On Wed, Aug 15, 2012 at 01:20:02PM +0000, Arnd Bergmann wrote:

On Tuesday 14 August 2012, Catalin Marinas wrote:

quoted

+The AArch64 exception model is made up of a number of exception levels
+(EL0 - EL3), with EL0 and EL1 having a secure and a non-secure
+counterpart.  EL2 is the hypervisor level and exists only in non-secure
+mode. EL3 is the highest priority level and exists only in secure mode.

I'm always confused by a description like this. It sounds like you cannot
have a hypervisor if you have code running in secure mode in EL3. What
I instead understand is that you enter non-secure mode by going from
EL3 into EL2.

quoted

+2. Setup the device tree
+-------------------------
+
+Requirement: MANDATORY
+
+The device tree blob (dtb) must be no bigger than 2 megabytes in size
+and placed at a 2-megabyte boundary within the first 512 megabytes from
+the start of the kernel image. This is to allow the kernel to map the
+blob using a single section mapping in the initial page tables.

I've seen people put firmware for some peripherals into the device tree,
so that a device driver can grab a blob from there and load it into the
device, rather than calling request_firmware() which would fail if the
OS running on the system does not contain the blob. If such firmware is
too large, you end up violating the 2 MB limit you impose here.

Should we keep that limit and declare those use cases as invalid, or
should we try to make the boot protocol more flexible?

quoted

diff --git a/arch/arm64/include/asm/setup.h b/arch/arm64/include/asm/setup.h
new file mode 100644
index 0000000..d766493
--- /dev/null
+++ b/arch/arm64/include/asm/setup.h

@@ -0,0 +1,26 @@
+#ifndef __ASM_SETUP_H
+#define __ASM_SETUP_H
+
+#include <linux/types.h>
+
+#define COMMAND_LINE_SIZE 1024
+
+#endif

Is this necessary? The asm-generic version of this file allows 512 bytes,
which seems plenty.

Chrome OS on my system today uses a 553 character cmdline, in particular
because some of the device mapper arguments are in there (since we boot without
ramdisk). It adds up quickly.

I suggest keeping it common with x86 since those limits are what people
will be used to (2048).


-Olof