linux-kernel - [PATCH 4.9 091/108] ARC: smp-boot: Decouple Non masters waiting API from jump to entry point

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Date:   Thu, 15 Jun 2017 19:53:37 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Vineet Gupta <vgupta@...opsys.com>,
        Sasha Levin <alexander.levin@...izon.com>
Subject: [PATCH 4.9 091/108] ARC: smp-boot: Decouple Non masters waiting API from jump to entry point

4.9-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Vineet Gupta <vgupta@...opsys.com>


[ Upstream commit bf02454a741b58682a82c314a9a46bed930ed2f7 ]

For run-on-reset SMP configs, non master cores call a routine which
waits until Master gives it a "go" signal (currently using a shared
mem flag). The same routine then jumps off the well known entry point of
all non Master cores i.e. @first_lines_of_secondary

This patch moves out the last part into one single place in early boot
code.

This is better in terms of absraction (the wait API only waits) and
returns, leaving out the "jump off to" part.

In actual implementation this requires some restructuring of the early
boot code as well as Master now jumps to BSS setup explicitly,
vs. falling thru into it before.

Technically this patch doesn't cause any functional change, it just
moves the ugly #ifdef'ry from assembly code to "C"

Signed-off-by: Vineet Gupta <vgupta@...opsys.com>
Signed-off-by: Sasha Levin <alexander.levin@...izon.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 arch/arc/kernel/head.S |   14 +++++++-------
 arch/arc/kernel/smp.c  |    6 ++++--
 2 files changed, 11 insertions(+), 9 deletions(-)

--- a/arch/arc/kernel/head.S
+++ b/arch/arc/kernel/head.S
@@ -71,14 +71,14 @@ ENTRY(stext)
 	GET_CPU_ID  r5
 	cmp	r5, 0
 	mov.nz	r0, r5
-#ifdef CONFIG_ARC_SMP_HALT_ON_RESET
-	; Non-Master can proceed as system would be booted sufficiently
-	jnz	first_lines_of_secondary
-#else
+	bz	.Lmaster_proceed
+
 	; Non-Masters wait for Master to boot enough and bring them up
-	jnz	arc_platform_smp_wait_to_boot
-#endif
-	; Master falls thru
+	; when they resume, tail-call to entry point
+	mov	blink, @first_lines_of_secondary
+	j	arc_platform_smp_wait_to_boot
+
+.Lmaster_proceed:
 #endif
 
 	; Clear BSS before updating any globals
--- a/arch/arc/kernel/smp.c
+++ b/arch/arc/kernel/smp.c
@@ -98,14 +98,16 @@ static void arc_default_smp_cpu_kick(int
 
 void arc_platform_smp_wait_to_boot(int cpu)
 {
+	/* for halt-on-reset, we've waited already */
+	if (IS_ENABLED(CONFIG_ARC_SMP_HALT_ON_RESET))
+		return;
+
 	while (wake_flag != cpu)
 		;
 
 	wake_flag = 0;
-	__asm__ __volatile__("j @first_lines_of_secondary	\n");
 }
 
-
 const char *arc_platform_smp_cpuinfo(void)
 {
 	return plat_smp_ops.info ? : "";