[PATCHv4] arm: socfpga: fix fetching cpu1start_addr for SMP

[dinguyen at opensource.altera.com]

From: Dinh Nguyen <dinguyen at opensource.altera.com>

When CPU1 is brought out of reset, it's MMU is not turned on yet, so it will
only be able to use physical addresses. For systems with that have the
MMU page configured for 0xC0000000, 0x80000000, or 0x40000000
"BIC 0x40000000" will work just fine, as it was just converting the
virtual address of &cpu1start_addr into a physical address, ie. 0xC0000000
became 0x80000000. So for systems where the SDRAM controller was able to do a
wrap-around access, this was working fine, as it was just dropping the MSB,
but for systems where out of bounds memory access is not allowed, this would
not allow CPU1 to correctly fetch &cpu1start_addr.

This patch fixes the secondary_trampoline code to correctly fetch the
physical address of cpu1start_addr directly. The patch will subtract the
correct PAGE_OFFSET from &cpu1start_addr. And since on this platform, the
physical memory will always start at 0x0, subtracting PAGE_OFFSET from
&cpu1start_addr will allow CPU1 to correctly fetch the value of cpu1start_addr.

While at it, change the name of cpu1start_addr to socfpga_cpu1start_addr
to avoid any future naming collisions for multiplatform image.

Signed-off-by: Dinh Nguyen <dinguyen at opensource.altera.com>
---
v4: Updated commit log to correctly lay out the usage of PAGE_OFFSET and
    add comments to the same effect.
v3: Used PAGE_OFFSET to get the physical address
v2: Correctly get the physical address instead of just a BIC hack.
---
 arch/arm/mach-socfpga/core.h    |  2 +-
 arch/arm/mach-socfpga/headsmp.S | 25 +++++++++++++++----------
 arch/arm/mach-socfpga/platsmp.c |  5 +++--
 arch/arm/mach-socfpga/socfpga.c |  4 ++--
 4 files changed, 21 insertions(+), 15 deletions(-)

diff --git a/arch/arm/mach-socfpga/core.h b/arch/arm/mach-socfpga/core.h
index 572b8f7..60c443d 100644
--- a/arch/arm/mach-socfpga/core.h
+++ b/arch/arm/mach-socfpga/core.h
@@ -40,7 +40,7 @@ extern void __iomem *rst_manager_base_addr;
 extern struct smp_operations socfpga_smp_ops;
 extern char secondary_trampoline, secondary_trampoline_end;
 
-extern unsigned long cpu1start_addr;
+extern unsigned long socfpga_cpu1start_addr;
 
 #define SOCFPGA_SCU_VIRT_BASE   0xfffec000
 
diff --git a/arch/arm/mach-socfpga/headsmp.S b/arch/arm/mach-socfpga/headsmp.S
index 95c115d..f65ea0a 100644
--- a/arch/arm/mach-socfpga/headsmp.S
+++ b/arch/arm/mach-socfpga/headsmp.S
@@ -9,21 +9,26 @@
  */
 #include <linux/linkage.h>
 #include <linux/init.h>
+#include <asm/memory.h>
 
 	.arch	armv7-a
 
 ENTRY(secondary_trampoline)
-	movw	r2, #:lower16:cpu1start_addr
-	movt  r2, #:upper16:cpu1start_addr
-
-	/* The socfpga VT cannot handle a 0xC0000000 page offset when loading
-		the cpu1start_addr, we bit clear it. Tested on HW and VT. */
-	bic	r2, r2, #0x40000000
-
-	ldr	r0, [r2]
-	ldr	r1, [r0]
-	bx	r1
+	/* CPU1 will always fetch from 0x0 when it is brought out of reset.
+	 * Thus, we can just subtract the PAGE_OFFSET to get the physical
+	 * address of &cpu1start_addr. This would not work for platforms
+	 * where the physical memory does not start at 0x0.
+	 */
+	adr	r0, 1f
+	ldmia	r0, {r1, r2}
+	sub	r2, r2, #PAGE_OFFSET
+	ldr	r3, [r2]
+	ldr	r4, [r3]
+	bx	r4
 
+	.align
+1:	.long	.
+	.long	socfpga_cpu1start_addr
 ENTRY(secondary_trampoline_end)
 
 ENTRY(socfpga_secondary_startup)
diff --git a/arch/arm/mach-socfpga/platsmp.c b/arch/arm/mach-socfpga/platsmp.c
index 5356a72..ba84c58 100644
--- a/arch/arm/mach-socfpga/platsmp.c
+++ b/arch/arm/mach-socfpga/platsmp.c
@@ -33,11 +33,12 @@ static int socfpga_boot_secondary(unsigned int cpu, struct task_struct *idle)
 {
 	int trampoline_size = &secondary_trampoline_end - &secondary_trampoline;
 
-	if (cpu1start_addr) {
+	if (socfpga_cpu1start_addr) {
 		memcpy(phys_to_virt(0), &secondary_trampoline, trampoline_size);
 
 		__raw_writel(virt_to_phys(socfpga_secondary_startup),
-			(sys_manager_base_addr + (cpu1start_addr & 0x000000ff)));
+			(sys_manager_base_addr + (socfpga_cpu1start_addr
+						  & 0x000000ff)));
 
 		flush_cache_all();
 		smp_wmb();
diff --git a/arch/arm/mach-socfpga/socfpga.c b/arch/arm/mach-socfpga/socfpga.c
index adbf383..383d61e 100644
--- a/arch/arm/mach-socfpga/socfpga.c
+++ b/arch/arm/mach-socfpga/socfpga.c
@@ -29,7 +29,7 @@
 void __iomem *socfpga_scu_base_addr = ((void __iomem *)(SOCFPGA_SCU_VIRT_BASE));
 void __iomem *sys_manager_base_addr;
 void __iomem *rst_manager_base_addr;
-unsigned long cpu1start_addr;
+unsigned long socfpga_cpu1start_addr;
 
 static struct map_desc scu_io_desc __initdata = {
 	.virtual	= SOCFPGA_SCU_VIRT_BASE,
@@ -70,7 +70,7 @@ void __init socfpga_sysmgr_init(void)
 	np = of_find_compatible_node(NULL, NULL, "altr,sys-mgr");
 
 	if (of_property_read_u32(np, "cpu1-start-addr",
-			(u32 *) &cpu1start_addr))
+			(u32 *) &socfpga_cpu1start_addr))
 		pr_err("SMP: Need cpu1-start-addr in device tree.\n");
 
 	sys_manager_base_addr = of_iomap(np, 0);
-- 
2.0.3