linux-kernel - [PATCH v6] powerpc/irq: inline call_do_irq() and call_do

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Date:   Fri, 19 Mar 2021 06:34:43 +0000 (UTC)
From:   Christophe Leroy <christophe.leroy@...roup.eu>
To:     Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Michael Ellerman <mpe@...erman.id.au>
Cc:     linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org
Subject: [PATCH v6] powerpc/irq: inline call_do_irq() and call_do_softirq() on
 PPC32

call_do_irq() and call_do_softirq() are simple enough to be
worth inlining.

Inlining them avoids an mflr/mtlr pair plus a save/reload on stack.
It also allows GCC to keep the saved ksp_limit in an nonvolatile reg.

This is inspired from S390 arch. Several other arches do more or
less the same. The way sparc arch does seems odd thought.

For the time being this is limited to PPC32 because there are
incertainties on the handling of r2 which is the TOC on PPC64,
see discussion at https://patchwork.ozlabs.org/patch/1174288/

Signed-off-by: Christophe Leroy <christophe.leroy@...roup.eu>
Reviewed-by: Segher Boessenkool <segher@...nel.crashing.org>
---
v2: no change.
v3: no change.
v4:
- comment reminding the purpose of the inline asm block.
- added r2 as clobbered reg
v5:
- Limiting the change to PPC32 for now.
- removed r2 from the clobbered regs list (on PPC32 r2 points to current all the time)
- Removed patch 1 and merged ksp_limit handling in here.
v6:
- Rebase on top of merge-test (ca6e327fefb2).
- Remove the ksp_limit stuff as it's doesn't exist anymore.
---
 arch/powerpc/include/asm/irq.h |  2 ++
 arch/powerpc/kernel/irq.c      | 34 ++++++++++++++++++++++++++++++++++
 arch/powerpc/kernel/misc_32.S  | 25 -------------------------
 3 files changed, 36 insertions(+), 25 deletions(-)

diff --git a/arch/powerpc/include/asm/irq.h b/arch/powerpc/include/asm/irq.h
index f3f264e441a7..23c28974ca29 100644
--- a/arch/powerpc/include/asm/irq.h
+++ b/arch/powerpc/include/asm/irq.h
@@ -53,8 +53,10 @@ extern void *mcheckirq_ctx[NR_CPUS];
 extern void *hardirq_ctx[NR_CPUS];
 extern void *softirq_ctx[NR_CPUS];
 
+#ifdef CONFIG_PPC64
 void call_do_softirq(void *sp);
 void call_do_irq(struct pt_regs *regs, void *sp);
+#endif
 extern void do_IRQ(struct pt_regs *regs);
 extern void __init init_IRQ(void);
 extern void __do_irq(struct pt_regs *regs);
diff --git a/arch/powerpc/kernel/irq.c b/arch/powerpc/kernel/irq.c
index 5b72abbff96c..327422c57ae8 100644
--- a/arch/powerpc/kernel/irq.c
+++ b/arch/powerpc/kernel/irq.c
@@ -667,6 +667,40 @@ static inline void check_stack_overflow(void)
 	}
 }
 
+#ifdef CONFIG_PPC32
+static inline void call_do_softirq(const void *sp)
+{
+	register unsigned long ret asm("r3");
+
+	/* Temporarily switch r1 to sp, call __do_softirq() then restore r1. */
+	asm volatile(
+		"	"PPC_STLU"	1, %2(%1);\n"
+		"	mr		1, %1;\n"
+		"	bl		%3;\n"
+		"	"PPC_LL"	1, 0(1);\n" :
+		"=r"(ret) :
+		"b"(sp), "i"(THREAD_SIZE - STACK_FRAME_OVERHEAD), "i"(__do_softirq) :
+		"lr", "xer", "ctr", "memory", "cr0", "cr1", "cr5", "cr6", "cr7",
+		"r0", "r4", "r5", "r6", "r7", "r8", "r9", "r10", "r11", "r12");
+}
+
+static inline void call_do_irq(struct pt_regs *regs, void *sp)
+{
+	register unsigned long r3 asm("r3") = (unsigned long)regs;
+
+	/* Temporarily switch r1 to sp, call __do_irq() then restore r1. */
+	asm volatile(
+		"	"PPC_STLU"	1, %2(%1);\n"
+		"	mr		1, %1;\n"
+		"	bl		%3;\n"
+		"	"PPC_LL"	1, 0(1);\n" :
+		"+r"(r3) :
+		"b"(sp), "i"(THREAD_SIZE - STACK_FRAME_OVERHEAD), "i"(__do_irq) :
+		"lr", "xer", "ctr", "memory", "cr0", "cr1", "cr5", "cr6", "cr7",
+		"r0", "r4", "r5", "r6", "r7", "r8", "r9", "r10", "r11", "r12");
+}
+#endif
+
 void __do_irq(struct pt_regs *regs)
 {
 	unsigned int irq;
diff --git a/arch/powerpc/kernel/misc_32.S b/arch/powerpc/kernel/misc_32.S
index acc410043b96..6a076bef2932 100644
--- a/arch/powerpc/kernel/misc_32.S
+++ b/arch/powerpc/kernel/misc_32.S
@@ -27,31 +27,6 @@
 
 	.text
 
-_GLOBAL(call_do_softirq)
-	mflr	r0
-	stw	r0,4(r1)
-	stwu	r1,THREAD_SIZE-STACK_FRAME_OVERHEAD(r3)
-	mr	r1,r3
-	bl	__do_softirq
-	lwz	r1,0(r1)
-	lwz	r0,4(r1)
-	mtlr	r0
-	blr
-
-/*
- * void call_do_irq(struct pt_regs *regs, void *sp);
- */
-_GLOBAL(call_do_irq)
-	mflr	r0
-	stw	r0,4(r1)
-	stwu	r1,THREAD_SIZE-STACK_FRAME_OVERHEAD(r4)
-	mr	r1,r4
-	bl	__do_irq
-	lwz	r1,0(r1)
-	lwz	r0,4(r1)
-	mtlr	r0
-	blr
-
 /*
  * This returns the high 64 bits of the product of two 64-bit numbers.
  */
-- 
2.25.0