linux-kernel - [PATCH 3/3] arm: zynq: slcr: Use read-modify-write for register writes

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Date:	Wed, 17 Jul 2013 10:10:15 -0700
From:	Soren Brinkmann <soren.brinkmann@...inx.com>
To:	Michal Simek <michal.simek@...inx.com>,
	Russell King <linux@....linux.org.uk>
Cc:	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	Soren Brinkmann <soren.brinkmann@...inx.com>
Subject: [PATCH 3/3] arm: zynq: slcr: Use read-modify-write for register writes

zynq_slcr_cpu_start/stop() ignored the current register state when
writing to a register. Fixing this by implementing proper
read-modify-write.

Signed-off-by: Soren Brinkmann <soren.brinkmann@...inx.com>
---
 arch/arm/mach-zynq/slcr.c | 16 ++++++++--------
 1 file changed, 8 insertions(+), 8 deletions(-)

diff --git a/arch/arm/mach-zynq/slcr.c b/arch/arm/mach-zynq/slcr.c
index 44a4ab6..1836d5a 100644
--- a/arch/arm/mach-zynq/slcr.c
+++ b/arch/arm/mach-zynq/slcr.c
@@ -61,11 +61,11 @@ void zynq_slcr_system_reset(void)
  */
 void zynq_slcr_cpu_start(int cpu)
 {
-	/* enable CPUn */
-	writel(SLCR_A9_CPU_CLKSTOP << cpu,
-	       zynq_slcr_base + SLCR_A9_CPU_RST_CTRL_OFFSET);
-	/* enable CLK for CPUn */
-	writel(0x0 << cpu, zynq_slcr_base + SLCR_A9_CPU_RST_CTRL_OFFSET);
+	u32 reg = readl(zynq_slcr_base + SLCR_A9_CPU_RST_CTRL_OFFSET);
+	reg &= ~(SLCR_A9_CPU_RST << cpu);
+	writel(reg, zynq_slcr_base + SLCR_A9_CPU_RST_CTRL_OFFSET);
+	reg &= ~(SLCR_A9_CPU_CLKSTOP << cpu);
+	writel(reg, zynq_slcr_base + SLCR_A9_CPU_RST_CTRL_OFFSET);
 }
 
 /**
@@ -74,9 +74,9 @@ void zynq_slcr_cpu_start(int cpu)
  */
 void zynq_slcr_cpu_stop(int cpu)
 {
-	/* stop CLK and reset CPUn */
-	writel((SLCR_A9_CPU_CLKSTOP | SLCR_A9_CPU_RST) << cpu,
-	       zynq_slcr_base + SLCR_A9_CPU_RST_CTRL_OFFSET);
+	u32 reg = readl(zynq_slcr_base + SLCR_A9_CPU_RST_CTRL_OFFSET);
+	reg |= (SLCR_A9_CPU_CLKSTOP | SLCR_A9_CPU_RST) << cpu;
+	writel(reg, zynq_slcr_base + SLCR_A9_CPU_RST_CTRL_OFFSET);
 }
 
 /**
-- 
1.8.3.3

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