1 .. SPDX-License-Identifier: GPL-2.0
2
3 ==========================================
4 Notes on register bank usage in the kernel
5 ==========================================
6
7 Introduction
8 ------------
9
10 The SH-3 and SH-4 CPU families traditionally i
11 bank (selected by SR.RB, only r0 ... r7 are ba
12 may have more full-featured banking or simply
13
14 SR.RB banking
15 -------------
16
17 In the case of this type of banking, banked re
18 r0 ... r7 if SR.RB is set to the bank we are i
19 can still be used to reference the banked regi
20 when in the context of another bank. The devel
21 in mind when writing code that utilizes these
22 reasons. Userspace is also not able to poke at
23 be used rather effectively as scratch register
24
25 Presently the kernel uses several of these reg
26
27 - r0_bank, r1_bank (referenced as k0 a
28 registers when doing exception handl
29
30 - r2_bank (used to track the EXPEVT/IN
31
32 - Used by do_IRQ() and friends
33 of the interrupt exception v
34
35 - r6_bank (global interrupt mask)
36
37 - The SR.IMASK interrupt handl
38 interrupt priority level (us
39
40 - r7_bank (current)
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