linux/Documentation/scsi/megaraid.rst
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   1.. SPDX-License-Identifier: GPL-2.0
   2
   3==========================
   4Notes on 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