MIPS: Simplify PTRACE_PEEKUSR for FPC_EIR

All architecturally defined bits in the FPU implementation register
are read only & unchanging. It contains some implementation-defined
bits but the architecture manual states "This bits are explicitly not
intended to be used for mode control functions" which seems to provide
justification for viewing the register as a whole as unchanging. This
being the case we can simply re-use the value we read at boot rather
than having to re-read it later, and avoid the complexity which that
read entails.

Signed-off-by: Paul Burton <paul.burton@imgtec.com>
Reviewed-by: Qais Yousef <qais.yousef@imgtec.com>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/6144/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

arch/mips/kernel/ptrace.c

@@ -501,44 +501,10 @@ long arch_ptrace(struct task_struct *child, long request,
 		case FPC_CSR:
 			tmp = child->thread.fpu.fcr31;
 			break;
-		case FPC_EIR: { /* implementation / version register */
-			unsigned int flags;
-#ifdef CONFIG_MIPS_MT_SMTC
-			unsigned long irqflags;
-			unsigned int mtflags;
-#endif /* CONFIG_MIPS_MT_SMTC */
-
-			preempt_disable();
-			if (!cpu_has_fpu) {
-				preempt_enable();
-				break;
-			}
-
-#ifdef CONFIG_MIPS_MT_SMTC
-			/* Read-modify-write of Status must be atomic */
-			local_irq_save(irqflags);
-			mtflags = dmt();
-#endif /* CONFIG_MIPS_MT_SMTC */
-			if (cpu_has_mipsmt) {
-				unsigned int vpflags = dvpe();
-				flags = read_c0_status();
-				__enable_fpu(FPU_AS_IS);
-				__asm__ __volatile__("cfc1\t%0,$0": "=r" (tmp));
-				write_c0_status(flags);
-				evpe(vpflags);
-			} else {
-				flags = read_c0_status();
-				__enable_fpu(FPU_AS_IS);
-				__asm__ __volatile__("cfc1\t%0,$0": "=r" (tmp));
-				write_c0_status(flags);
-			}
-#ifdef CONFIG_MIPS_MT_SMTC
-			emt(mtflags);
-			local_irq_restore(irqflags);
-#endif /* CONFIG_MIPS_MT_SMTC */
-			preempt_enable();
+		case FPC_EIR:
+			/* implementation / version register */
+			tmp = current_cpu_data.fpu_id;
 			break;
-		}
 		case DSP_BASE ... DSP_BASE + 5: {
 			dspreg_t *dregs;
 

arch/mips/kernel/ptrace32.c

@@ -127,46 +127,10 @@ long compat_arch_ptrace(struct task_struct *child, compat_long_t request,
 		case FPC_CSR:
 			tmp = child->thread.fpu.fcr31;
 			break;
-		case FPC_EIR: { /* implementation / version register */
-			unsigned int flags;
-#ifdef CONFIG_MIPS_MT_SMTC
-			unsigned int irqflags;
-			unsigned int mtflags;
-#endif /* CONFIG_MIPS_MT_SMTC */
-
-			preempt_disable();
-			if (!cpu_has_fpu) {
-				preempt_enable();
-				tmp = 0;
-				break;
-			}
-
-#ifdef CONFIG_MIPS_MT_SMTC
-			/* Read-modify-write of Status must be atomic */
-			local_irq_save(irqflags);
-			mtflags = dmt();
-#endif /* CONFIG_MIPS_MT_SMTC */
-
-			if (cpu_has_mipsmt) {
-				unsigned int vpflags = dvpe();
-				flags = read_c0_status();
-				__enable_fpu(FPU_AS_IS);
-				__asm__ __volatile__("cfc1\t%0,$0": "=r" (tmp));
-				write_c0_status(flags);
-				evpe(vpflags);
-			} else {
-				flags = read_c0_status();
-				__enable_fpu(FPU_AS_IS);
-				__asm__ __volatile__("cfc1\t%0,$0": "=r" (tmp));
-				write_c0_status(flags);
-			}
-#ifdef CONFIG_MIPS_MT_SMTC
-			emt(mtflags);
-			local_irq_restore(irqflags);
-#endif /* CONFIG_MIPS_MT_SMTC */
-			preempt_enable();
+		case FPC_EIR:
+			/* implementation / version register */
+			tmp = current_cpu_data.fpu_id;
 			break;
-		}
 		case DSP_BASE ... DSP_BASE + 5: {
 			dspreg_t *dregs;