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Uboot-V2: ARM: towards a common start-arm.S

U-Boot-Users Nishanth Menon 2 participants 2 messages Mar 17, 2008 – Mar 18, 2008

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Nishanth Menon

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Hi Sascha,

I think we dont have a seperate list for uboot-v2, so, just wanted to know the opinion of having a single arch/arm/cpu/start-arm.S instead of multiple start-arm files. essentially providing hooks to arch,soc,board specific preinits can allow us to reuse major chunk of code.. I have attached a sample start-arm.S (modified from start-arm920t.S) as reference.

Do let me know your comments and view as to how the initial handling can be made abstract enough to plug into requirements of future SOCs, boards etc. I am looking not to mash in #ifdef ARCH_XYZ for each of the SOC implementation I plan on doing.

Regards,
Nishanth Menon
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#1 lore raw

Hi,

Quoted 3 lines · Nishanth Menon

Hi Sascha,

I think we dont have a seperate list for uboot-v2,

No we have not. This is the right place ;)

Quoted 7 lines

so, just wanted to
know the opinion of having a single arch/arm/cpu/start-arm.S instead of multiple start-arm files. essentially providing hooks to arch,soc,board specific preinits can allow us to reuse major chunk of code.. I have attached a sample start-arm.S (modified from start-arm920t.S) as reference.

Quoted 7 lines

Do let me know your comments and view as to how the initial handling can be made abstract enough to plug into requirements of future SOCs, boards etc. I am looking not to mash in #ifdef ARCH_XYZ for each of the SOC implementation I plan on doing.

Regards,
Nishanth Menon

It is my plan to unify the different start.S files anyway, so good idea ;)

I'll comment on a diff to current start-arm920t.S as it's easier to see what you actually changed.

Quoted 5 lines
arch/arm/cpu/start-arm920t.S +0 -0
index db52ad9..a2c9ecb 100644

arch/arm/cpu/start-arm920t.S line 33

Quoted 10 lines
arch/arm/cpu/start-arm920t.S +1 -5
@@ -29,11 +29,7 @@
  * @brief The very basic beginning of each CPU after reset
  *
  * @note
- * This reset code can be used at least for:
- *  - ARM920T
- *  - i.MX1
- *  - i.MX27
- *  - i.MX31
+ * This reset code can be used at least for All ARM platforms

I wouldn't say it works at least on all arm platforms, maybe for xscale it's easier to have a start-xscale.S, but I haven't looked into this very deeply. But for sure this code won't work on any non-arm platform.

Quoted 22 lines
arch/arm/cpu/start-arm920t.S +0 -0
  *
  * FIXME: Stop doxygen from parsing the text below

*/

arch/arm/cpu/start-arm920t.S +6 -9
@@ -134,32 +130,26 @@ reset:
 #ifdef ARCH_HAS_INIT_LOWLEVEL
 	bl arch_init_lowlevel
 #endif
-	/*
-	 * flush v4 I/D caches
-	 */
-	mov	r0, #0
-	mcr	p15, 0, r0, c7, c7, 0	/* flush v3/v4 cache */
-	mcr	p15, 0, r0, c8, c7, 0	/* flush v4 TLB */
-
-	/*
-	 * disable MMU stuff and caches
+#ifdef CONFIG_SOC_PRE_INIT
+	/* Do SOC specific initalization here
+	 * r0 contains the start address
+	 * This allows for SOC code to configure
+	 * based on current program execution context
+	 * E.g.: NOR boot Vs SDRAM boot.

arch/arm/cpu/start-arm920t.S reset: · line 142

Quoted 10 lines
arch/arm/cpu/start-arm920t.S +3 -6
 	 */
-	mrc	p15, 0, r0, c1, c0, 0
-	bic	r0, r0, #0x00002300	/* clear bits 13, 9:8 (--V- --RS) */
-	bic	r0, r0, #0x00000087	/* clear bits 7, 2:0 (B--- -CAM) */
-	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
+	mov r0,pc
+	bl soc_init_crit
+#endif	/* CONFIG_SOC_PRE_INIT */

We do not have any SoC specific init at the moment, but when you need it lets introduce it here.

