powerpc: Don't handle ALTIVEC/SPE in ASM in _switch(). Do it in C.

_switch() saves and restores ALTIVEC and SPE status.
For altivec this is redundant with what __switch_to() does with
save_sprs() and restore_sprs() and giveup_all() before
calling _switch().

Add support for SPI in save_sprs() and restore_sprs() and
remove things from _switch().
Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/8ab21fd93d6e0047aa71e6509e5e312f14b2991b.1620998075.git.christophe.leroy@csgroup.eu

arch/powerpc/kernel/asm-offsets.c

@@ -116,7 +116,6 @@ int main(void)
 #ifdef CONFIG_ALTIVEC
 	OFFSET(THREAD_VRSTATE, thread_struct, vr_state.vr);
 	OFFSET(THREAD_VRSAVEAREA, thread_struct, vr_save_area);
-	OFFSET(THREAD_VRSAVE, thread_struct, vrsave);
 	OFFSET(THREAD_USED_VR, thread_struct, used_vr);
 	OFFSET(VRSTATE_VSCR, thread_vr_state, vscr);
 	OFFSET(THREAD_LOAD_VEC, thread_struct, load_vec);
@@ -147,7 +146,6 @@ int main(void)
 #ifdef CONFIG_SPE
 	OFFSET(THREAD_EVR0, thread_struct, evr[0]);
 	OFFSET(THREAD_ACC, thread_struct, acc);
-	OFFSET(THREAD_SPEFSCR, thread_struct, spefscr);
 	OFFSET(THREAD_USED_SPE, thread_struct, used_spe);
 #endif /* CONFIG_SPE */
 #endif /* CONFIG_PPC64 */

arch/powerpc/kernel/entry_32.S

@@ -176,28 +176,6 @@ _GLOBAL(_switch)
 	/* r3-r12 are caller saved -- Cort */
 	SAVE_NVGPRS(r1)
 	stw	r0,_NIP(r1)	/* Return to switch caller */
-	mfmsr	r11
-	li	r0,MSR_FP	/* Disable floating-point */
-#ifdef CONFIG_ALTIVEC
-BEGIN_FTR_SECTION
-	oris	r0,r0,MSR_VEC@h	/* Disable altivec */
-	mfspr	r12,SPRN_VRSAVE	/* save vrsave register value */
-	stw	r12,THREAD+THREAD_VRSAVE(r2)
-END_FTR_SECTION_IFSET(CPU_FTR_ALTIVEC)
-#endif /* CONFIG_ALTIVEC */
-#ifdef CONFIG_SPE
-BEGIN_FTR_SECTION
-	oris	r0,r0,MSR_SPE@h	 /* Disable SPE */
-	mfspr	r12,SPRN_SPEFSCR /* save spefscr register value */
-	stw	r12,THREAD+THREAD_SPEFSCR(r2)
-END_FTR_SECTION_IFSET(CPU_FTR_SPE)
-#endif /* CONFIG_SPE */
-	and.	r0,r0,r11	/* FP or altivec or SPE enabled? */
-	beq+	1f
-	andc	r11,r11,r0
-	mtmsr	r11
-	isync
-1:	stw	r11,_MSR(r1)
 	mfcr	r10
 	stw	r10,_CCR(r1)
 	stw	r1,KSP(r3)	/* Set old stack pointer */
@@ -218,19 +196,6 @@ END_FTR_SECTION_IFSET(CPU_FTR_SPE)
 	mr	r3,r2
 	addi	r2,r4,-THREAD	/* Update current */
 
-#ifdef CONFIG_ALTIVEC
-BEGIN_FTR_SECTION
-	lwz	r0,THREAD+THREAD_VRSAVE(r2)
-	mtspr	SPRN_VRSAVE,r0		/* if G4, restore VRSAVE reg */
-END_FTR_SECTION_IFSET(CPU_FTR_ALTIVEC)
-#endif /* CONFIG_ALTIVEC */
-#ifdef CONFIG_SPE
-BEGIN_FTR_SECTION
-	lwz	r0,THREAD+THREAD_SPEFSCR(r2)
-	mtspr	SPRN_SPEFSCR,r0		/* restore SPEFSCR reg */
-END_FTR_SECTION_IFSET(CPU_FTR_SPE)
-#endif /* CONFIG_SPE */
-
 	lwz	r0,_CCR(r1)
 	mtcrf	0xFF,r0
 	/* r3-r12 are destroyed -- Cort */

arch/powerpc/kernel/process.c

@@ -1129,6 +1129,10 @@ static inline void save_sprs(struct thread_struct *t)
 	if (cpu_has_feature(CPU_FTR_ALTIVEC))
 		t->vrsave = mfspr(SPRN_VRSAVE);
 #endif
+#ifdef CONFIG_SPE
+	if (cpu_has_feature(CPU_FTR_SPE))
+		t->spefscr = mfspr(SPRN_SPEFSCR);
+#endif
 #ifdef CONFIG_PPC_BOOK3S_64
 	if (cpu_has_feature(CPU_FTR_DSCR))
 		t->dscr = mfspr(SPRN_DSCR);
@@ -1159,6 +1163,11 @@ static inline void restore_sprs(struct thread_struct *old_thread,
 	    old_thread->vrsave != new_thread->vrsave)
 		mtspr(SPRN_VRSAVE, new_thread->vrsave);
 #endif
+#ifdef CONFIG_SPE
+	if (cpu_has_feature(CPU_FTR_SPE) &&
+	    old_thread->spefscr != new_thread->spefscr)
+		mtspr(SPRN_SPEFSCR, new_thread->spefscr);
+#endif
 #ifdef CONFIG_PPC_BOOK3S_64
 	if (cpu_has_feature(CPU_FTR_DSCR)) {
 		u64 dscr = get_paca()->dscr_default;