mirror of
https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git
synced 2024-08-26 19:00:25 +00:00
![Mauro Carvalho Chehab](/assets/img/avatar_default.png)
- Add a SPDX header; - Adjust document title to follow ReST style; - Add blank lines to make ReST markup happy - Add it to sh/index.rst. Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org> Link: https://lore.kernel.org/r/adf117cf1edd7f43cb839ff2800f4315dfbcce13.1592203650.git.mchehab+huawei@kernel.org Signed-off-by: Jonathan Corbet <corbet@lwn.net>
40 lines
1.5 KiB
ReStructuredText
40 lines
1.5 KiB
ReStructuredText
.. SPDX-License-Identifier: GPL-2.0
|
|
|
|
==========================================
|
|
Notes on register bank usage in the kernel
|
|
==========================================
|
|
|
|
Introduction
|
|
------------
|
|
|
|
The SH-3 and SH-4 CPU families traditionally include a single partial register
|
|
bank (selected by SR.RB, only r0 ... r7 are banked), whereas other families
|
|
may have more full-featured banking or simply no such capabilities at all.
|
|
|
|
SR.RB banking
|
|
-------------
|
|
|
|
In the case of this type of banking, banked registers are mapped directly to
|
|
r0 ... r7 if SR.RB is set to the bank we are interested in, otherwise ldc/stc
|
|
can still be used to reference the banked registers (as r0_bank ... r7_bank)
|
|
when in the context of another bank. The developer must keep the SR.RB value
|
|
in mind when writing code that utilizes these banked registers, for obvious
|
|
reasons. Userspace is also not able to poke at the bank1 values, so these can
|
|
be used rather effectively as scratch registers by the kernel.
|
|
|
|
Presently the kernel uses several of these registers.
|
|
|
|
- r0_bank, r1_bank (referenced as k0 and k1, used for scratch
|
|
registers when doing exception handling).
|
|
|
|
- r2_bank (used to track the EXPEVT/INTEVT code)
|
|
|
|
- Used by do_IRQ() and friends for doing irq mapping based off
|
|
of the interrupt exception vector jump table offset
|
|
|
|
- r6_bank (global interrupt mask)
|
|
|
|
- The SR.IMASK interrupt handler makes use of this to set the
|
|
interrupt priority level (used by local_irq_enable())
|
|
|
|
- r7_bank (current)
|