arm, arm926ejs: Add option CONFIG_SYS_EXCEPTION_VECTORS_HIGH

The V bit of the c1 register of CP15 should not be cleared on DA850
SoCs since they have no valid memory at 0x00000000. This patch
introduces a configuration option CONFIG_SYS_EXCEPTION_VECTORS_HIGH
that allows setting the correct value for the V bit.

Signed-off-by: Christian Riesch <christian.riesch@omicron.at>
Reported-by: Sughosh Ganu <urwithsughosh@gmail.com>
Cc: Albert Aribaud <albert.u.boot@aribaud.net>
Cc: Tom Rini <trini@ti.com>
Cc: Sughosh Ganu <urwithsughosh@gmail.com>
Cc: Heiko Schocher <hs@denx.de>

README

@@ -420,6 +420,12 @@ The following options need to be configured:
 		XWAY SoCs for booting from NOR flash. The U-Boot image needs to
 		be swapped if a flash programmer is used.
 
+- ARM options:
+		CONFIG_SYS_EXCEPTION_VECTORS_HIGH
+
+		Select high exception vectors of the ARM core, e.g., do not
+		clear the V bit of the c1 register of CP15.
+
 - Linux Kernel Interface:
 		CONFIG_CLOCKS_IN_MHZ
 

arch/arm/cpu/arm926ejs/start.S

@@ -372,8 +372,13 @@ flush_dcache:
 	 * disable MMU and D cache, and enable I cache
 	 */
 	mrc	p15, 0, r0, c1, c0, 0
-	bic	r0, r0, #0x00002300	/* clear bits 13, 9:8 (--V- --RS) */
+	bic	r0, r0, #0x00000300	/* clear bits 9:8 (---- --RS) */
 	bic	r0, r0, #0x00000087	/* clear bits 7, 2:0 (B--- -CAM) */
+#ifdef CONFIG_SYS_EXCEPTION_VECTORS_HIGH
+	orr	r0, r0, #0x00002000	/* set bit 13 (--V- ----) */
+#else
+	bic	r0, r0, #0x00002000	/* clear bit 13 (--V- ----) */
+#endif
 	orr	r0, r0, #0x00000002	/* set bit 2 (A) Align */
 	orr	r0, r0, #0x00001000	/* set bit 12 (I) I-Cache */
 	mcr	p15, 0, r0, c1, c0, 0

include/configs/da850evm.h

@@ -37,6 +37,7 @@
 #define CONFIG_ARM926EJS		/* arm926ejs CPU core */
 #define CONFIG_SOC_DA8XX		/* TI DA8xx SoC */
 #define CONFIG_SOC_DA850		/* TI DA850 SoC */
+#define CONFIG_SYS_EXCEPTION_VECTORS_HIGH
 #define CONFIG_SYS_CLK_FREQ		clk_get(DAVINCI_ARM_CLKID)
 #define CONFIG_SYS_OSCIN_FREQ		24000000
 #define CONFIG_SYS_TIMERBASE		DAVINCI_TIMER0_BASE

include/configs/enbw_cmc.h

@@ -40,6 +40,7 @@
 #define CONFIG_ARM926EJS		/* arm926ejs CPU core */
 #define CONFIG_SOC_DA8XX		/* TI DA8xx SoC */
 #define CONFIG_SOC_DA850		/* TI DA850 SoC */
+#define CONFIG_SYS_EXCEPTION_VECTORS_HIGH
 #define CONFIG_SYS_CLK_FREQ		clk_get(DAVINCI_ARM_CLKID)
 #define CONFIG_SYS_OSCIN_FREQ		24000000
 #define CONFIG_SYS_TIMERBASE		DAVINCI_TIMER0_BASE

include/configs/hawkboard.h

@@ -35,6 +35,7 @@
 #define CONFIG_ARM926EJS		/* arm926ejs CPU core */
 #define CONFIG_SOC_DA8XX		/* TI DA8xx SoC */
 #define CONFIG_SOC_DA850		/* TI DA850 SoC */
+#define CONFIG_SYS_EXCEPTION_VECTORS_HIGH
 #define CONFIG_SYS_CLK_FREQ		clk_get(DAVINCI_ARM_CLKID)
 #define CONFIG_SYS_OSCIN_FREQ		24000000
 #define CONFIG_SYS_TIMERBASE		DAVINCI_TIMER0_BASE