This patch set is intended for the 4.3 release and adds support for the superpipe features provided by the IBM CXL Flash adapter. This function was originally presented in an RFC patch set in late April. To ease the digestion of these enhancements, we have further split it across the two patches in this set.
The IBM Power processor architecture provides support for CAPI (Coherent Accelerator Power Interface), which is available to certain PCIe slots on Power 8 systems. CAPI can be thought of as a special tunneling protocol through PCIe that allow PCIe adapters to look like special purpose co-processors which can read or write an application's memory and generate page faults. As a result, the host interface to an adapter running in CAPI mode does not require data buffers to be mapped to the device's memory (IOMMU bypass) nor does it require memory to be pinned. Application specific accelerators are constructed by burning logic to either an FPGA or ASIC that accelerates a certain function in hardware. This logic is referred to as an Accelerator Function Unit or AFU. AFUs and their associated software are designed to leverage the benefits that CAPI provides to reduce the burden on CPUs and achieve higher performance. Examples of AFUs include compression, encryption, sorting, etc. The cxlflash adapter contains an AFU that enhances the performance of accessing an external flash storage device by allowing user space applications to establish a 'superpipe' through which they may directly access the storage, bypassing the traditional storage stack and reducing path length per-I/O by more than an order of magnitude. The AFU also supports a translation function that allows users to segment a physical device into 'n' virtual devices [by programmatic means] and refer to these segments as if they were a true physical device. This function enables a more efficient use of a physical device and provides for a secure multi-tenant environment. At a high-level, the cxlflash adapter looks and behaves very much like a SCSI HBA. Like other SCSI adapters it understands SCSI CDBs and LUN discovery. It also provides health monitoring, error recovery, and link event reporting. At a lower level, the cxlflash adapter requires some additional items not found in a traditional SCSI HBA driver. These include the following: - A programmatic API (implemented as ioctls) that user applications interact with when they desire to take advantage of the superpipe access from user space. These ioctls allow the user to gain access to the CAPI resources (ie: interrupts, MMIO space, etc.) that are required to use the superpipe. Additionally, they allow applications to use the AFUs virtual partitioning function. Note that while the ioctls are new, under the covers they make use of existing functionality found in the cxl driver (drivers/misc/cxl). - A block allocation table (implemented as a bitmap) per physical device attached to the cxlflash adapter that is operating in the virtual partitioned mode. This table manages the segmentation of the physical device and is used to derive the entries found in the LUN mapping table. - A LUN mapping table that is shared with the AFU and used by the AFU to associate the resource handles referring to a specific virtual device with blocks on the physical device. - The ability to send a limited set of SCSI commands directly to the adapter to determine capacity and identification data as well as wipe blocks that are no longer in use when a virtual device is released. This set of commands includes READ_CAPACITY and WRITE_SAME. Accompanying this adapter driver but not included here is a user space library (known as the block library) that will hide the interaction between user space and the cxlflash driver. Most (if not all) users will chose to use this library when developing superpipe-aware applications. The block library can be found on Github: https://github.com/mikehollinger/ibmcapikv More technical details are found within Documentation/powerpc/cxlflash.txt The following patches are bisectable: Patch 1 contains base enablement of superpipe function. Patch 2 adds support for segmentation of physical LUNs from user space. Matthew R. Ochs (2): cxlflash: Base superpipe support cxlflash: Virtual LUN support Documentation/powerpc/cxlflash.txt | 298 ++++++ drivers/scsi/cxlflash/Makefile | 2 +- drivers/scsi/cxlflash/common.h | 18 + drivers/scsi/cxlflash/main.c | 12 + drivers/scsi/cxlflash/superpipe.c | 1884 ++++++++++++++++++++++++++++++++++++ drivers/scsi/cxlflash/superpipe.h | 210 ++++ drivers/scsi/cxlflash/vlun.c | 1096 +++++++++++++++++++++ include/uapi/scsi/cxlflash_ioctl.h | 159 +++ 8 files changed, 3678 insertions(+), 1 deletion(-) create mode 100644 Documentation/powerpc/cxlflash.txt create mode 100644 drivers/scsi/cxlflash/superpipe.c create mode 100644 drivers/scsi/cxlflash/superpipe.h create mode 100644 drivers/scsi/cxlflash/vlun.c create mode 100644 include/uapi/scsi/cxlflash_ioctl.h -- 2.1.0 -- To unsubscribe from this list: send the line "unsubscribe linux-scsi" in
