Diffstat (limited to 'Documentation/scsi/megaraid.txt')
1 files changed, 70 insertions, 0 deletions
diff --git a/Documentation/scsi/megaraid.txt b/Documentation/scsi/megaraid.txt
new file mode 100644
@@ -0,0 +1,70 @@
+ Notes on Management Module
+Different classes of controllers from LSI Logic, accept and respond to the
+user applications in a similar way. They understand the same firmware control
+commands. Furthermore, the applications also can treat different classes of
+the controllers uniformly. Hence it is logical to have a single module that
+interefaces with the applications on one side and all the low level drivers
+on the other.
+The advantages, though obvious, are listed for completeness:
+ i. Avoid duplicate code from the low level drivers.
+ ii. Unburden the low level drivers from having to export the
+ character node device and related handling.
+ iii. Implement any policy mechanisms in one place.
+ iv. Applications have to interface with only module instead of
+ multiple low level drivers.
+Currently this module (called Common Management Module) is used only to issue
+ioctl commands. But this module is envisioned to handle all user space level
+interactions. So any 'proc', 'sysfs' implementations will be localized in this
+"Shared code in a third module, a "library module", is an acceptable
+solution. modprobe automatically loads dependent modules, so users
+running "modprobe driver1" or "modprobe driver2" would automatically
+load the shared library module."
+ - Jeff Garzik (firstname.lastname@example.org), 02.25.2004 LKML
+"As Jeff hinted, if your userspace<->driver API is consistent between
+your new MPT-based RAID controllers and your existing megaraid driver,
+then perhaps you need a single small helper module (lsiioctl or some
+better name), loaded by both mptraid and megaraid automatically, which
+handles registering the /dev/megaraid node dynamically. In this case,
+both mptraid and megaraid would register with lsiioctl for each
+adapter discovered, and lsiioctl would essentially be a switch,
+redirecting userspace tool ioctls to the appropriate driver."
+ - Matt Domsch, (Matt_Domsch@dell.com), 02.25.2004 LKML
+The Common Management Module is implemented in megaraid_mm.[ch] files. This
+module acts as a registry for low level hba drivers. The low level drivers
+(currently only megaraid) register each controller with the common module.
+The applications interface with the common module via the character device
+node exported by the module.
+The lower level drivers now understand only a new improved ioctl packet called
+uioc_t. The management module converts the older ioctl packets from the older
+applications into uioc_t. After driver handles the uioc_t, the common module
+will convert that back into the old format before returning to applications.
+As new applications evolve and replace the old ones, the old packet format
+will be retired.
+Common module dedicates one uioc_t packet to each controller registered. This
+can easily be more than one. But since megaraid is the only low level driver
+today, and it can handle only one ioctl, there is no reason to have more. But
+as new controller classes get added, this will be tuned appropriately.