| Vineet Gupta | bf90e1e | 2013-01-18 15:12:18 +0530 | [diff] [blame] | 1 | /* |
| 2 | * fpu.c - save/restore of Floating Point Unit Registers on task switch |
| 3 | * |
| 4 | * Copyright (C) 2004, 2007-2010, 2011-2012 Synopsys, Inc. (www.synopsys.com) |
| 5 | * |
| 6 | * This program is free software; you can redistribute it and/or modify |
| 7 | * it under the terms of the GNU General Public License version 2 as |
| 8 | * published by the Free Software Foundation. |
| 9 | */ |
| 10 | |
| 11 | #include <linux/sched.h> |
| 12 | #include <asm/switch_to.h> |
| 13 | |
| 14 | /* |
| 15 | * To save/restore FPU regs, simplest scheme would use LR/SR insns. |
| 16 | * However since SR serializes the pipeline, an alternate "hack" can be used |
| 17 | * which uses the FPU Exchange insn (DEXCL) to r/w FPU regs. |
| 18 | * |
| 19 | * Store to 64bit dpfp1 reg from a pair of core regs: |
| 20 | * dexcl1 0, r1, r0 ; where r1:r0 is the 64 bit val |
| 21 | * |
| 22 | * Read from dpfp1 into pair of core regs (w/o clobbering dpfp1) |
| 23 | * mov_s r3, 0 |
| 24 | * daddh11 r1, r3, r3 ; get "hi" into r1 (dpfp1 unchanged) |
| 25 | * dexcl1 r0, r1, r3 ; get "low" into r0 (dpfp1 low clobbered) |
| 26 | * dexcl1 0, r1, r0 ; restore dpfp1 to orig value |
| 27 | * |
| 28 | * However we can tweak the read, so that read-out of outgoing task's FPU regs |
| 29 | * and write of incoming task's regs happen in one shot. So all the work is |
| 30 | * done before context switch |
| 31 | */ |
| 32 | |
| 33 | void fpu_save_restore(struct task_struct *prev, struct task_struct *next) |
| 34 | { |
| 35 | unsigned int *saveto = &prev->thread.fpu.aux_dpfp[0].l; |
| 36 | unsigned int *readfrom = &next->thread.fpu.aux_dpfp[0].l; |
| 37 | |
| 38 | const unsigned int zero = 0; |
| 39 | |
| 40 | __asm__ __volatile__( |
| 41 | "daddh11 %0, %2, %2\n" |
| 42 | "dexcl1 %1, %3, %4\n" |
| 43 | : "=&r" (*(saveto + 1)), /* early clobber must here */ |
| 44 | "=&r" (*(saveto)) |
| 45 | : "r" (zero), "r" (*(readfrom + 1)), "r" (*(readfrom)) |
| 46 | ); |
| 47 | |
| 48 | __asm__ __volatile__( |
| 49 | "daddh22 %0, %2, %2\n" |
| 50 | "dexcl2 %1, %3, %4\n" |
| 51 | : "=&r"(*(saveto + 3)), /* early clobber must here */ |
| 52 | "=&r"(*(saveto + 2)) |
| 53 | : "r" (zero), "r" (*(readfrom + 3)), "r" (*(readfrom + 2)) |
| 54 | ); |
| 55 | } |