tegra2: Simplify tegra_start() boot path

The Tegra2 boot path is more complicated than it needs to be. Since we want
to move to building most of U-Boot with ARMv7 and only a small part with
ARMv4T (for AVP) it should be as simple as possible.

This makes tegra2_start() into a simple function which either does AVP
init or A9 init depending on which core is running it. Both cores now
following the same init path, beginning at _start, and the special Tegra2
boot path code is no longer required.

Only two files need to be built for ARMv4T, and this is handled in the
Tegra2 CPU Makefile.

Signed-off-by: Simon Glass <sjg@chromium.org>
Signed-off-by: Tom Warren <twarren@nvidia.com>

arch/arm/cpu/armv7/tegra2/Makefile

@@ -23,6 +23,11 @@
 # MA 02111-1307 USA
 #
 
+# The AVP is ARMv4T architecture so we must use special compiler
+# flags for any startup files it might use.
+CFLAGS_arch/arm/cpu/armv7/tegra2/ap20.o += -march=armv4t
+CFLAGS_arch/arm/cpu/armv7/tegra2/clock.o += -march=armv4t
+
 include $(TOPDIR)/config.mk
 
 LIB	=  $(obj)lib$(SOC).o

arch/arm/cpu/armv7/tegra2/ap20.c

@@ -31,7 +31,12 @@
 #include <asm/arch/scu.h>
 #include <common.h>
 
-u32 s_first_boot = 1;
+/* Returns 1 if the current CPU executing is a Cortex-A9, else 0 */
+static int ap20_cpu_is_cortexa9(void)
+{
+	u32 id = readb(NV_PA_PG_UP_BASE + PG_UP_TAG_0);
+	return id == (PG_UP_TAG_0_PID_CPU & 0xff);
+}
 
 void init_pllx(void)
 {
@@ -283,38 +288,37 @@ void init_pmc_scratch(void)
 	writel(CONFIG_SYS_BOARD_ODMDATA, &pmc->pmc_scratch20);
 }
 
-void cpu_start(void)
+void tegra2_start(void)
 {
 	struct pmux_tri_ctlr *pmt = (struct pmux_tri_ctlr *)NV_PA_APB_MISC_BASE;
 
-	/* enable JTAG */
-	writel(0xC0, &pmt->pmt_cfg_ctl);
+	/* If we are the AVP, start up the first Cortex-A9 */
+	if (!ap20_cpu_is_cortexa9()) {
+		/* enable JTAG */
+		writel(0xC0, &pmt->pmt_cfg_ctl);
 
-	if (s_first_boot) {
 		/*
-		 * Need to set this before cold-booting,
-		 *  otherwise we'll end up in an infinite loop.
-		 */
-		s_first_boot = 0;
-		cold_boot();
+		* If we are ARM7 - give it a different stack. We are about to
+		* start up the A9 which will want to use this one.
+		*/
+		asm volatile("ldr	sp, =%c0\n"
+			: : "i"(AVP_EARLY_BOOT_STACK_LIMIT));
+
+		start_cpu((u32)_start);
+		halt_avp();
+		/* not reached */
 	}
-}
 
-void tegra2_start()
-{
-	if (s_first_boot) {
-		/* Init Debug UART Port (115200 8n1) */
-		uart_init();
+	/* Init PMC scratch memory */
+	init_pmc_scratch();
 
-		/* Init PMC scratch memory */
-		init_pmc_scratch();
-	}
+	enable_scu();
 
-#ifdef CONFIG_ENABLE_CORTEXA9
-	/* take the mpcore out of reset */
-	cpu_start();
+	/* enable SMP mode and FW for CPU0, by writing to Auxiliary Ctl reg */
+	asm volatile(
+		"mrc	p15, 0, r0, c1, c0, 1\n"
+		"orr	r0, r0, #0x41\n"
+		"mcr	p15, 0, r0, c1, c0, 1\n");
 
-	/* configure cache */
-	cache_configure();
-#endif
+	/* FIXME: should have ap20's L2 disabled too? */
 }

arch/arm/cpu/armv7/tegra2/ap20.h

@@ -102,3 +102,6 @@ void uart_init(void);
 void udelay(unsigned long);
 void cold_boot(void);
 void cache_configure(void);
+
+/* This is the main entry into U-Boot, used by the Cortex-A9 */
+extern void _start(void);