[PATCH] arm64: Documentation: clarify Image placement in physical RAM

[Ard Biesheuvel]

On 2 March 2015 at 14:20, Mark Rutland <mark.rutland at arm.com> wrote:
> On Mon, Mar 02, 2015 at 11:48:55AM +0000, Ard Biesheuvel wrote:
>> The early init code maps the kernel image using statically
>> allocated page tables. This means that we can only allow
>> Image to be placed such that we can map its entire static
>> footprint using a single table entry at all but the lowest
>> level. So update the documentation to reflect that the Image
>> should not cross a 512 MB boundary, which ensures the above
>> on both 4k and 64k pages kernels.
>>
>> Signed-off-by: Ard Biesheuvel <ard.biesheuvel at linaro.org>
>
> Acked-by: Mark Rutland <mark.rutland at arm.com>
>

Thanks.
Note that the text is still wrong wrt to the FDT:

"""
The device tree blob (dtb) must be placed on an 8-byte boundary within
the first 512 megabytes from the start of the kernel image [...]
"""

but perhaps we should discuss first if we want to relax the
requirement that it shares the same 512 MB aligned region with the
kernel.
(RFC patch sent out last Friday, but there are some caveats)

-- 
Ard.


>> ---
>>  Documentation/arm64/booting.txt | 5 +++--
>>  1 file changed, 3 insertions(+), 2 deletions(-)
>>
>> diff --git a/Documentation/arm64/booting.txt b/Documentation/arm64/booting.txt
>> index f3c05b5f9f08..728de8b9116c 100644
>> --- a/Documentation/arm64/booting.txt
>> +++ b/Documentation/arm64/booting.txt
>> @@ -113,8 +113,9 @@ The Image must be placed text_offset bytes from a 2MB aligned base
>>  address near the start of usable system RAM and called there. Memory
>>  below that base address is currently unusable by Linux, and therefore it
>>  is strongly recommended that this location is the start of system RAM.
>> -At least image_size bytes from the start of the image must be free for
>> -use by the kernel.
>> +The physical memory region consisting of image_size bytes counting from
>> +the start of the image must be free for use by the kernel, and must not
>> +cross a 512 MB physical alignment boundary.
>>
>>  Any memory described to the kernel (even that below the 2MB aligned base
>>  address) which is not marked as reserved from the kernel e.g. with a
>> --
>> 1.8.3.2
>>
>>