1.. SPDX-License-Identifier: GPL-2.0 2 3================================= 4Megaraid Common Management Module 5================================= 6 7Overview 8-------- 9 10Different classes of controllers from LSI Logic accept and respond to the 11user applications in a similar way. They understand the same firmware control 12commands. Furthermore, the applications also can treat different classes of 13the controllers uniformly. Hence it is logical to have a single module that 14interfaces with the applications on one side and all the low level drivers 15on the other. 16 17The advantages, though obvious, are listed for completeness: 18 19 i. Avoid duplicate code from the low level drivers. 20 ii. Unburden the low level drivers from having to export the 21 character node device and related handling. 22 iii. Implement any policy mechanisms in one place. 23 iv. Applications have to interface with only module instead of 24 multiple low level drivers. 25 26Currently this module (called Common Management Module) is used only to issue 27ioctl commands. But this module is envisioned to handle all user space level 28interactions. So any 'proc', 'sysfs' implementations will be localized in this 29common module. 30 31Credits 32------- 33 34:: 35 36 "Shared code in a third module, a "library module", is an acceptable 37 solution. modprobe automatically loads dependent modules, so users 38 running "modprobe driver1" or "modprobe driver2" would automatically 39 load the shared library module." 40 41- Jeff Garzik (jgarzik@pobox.com), 02.25.2004 LKML 42 43:: 44 45 "As Jeff hinted, if your userspace<->driver API is consistent between 46 your new MPT-based RAID controllers and your existing megaraid driver, 47 then perhaps you need a single small helper module (lsiioctl or some 48 better name), loaded by both mptraid and megaraid automatically, which 49 handles registering the /dev/megaraid node dynamically. In this case, 50 both mptraid and megaraid would register with lsiioctl for each 51 adapter discovered, and lsiioctl would essentially be a switch, 52 redirecting userspace tool ioctls to the appropriate driver." 53 54- Matt Domsch, (Matt_Domsch@dell.com), 02.25.2004 LKML 55 56Design 57------ 58 59The Common Management Module is implemented in megaraid_mm.[ch] files. This 60module acts as a registry for low level hba drivers. The low level drivers 61(currently only megaraid) register each controller with the common module. 62 63The applications interface with the common module via the character device 64node exported by the module. 65 66The lower level drivers now understand only a new improved ioctl packet called 67uioc_t. The management module converts the older ioctl packets from the older 68applications into uioc_t. After driver handles the uioc_t, the common module 69will convert that back into the old format before returning to applications. 70 71As new applications evolve and replace the old ones, the old packet format 72will be retired. 73 74Common module dedicates one uioc_t packet to each controller registered. This 75can easily be more than one. But since megaraid is the only low level driver 76today, and it can handle only one ioctl, there is no reason to have more. But 77as new controller classes get added, this will be tuned appropriately. 78