[PATCH 2/6] arm/imx6q: add core definitions and low-level debug uart
Russell King - ARM Linux
linux at arm.linux.org.uk
Sat Sep 17 07:59:41 EDT 2011
On Mon, Sep 12, 2011 at 03:14:41PM +0100, Russell King - ARM Linux wrote:
> On Mon, Sep 12, 2011 at 10:44:39AM +0200, Sascha Hauer wrote:
> > I vote to skip params_phys and initrd_phys now. Every recent bootloader
> > does not need them. As the i.MX6 is a new SoC, we have no reason to
> > handle legacy bootloaders.
>
> Can we stop this misunderstanding right now.
>
> It's NOT about legacy boot loaders. It's about the bootp code which
> allows an initrd to be packaged up together with a zImage file as one
> single file.
>
> That's used to be able to boot with an initrd on platforms which can
> only obtain one file from the boot media, and they specify where the
> parameters are expected to be (which can be solved by updating the
> code to use r2) and where to place the initrd image (which can't be
> solved as it would mean encoding memory information for every platform
> into the bootp code.)
>
> An example of a current boot loader which requires this: Simtec's Able
> boot loader.
Here's a patch to reduce the reliance of arch/arm/boot/bootp on having
a correct initrd image location passed from the platform Makefile.boot.
It doesn't get rid of it, as it's required if the platform does not
pass a valid value in r2 to the kernel.
Note - I have a new code for a platform (of the nommu variety) which
requires this to be able to boot. Also note that we're probably going
to have to find a way to make this work with DT too (if not then I may
be submitting this platform without DT any support.)
---
arch/arm/boot/bootp/init.S | 34 ++++++++++++++++++++++++++++++----
1 file changed, 30 insertions(+), 4 deletions(-)
diff --git a/arch/arm/boot/bootp/init.S b/arch/arm/boot/bootp/init.S
index 78b5080..d1cb5a9 100644
--- a/arch/arm/boot/bootp/init.S
+++ b/arch/arm/boot/bootp/init.S
@@ -16,6 +16,14 @@
* size immediately following the kernel, we could build this into
* a binary blob, and concatenate the zImage using the cat command.
*/
+
+#define ATAG_CORE 0x54410001
+#define ATAG_CORE_SIZE ((2*4 + 3*4) >> 2)
+#define ATAG_CORE_SIZE_EMPTY ((2*4) >> 2)
+
+#define ATAG_INITRD2 0x54420005
+#define ATAG_INITRD2_SIZE ((4*4) >> 2)
+
.section .start,#alloc,#execinstr
.type _start, #function
.globl _start
@@ -37,13 +45,31 @@ _start: add lr, pc, #-0x8 @ lr = current load addr
@ r8 = initrd end
@ r9 = param_struct address
+/*
+ * Check whether we were given a valid ATAG list from the boot loader.
+ * If it looks like a valid pointer, then use that rather than the
+ * hard-coded value.
+ */
+ tst r2, #3 @ aligned
+ bne 1f
+ ldr r10, [r2, #0] @ get first tag size
+ teq r10, #ATAG_CORE_SIZE
+ teqne r10, #ATAG_CORE_SIZE_EMPTY
+ bne 1f
+ ldr r10, [r2, #4] @ get first tag type
+ teq r10, r5 @ is it ATAG_CORE?
+ bne 1f
+ mov r9, r2
+ b taglist
+
+1: mov r2, r9 @ params for the kernel
ldr r10, [r9, #4] @ get first tag
teq r10, r5 @ is it ATAG_CORE?
/*
* If we didn't find a valid tag list, create a dummy ATAG_CORE entry.
*/
movne r10, #0 @ terminator
- movne r4, #2 @ Size of this entry (2 words)
+ movne r4, #ATAG_CORE_SIZE_EMPTY @ Size of this entry (2 words)
stmneia r9, {r4, r5, r10} @ Size, ATAG_CORE, terminator
/*
@@ -56,7 +82,7 @@ taglist: ldr r10, [r9, #0] @ tag length
addne r9, r9, r10, lsl #2
bne taglist
- mov r5, #4 @ Size of initrd tag (4 words)
+ mov r5, #ATAG_INITRD2_SIZE @ Size of initrd tag (4 words)
stmia r9, {r5, r6, r7, r8, r10}
b kernel_start @ call kernel
@@ -80,8 +106,8 @@ data: .word initrd_start @ source initrd address
.word initrd_phys @ destination initrd address
.word initrd_size @ initrd size
- .word 0x54410001 @ r5 = ATAG_CORE
- .word 0x54420005 @ r6 = ATAG_INITRD2
+ .word ATAG_CORE @ r5
+ .word ATAG_INITRD2 @ r6
.word initrd_phys @ r7
.word initrd_size @ r8
.word params_phys @ r9
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