1*4882a593Smuzhiyun.. SPDX-License-Identifier: GPL-2.0 2*4882a593Smuzhiyun 3*4882a593Smuzhiyun========================================== 4*4882a593SmuzhiyunNotes on register bank usage in the kernel 5*4882a593Smuzhiyun========================================== 6*4882a593Smuzhiyun 7*4882a593SmuzhiyunIntroduction 8*4882a593Smuzhiyun------------ 9*4882a593Smuzhiyun 10*4882a593SmuzhiyunThe SH-3 and SH-4 CPU families traditionally include a single partial register 11*4882a593Smuzhiyunbank (selected by SR.RB, only r0 ... r7 are banked), whereas other families 12*4882a593Smuzhiyunmay have more full-featured banking or simply no such capabilities at all. 13*4882a593Smuzhiyun 14*4882a593SmuzhiyunSR.RB banking 15*4882a593Smuzhiyun------------- 16*4882a593Smuzhiyun 17*4882a593SmuzhiyunIn the case of this type of banking, banked registers are mapped directly to 18*4882a593Smuzhiyunr0 ... r7 if SR.RB is set to the bank we are interested in, otherwise ldc/stc 19*4882a593Smuzhiyuncan still be used to reference the banked registers (as r0_bank ... r7_bank) 20*4882a593Smuzhiyunwhen in the context of another bank. The developer must keep the SR.RB value 21*4882a593Smuzhiyunin mind when writing code that utilizes these banked registers, for obvious 22*4882a593Smuzhiyunreasons. Userspace is also not able to poke at the bank1 values, so these can 23*4882a593Smuzhiyunbe used rather effectively as scratch registers by the kernel. 24*4882a593Smuzhiyun 25*4882a593SmuzhiyunPresently the kernel uses several of these registers. 26*4882a593Smuzhiyun 27*4882a593Smuzhiyun - r0_bank, r1_bank (referenced as k0 and k1, used for scratch 28*4882a593Smuzhiyun registers when doing exception handling). 29*4882a593Smuzhiyun 30*4882a593Smuzhiyun - r2_bank (used to track the EXPEVT/INTEVT code) 31*4882a593Smuzhiyun 32*4882a593Smuzhiyun - Used by do_IRQ() and friends for doing irq mapping based off 33*4882a593Smuzhiyun of the interrupt exception vector jump table offset 34*4882a593Smuzhiyun 35*4882a593Smuzhiyun - r6_bank (global interrupt mask) 36*4882a593Smuzhiyun 37*4882a593Smuzhiyun - The SR.IMASK interrupt handler makes use of this to set the 38*4882a593Smuzhiyun interrupt priority level (used by local_irq_enable()) 39*4882a593Smuzhiyun 40*4882a593Smuzhiyun - r7_bank (current) 41