Patches
Patches must be prepared against a specific version of the kernel (typically the current mainline version) - but sometimes, it's necessary to create a patch against linux-next, -mm or a subsystem tree.
Complex modification or additions of functionality should be submitted as a series of patches.
Use scripts/checkpatch.pl to verify the format of a patch.
Mailing patches
Patches should always be sent in plain text format.
Subject line
[PATCH nn/mm] subsys: one-line description of the patch where nn is a counter and mm the number of patches in a series and subsys is the name of the affected subsystem.
nn/mm can be omitted for single standalone patches.