[PATCH 1/1] ARM: i.MX31: Add support for mx31moboard board

[Sascha Hauer]

On Fri, Feb 28, 2014 at 09:21:40AM +0100, Philippe Rétornaz wrote:
> Le 27/02/2014 21:36, Sascha Hauer a écrit :
> >On Thu, Feb 27, 2014 at 03:03:45PM +0100, Philippe Rétornaz wrote:
> >>+lwl-y += lowlevel.o
> >>+obj-y += mx31moboard.o
> >>diff --git a/arch/arm/boards/mx31moboard/env/boot/net b/arch/arm/boards/mx31moboard/env/boot/net
> >>new file mode 100644
> >>index 0000000..e81f2cd
> >>--- /dev/null
> >>+++ b/arch/arm/boards/mx31moboard/env/boot/net
> >>@@ -0,0 +1,3 @@
> >>+#!/bin/sh
> >>+
> >>+# No network card support on this board
> >
> >Are you sure you want to drop this? You could attach a USB ethernet
> >dongle.
> 
> Ok, I will remove this file.
> 
> >>diff --git a/arch/arm/boards/mx31moboard/env/boot/sd b/arch/arm/boards/mx31moboard/env/boot/sd
> >>new file mode 100644
> >>index 0000000..f96633f
> >>--- /dev/null
> >>+++ b/arch/arm/boards/mx31moboard/env/boot/sd
> >>@@ -0,0 +1,18 @@
> >>+#!/bin/sh
> >>+
> >>+if [ "$1" = menu ]; then
> >>+        boot-menu-add-entry "$0" "SD Boot"
> >>+        exit
> >>+fi
> >>+
> >>+global.bootm.image=/mnt/sd/boot/zImage
> >>+
> >>+if [ -e /mnt/sd/boot/oftree ]; then
> >>+	global.bootm.oftree=/mnt/sd/boot/oftree
> >>+fi
> >>+
> >>+if [ -e /mnt/sd/boot/initrd.img ]; then
> >>+	global.bootm.initrd=/mnt/sd/boot/initrd.img
> >>+fi
> >>+
> >>+global.linux.bootargs.dyn.root="root=/dev/mmcblk0p1 rootwait"
> >
> >Consider using bootloader spec entries, see
> >http://www.freedesktop.org/wiki/Specifications/BootLoaderSpec/
> >Basically you put a config file under /loader/entries/ in your rootfs.
> >The config file describes where your kernel/initrd/oftree is. Under
> >barebox you just have to 'boot mci0' without further configuration.
> 
> Seems nice, I'll have a look at it.
> 
> >>+void __bare_init __naked barebox_arm_reset_vector(void)
> >>+{
> >>+	uint32_t r;
> >>+
> >>+	arm_cpu_lowlevel_init();
> >>+
> >>+	/* Enable IPU Display interface */
> >>+	writel(1 << 6, MX31_IPU_CTRL_BASE_ADDR);
> >>+
> >>+	writel(0x074B0BF5, MX31_CCM_BASE_ADDR + MX31_CCM_CCMR);
> >>+
> >>+	asm volatile("1:\n\t"
> >>+			"SUBS %0, %0, #1	\n\t"
> >>+			"BNE  1b		\n\t"
> >>+			: : "r" (0x4000) : "cc");
> >
> >You can write a delay loop in c with:
> >
> >	volatile int c;
> >
> >	for (c = 0; c < 0x4000; c++)
> 
> Well, no, at least not on my toolchain. Because the volatile ask gcc to
> not optimize the variable, it then put it on the stack. But the stack
> pointer is not yet initialized, so it crashes. I've tried with a
> barrier() instead of the volatile, but it leads to the same assembly
> (which is not surprising). Here is the compiled code with your suggestion:
> 
>         ldr     r2, .L9+8
>         b       .L2
> .L3:
>         ldr     r3, [sp, #4]
>         add     r3, r3, #1
>         str     r3, [sp, #4]
> .L2:
>         ldr     r3, [sp, #4]
>         cmp     r3, r2
>         ble     .L3
> 
> With L9+8:
>         .word   16383
> 
> But the stack pointer is initialised only in barebox_arm_entry() which
> is called later. So I decided that a two instructions assembly loop was
> the simplest solution.

This may happen because the function gets too complex and gcc starts
using the stack in this case.

Try rewriting the lowlevel stuff as:

static void __noinline mx31_moboard_startup(void)
{
	/* Put setup here */
}

void __bare_init __naked barebox_arm_reset_vector(void)
{
	 arm_cpu_lowlevel_init();

	 arm_setup_stack(MX31_IRAM_BASE_ADDR + MX31_IRAM_SIZE - 12);

	 mx31_moboard_startup();
}

With this you can use the stack and should be on the safe side.

Sascha

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