Quoted 18 lines
arch/arm/cpu/start-arm920t.S +4 -4
 	/*
-	 * before relocating, we have to setup RAM timing
-	 * because memory timing is board-dependend, you will
-	 * find a lowlevel_init.S in your board directory.
+	 * we do sys-critical inits only at reboot,
+	 * not when booting from ram!
 	 */
 #ifndef CONFIG_SKIP_LOWLEVEL_INIT
-	bl	board_init_lowlevel
+	bl	cpu_init_crit
 #endif
 
+#ifndef CONFIG_SKIP_RELOCATE_UBOOT
 relocate:				/* relocate U-Boot to RAM	    */
 	adr	r0, _start		/* r0 <- current position of code   */
 	ldr	r1, _TEXT_BASE		/* test if we run from flash or RAM */

arch/arm/cpu/start-arm920t.S copy_loop: · line 170

Quoted 5 lines
arch/arm/cpu/start-arm920t.S +1 -0
@@ -176,6 +166,7 @@ copy_loop:
 	stmia	r1!, {r3-r10}		/* copy to   target address [r1]    */
 	cmp	r0, r2			/* until source end addreee [r2]    */
 	ble	copy_loop
+#endif	/* CONFIG_SKIP_RELOCATE_UBOOT */

No need to introduce this option. Look into the various board specific lowlevel-init.S. They all check whether we run from RAM or not, so all binaries can run from RAM or ROM without changes.
In case we run with start address == link address the relocation is skipped anyway.

Quoted 37 lines
arch/arm/cpu/start-arm920t.S +31 -0
 	/* Set up the stack						    */
 stack_setup:

@@ -199,6 +190,48 @@ clbss_l:str	r2, [r0]		/* clear loop...                    */
 
 _start_armboot:	.word start_uboot
 
+/*************************************************************************
+ *
+ * CPU_init_critical registers
+ *
+ * setup important registers
+ * setup memory timing
+ *
+ ************************************************************************/
+#ifndef CONFIG_SKIP_LOWLEVEL_INIT
+cpu_init_crit:
+	/*
+	 * flush v4 I/D caches
+	 */
+	mov	r0, #0
+	mcr	p15, 0, r0, c7, c7, 0	/* flush v3/v4 cache */
+	mcr	p15, 0, r0, c8, c7, 0	/* flush v4 TLB */
+
+	/*
+	 * disable MMU stuff and caches
+	 */
+	mrc	p15, 0, r0, c1, c0, 0
+	bic	r0, r0, #0x00002300	/* clear bits 13, 9:8 (--V- --RS) */
+	bic	r0, r0, #0x00000087	/* clear bits 7, 2:0 (B--- -CAM) */
+#ifdef CONFIG_ARM_ALIGN_ABRT
+	orr	r0, r0, #0x00000002	/* set bit 2 (A) Align */
+#endif
+#ifdef CONFIG_ARM_I_CACHE
+	orr	r0, r0, #0x00001000	/* set bit 12 (I) I-Cache */
+#endif
+	mcr	p15, 0, r0, c1, c0, 0
+

arch/arm/cpu/start-arm920t.S clbss_l:str r2, [r0] /* clear loop... */ · line 233

Quoted 10 lines
arch/arm/cpu/start-arm920t.S +10 -0
+	/*
+	 * before relocating, we have to setup RAM timing
+	 * because memory timing is board-dependent, you will
+	 * find a lowlevel_init.S in your board directory.
+	 */
+	mov	ip, lr
+	bl	board_init_lowlevel
+	mov	lr, ip
+	mov	pc, lr
+#endif /* CONFIG_SKIP_LOWLEVEL_INIT */

Do we really need the SKIP_LOWLEVEL_INIT option? It should be safe to run all times.

Sascha

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