists.ozlabs.org
+Description: write only
+ Writing 1 here will reset the AFU provided there are not
+ contexts active on the AFU.
+
+What: /sys/class/cxl/<afu>/api_version
+Date: September 2014
+Contact: linuxppc-dev at lists.ozlabs.org
+Description: read only
+ Decimal value of the current version of the kernel/user API.
+
+What: /sys/class/cxl/<afu>/api_version_com
+Date: September 2014
+Contact: linuxppc-dev at lists.ozlabs.org
+Description: read only
+ Decimal value of the the lowest version of the userspace API
+ this this kernel supports.
+
+
+
+Master contexts (eg. /sys/class/cxl/afu0.0m)
+
+What: /sys/class/cxl/<afu>m/mmio_size
+Date: September 2014
+Contact: linuxppc-dev at lists.ozlabs.org
+Description: read only
+ Decimal value of the size of the MMIO space that may be mmaped
+ by userspace. This includes all slave contexts space also.
+
+What: /sys/class/cxl/<afu>m/pp_mmio_len
+Date: September 2014
+Contact: linuxppc-dev at lists.ozlabs.org
+Description: read only
+ Decimal value of the Per Process MMIO space length.
+
+What: /sys/class/cxl/<afu>m/pp_mmio_off
+Date: September 2014
+Contact: linuxppc-dev at lists.ozlabs.org
+Description: read only
+ Decimal value of the Per Process MMIO space offset.
+
+
+Card info (eg. /sys/class/cxl/card0)
+
+What: /sys/class/cxl/<card>/caia_version
+Date: September 2014
+Contact: linuxppc-dev at lists.ozlabs.org
+Description: read only
+ Identifies the CAIA Version the card implements.
+
+What: /sys/class/cxl/<card>/psl_version
+Date: September 2014
+Contact: linuxppc-dev at lists.ozlabs.org
+Description: read only
+ Identifies the revision level of the PSL.
+
+What: /sys/class/cxl/<card>/base_image
+Date: September 2014
+Contact: linuxppc-dev at lists.ozlabs.org
+Description: read only
+ Identifies the revision level of the base image for devices
+ that support loadable PSLs. For FPGAs this field identifies
+ the image contained in the on-adapter flash which is loaded
+ during the initial program load.
+
+What: /sys/class/cxl/<card>/image_loaded
+Date: September 2014
+Contact: linuxppc-dev at lists.ozlabs.org
+Description: read only
+ Will return "user" or "factory" depending on the image loaded
+ onto the card.
+
diff --git a/Documentation/ioctl/ioctl-number.txt b/Documentation/ioctl/ioctl-number.txt
index 7e240a7..8136e1f 100644
--- a/Documentation/ioctl/ioctl-number.txt
+++ b/Documentation/ioctl/ioctl-number.txt
@@ -313,6 +313,7 @@ Code Seq#(hex) Include File Comments
0xB1 00-1F PPPoX <mailto:mostrows at styx.uwaterloo.ca>
0xB3 00 linux/mmc/ioctl.h
0xC0 00-0F linux/usb/iowarrior.h
+0xCA 00-0F uapi/misc/cxl.h
0xCB 00-1F CBM serial IEC bus in development:
<mailto:michael.klein at puffin.lb.shuttle.de>
0xCD 01 linux/reiserfs_fs.h
diff --git a/Documentation/powerpc/00-INDEX b/Documentation/powerpc/00-INDEX
index a68784d..6fd0e8b 100644
--- a/Documentation/powerpc/00-INDEX
+++ b/Documentation/powerpc/00-INDEX
@@ -11,6 +11,8 @@ bootwrapper.txt
cpu_features.txt
- info on how we support a variety of CPUs with minimal compile-time
options.
+cxl.txt
+ - Overview of the CXL driver.
eeh-pci-error-recovery.txt
- info on PCI Bus EEH Error Recovery
firmware-assisted-dump.txt
diff --git a/Documentation/powerpc/cxl.txt b/Documentation/powerpc/cxl.txt
new file mode 100644
index 0000000..2c71ecc
--- /dev/null
+++ b/Documentation/powerpc/cxl.txt
@@ -0,0 +1,379 @@
+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 FPGA
+ +----------+ +---------+
+ | | | |
+ | CPU | | AFU |
+ | | | |
+ | | | |
+ | | | |
+ +----------+ +---------+
+ | PHB | | |
+ | +------+ | PSL |
+ | | CAPP |<------>| |
+ +---+------+ PCIE +---------+
+
+ The POWER8 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.
+
+
+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
+========
+
+ 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.
+
+
+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
+
+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"
diff --git a/MAINTAINERS b/MAINTAINERS
index 809ecd6..facc219 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -2711,6 +2711,18 @@ W: http://www.chelsio.com
S: Supported
F: drivers/net/ethernet/chelsio/cxgb4vf/
+CXL (IBM Coherent Accelerator Processor Interface CAPI) DRIVER
+M: Ian Munsie <imunsie at au1.ibm.com>
+M: Michael Neuling <mikey at neuling.org>
+L: linuxppc-dev at lists.ozlabs.org
+S: Supported
+F: drivers/misc/cxl/
+F: include/misc/cxl.h
+F: include/uapi/misc/cxl.h
+F: Documentation/powerpc/cxl.txt
+F: Documentation/powerpc/cxl.txt
+F: Documentation/ABI/testing/sysfs-class-cxl
+
STMMAC ETHERNET DRIVER
M: Giuseppe Cavallaro <peppe.cavallaro at st.com>
L: netdev at vger.kernel.org
diff --git a/include/uapi/misc/cxl.h b/include/uapi/misc/cxl.h
index c232be6..cd6d789 100644
--- a/include/uapi/misc/cxl.h
+++ b/include/uapi/misc/cxl.h
@@ -13,7 +13,7 @@
#include <linux/types.h>
#include <linux/ioctl.h>
-/* Structs for IOCTLS for userspace to talk to the kernel */
+
struct cxl_ioctl_start_work {
__u64 flags;
__u64 work_element_descriptor;
@@ -26,19 +26,20 @@ struct cxl_ioctl_start_work {
__u64 reserved5;
__u64 reserved6;
};
+
#define CXL_START_WORK_AMR 0x0000000000000001ULL
#define CXL_START_WORK_NUM_IRQS 0x0000000000000002ULL
#define CXL_START_WORK_ALL (CXL_START_WORK_AMR |\
CXL_START_WORK_NUM_IRQS)
-/* IOCTL numbers */
+/* ioctl numbers */
#define CXL_MAGIC 0xCA
#define CXL_IOCTL_START_WORK _IOW(CXL_MAGIC, 0x00, struct cxl_ioctl_start_work)
#define CXL_IOCTL_GET_PROCESS_ELEMENT _IOR(CXL_MAGIC, 0x01, __u32)
-/* Events from read() */
#define CXL_READ_MIN_SIZE 0x1000 /* 4K */
+/* Events from read() */
enum cxl_event_type {
CXL_EVENT_RESERVED = 0,
CXL_EVENT_AFU_INTERRUPT = 1,
--
1.9.1
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