[PATCH 08/14] powerpc/rtas: call enter_rtas in real-mode on 64-bit

[Nicholas Piggin]

This moves MSR save/restore and some real-mode juggling out of asm and
into C code, simplifying things.

Signed-off-by: Nicholas Piggin <npiggin at gmail.com>
---
 arch/powerpc/kernel/rtas.c       | 15 ++++++++++++---
 arch/powerpc/kernel/rtas_entry.S | 32 +++++---------------------------
 2 files changed, 17 insertions(+), 30 deletions(-)

diff --git a/arch/powerpc/kernel/rtas.c b/arch/powerpc/kernel/rtas.c
index 6b5892d6a56b..87ede1877816 100644
--- a/arch/powerpc/kernel/rtas.c
+++ b/arch/powerpc/kernel/rtas.c
@@ -47,13 +47,22 @@
 /* This is here deliberately so it's only used in this file */
 void enter_rtas(unsigned long);
 
-static inline void do_enter_rtas(unsigned long args)
+static noinline void do_enter_rtas(unsigned long args)
 {
 	BUG_ON(!irqs_disabled());
 
-	hard_irq_disable(); /* Ensure MSR[EE] is disabled on PPC64 */
+	if (IS_ENABLED(CONFIG_PPC64)) {
+		unsigned long msr;
 
-	enter_rtas(args);
+		hard_irq_disable();
+
+		msr = mfmsr();
+		mtmsr(msr & ~(MSR_IR|MSR_DR));
+		enter_rtas(args);
+		mtmsr(msr);
+	} else {
+		enter_rtas(args);
+	}
 
 	srr_regs_clobbered(); /* rtas uses SRRs, invalidate */
 }
diff --git a/arch/powerpc/kernel/rtas_entry.S b/arch/powerpc/kernel/rtas_entry.S
index 5f65ea4436c6..292551684bbd 100644
--- a/arch/powerpc/kernel/rtas_entry.S
+++ b/arch/powerpc/kernel/rtas_entry.S
@@ -84,14 +84,11 @@ _GLOBAL(enter_rtas)
 	li	r0,0
 	mtcr	r0
 
-	mfmsr	r6
-
-	/* Unfortunately, the stack pointer and the MSR are also clobbered,
-	 * so they are saved in the PACA which allows us to restore
-	 * our original state after RTAS returns.
+	/*
+	 * The stack pointer is clobbered, so it is saved in the PACA which
+	 * allows us to restore our original state after RTAS returns.
 	 */
 	std	r1,PACAR1(r13)
-	std	r6,PACASAVEDMSR(r13)
 
 	/* Setup our real return addr */
 	LOAD_REG_ADDR(r4,rtas_return_loc)
@@ -100,7 +97,6 @@ _GLOBAL(enter_rtas)
 
 	LOAD_REG_IMMEDIATE(r6, MSR_ME)
 
-__enter_rtas:
 	LOAD_REG_ADDR(r4, rtas)
 	ld	r5,RTASENTRY(r4)	/* get the rtas->entry value */
 	ld	r4,RTASBASE(r4)		/* get the rtas->base value */
@@ -112,6 +108,7 @@ __enter_rtas:
 	mtspr	SPRN_SRR1,r6
 	RFI_TO_KERNEL
 	b	.	/* prevent speculative execution */
+_ASM_NOKPROBE_SYMBOL(enter_rtas)
 
 rtas_return_loc:
 	FIXUP_ENDIAN
@@ -127,29 +124,10 @@ rtas_return_loc:
 	sync
 	mtmsrd	r6
 
-	/* relocation is off at this point */
 	GET_PACA(r13)
 
-	bcl	20,31,$+4
-0:	mflr	r3
-	ld	r3,(1f-0b)(r3)		/* get &rtas_restore_regs */
-
 	ld	r1,PACAR1(r13)		/* Restore our SP */
-	ld	r4,PACASAVEDMSR(r13)	/* Restore our MSR */
 
-	mtspr	SPRN_SRR0,r3
-	mtspr	SPRN_SRR1,r4
-	RFI_TO_KERNEL
-	b	.	/* prevent speculative execution */
-_ASM_NOKPROBE_SYMBOL(enter_rtas)
-_ASM_NOKPROBE_SYMBOL(__enter_rtas)
-_ASM_NOKPROBE_SYMBOL(rtas_return_loc)
-
-	.align	3
-1:	.8byte	rtas_restore_regs
-
-rtas_restore_regs:
-	/* relocation is on at this point */
 	REST_GPR(2, r1)			/* Restore the TOC */
 	REST_NVGPRS(r1)			/* Restore the non-volatiles */
 
@@ -169,5 +147,5 @@ rtas_restore_regs:
 
 	mtlr	r0
 	blr				/* return to caller */
-
+_ASM_NOKPROBE_SYMBOL(rtas_return_loc)
 #endif /* CONFIG_PPC32 */
-- 
2.23.0