[U-Boot] [PATCH 2/2] arm64: booti: allow to place kernel image anywhere in physical memory

[Masahiro Yamada]

Hi Tom,


2017-02-23 1:19 GMT+09:00 Tom Rini <trini at konsulko.com>:
> On Wed, Feb 22, 2017 at 11:34:26AM +0900, Masahiro Yamada wrote:
>
>> At first, the ARM64 Linux booting requirement recommended that the
>> kernel image be placed text_offset bytes from 2MB aligned base near
>> the start of usable system RAM because memory below that base address
>> was unusable at that time.
>>
>> This requirement was relaxed by Linux commit a7f8de168ace ("arm64:
>> allow kernel Image to be loaded anywhere in physical memory").
>> Since then, the bit 3 of the flags field indicates the tolerance
>> of the kernel physical placement.  If this bit is set, the 2MB
>> aligned base may be anywhere in physical memory.  For details, see
>> Documentation/arm64/booting.txt of Linux.
>>
>> The booti command should be also relaxed to not expect the kernel
>> image at the start of the system RAM.  Even when booting older
>> kernel versions, it still makes sense to have some space below the
>> kernel.  For example, some firmware may sit at the start of the
>> system RAM.
>>
>> After all, the most flexible way for booting the kernel is to respect
>> the original images->ep instead of gd->bd->bi_dram[0].start.  If
>> image->ep (which is the address given to the booti command) already
>> meets the address requirement, just use it.  If not, relocate the
>> kernel to the next 2MB aligned address.
>>
>> Signed-off-by: Masahiro Yamada <yamada.masahiro at socionext.com>
>> ---
>>
>>  cmd/booti.c | 6 +++++-
>>  1 file changed, 5 insertions(+), 1 deletion(-)
>>
>> diff --git a/cmd/booti.c b/cmd/booti.c
>> index f65f0e7..9408c34 100644
>> --- a/cmd/booti.c
>> +++ b/cmd/booti.c
>> @@ -11,6 +11,8 @@
>>  #include <image.h>
>>  #include <lmb.h>
>>  #include <mapmem.h>
>> +#include <linux/kernel.h>
>> +#include <linux/sizes.h>
>>
>>  DECLARE_GLOBAL_DATA_PTR;
>>
>> @@ -54,7 +56,9 @@ static int booti_setup(bootm_headers_t *images)
>>        * If we are not at the correct run-time location, set the new
>>        * correct location and then move the image there.
>>        */
>> -     dst = gd->bd->bi_dram[0].start + le64_to_cpu(ih->text_offset);
>> +     dst = images->ep - ih->text_offset;
>> +     dst = ALIGN(dst, SZ_2M);
>> +     dst += ih->text_offset;
>
> I think the code will be slightly more complex here but I would rather
> see us check for the presence of the flag which allows for us to
> relocate things rather than assume that we can always use the address
> provided, or round it up.  The 'contract' wwith the kernel previously
> said it must be from start of memory and I'd rather not change that.


At first, I tried this approach.

The problem (at least for me) is
commit a7f8de168ace is quite new; this is only included in Linux 4.5 and later.
Linux 4.4 LTS will be used on Socionext's products for a while.
However, I need to avoid the relocation of the kernel image.

The gd->bd->bi_dram[0].start points to the start of the DRAM.
Here, some firmware is sitting at the start of the DRAM.
To hide the head of the memory from Linux,
the memory node in the device tree is carved out.

If CONFIG_ARCH_FIXUP_FDT_MEMORY is not set,
U-Boot passes the memory node as-is to Linux.
As a result, the Image is placed out of the available memory region
specified by DT,
then Linux fails to boot.


Somehow I want to achieve,
"Even when booting older kernel versions, it still makes sense to have
some space below the
kernel.  For example, some firmware may sit at the start of the system RAM."


Perhaps, can we introduce a CONFIG
to enable/disable the relocation?
Or, any other good idea?



-- 
Best Regards
Masahiro Yamada