linux-kernel - [PATCH 4.9 092/108] ARCv2: smp-boot: wake_flag polling by non-Masters needs to be uncached

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Date:   Thu, 15 Jun 2017 19:53:38 +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 4.9 092/108] ARCv2: smp-boot: wake_flag polling by non-Masters needs to be uncached

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

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

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


[ Upstream commit 78f824d4312a8944f5340c6b161bba3bf2c81096 ]

This is needed on HS38 cores, for setting up IO-Coherency aperture properly

The polling could perturb the caches and coherecy fabric which could be
wrong in the small window when Master is setting up IOC aperture etc
in arc_cache_init()

We do it only for ARCv2 based builds to not affect EZChip ARCompact
based platform.

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/smp.c |   19 ++++++++++++++++---
 1 file changed, 16 insertions(+), 3 deletions(-)

--- a/arch/arc/kernel/smp.c
+++ b/arch/arc/kernel/smp.c
@@ -90,10 +90,23 @@ void __init smp_cpus_done(unsigned int m
  */
 static volatile int wake_flag;
 
+#ifdef CONFIG_ISA_ARCOMPACT
+
+#define __boot_read(f)		f
+#define __boot_write(f, v)	f = v
+
+#else
+
+#define __boot_read(f)		arc_read_uncached_32(&f)
+#define __boot_write(f, v)	arc_write_uncached_32(&f, v)
+
+#endif
+
 static void arc_default_smp_cpu_kick(int cpu, unsigned long pc)
 {
 	BUG_ON(cpu == 0);
-	wake_flag = cpu;
+
+	__boot_write(wake_flag, cpu);
 }
 
 void arc_platform_smp_wait_to_boot(int cpu)
@@ -102,10 +115,10 @@ void arc_platform_smp_wait_to_boot(int c
 	if (IS_ENABLED(CONFIG_ARC_SMP_HALT_ON_RESET))
 		return;
 
-	while (wake_flag != cpu)
+	while (__boot_read(wake_flag) != cpu)
 		;
 
-	wake_flag = 0;
+	__boot_write(wake_flag, 0);
 }
 
 const char *arc_platform_smp_cpuinfo(void)