Physical memory start address for ARM cores
Russell King - ARM Linux
linux at arm.linux.org.uk
Mon May 11 14:40:44 PDT 2015
On Mon, May 11, 2015 at 08:47:21PM +0530, Bhaskara rao Budiredla wrote:
> Could you please confirm if ARM architecture mandates the physical
> memory start address to align with a MegaBye boundary (something like
> 0xXXX00000)? I am seeing Linux Kernel crash if I relax that
The ARM architecture doesn't, but we (the kernel) does restrict it for
the sake of cross-machine portability. See this comment in
* Find the start of physical memory. As we are executing
* without the MMU on, we are in the physical address space.
* We just need to get rid of any offset by aligning the
* This alignment is a balance between the requirements of
* different platforms - we have chosen 128MB to allow
* platforms which align the start of their physical memory
* to 128MB to use this feature, while allowing the zImage
* to be placed within the first 128MB of memory on other
* platforms. Increasing the alignment means we place
* stricter alignment requirements on the start of physical
* memory, but relaxing it means that we break people who
* are already placing their zImage in (eg) the top 64MB
* of this range.
We will never change this requirement, as changing it breaks existing
platforms, and that's not allowed.
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