[U-Boot] [PATCH v0 13/20] efi_loader: use proper device-paths for partitions

[Heinrich Schuchardt]

On 08/05/2017 04:35 PM, Rob Clark wrote:
> On Sat, Aug 5, 2017 at 10:28 AM, Mark Kettenis <mark.kettenis at xs4all.nl> wrote:
>>> Date: Sat, 5 Aug 2017 16:01:51 +0200 (CEST)
>>> From: Mark Kettenis <mark.kettenis at xs4all.nl>
>>>
>>> Unfortunately something in this patch series breaks things for me on a
>>> Banana Pi:
>>
>> And according to git bisect:
>>
>> 4e3e748a50fc3f43e20c7ff407184596d7c9a589 is the first bad commit
>> commit 4e3e748a50fc3f43e20c7ff407184596d7c9a589
>> Author: Peter Jones <pjones at redhat.com>
>> Date:   Wed Jun 21 16:39:02 2017 -0400
>>
>>     efi: add some more device path structures
>>
>>     Signed-off-by: Peter Jones <pjones at redhat.com>
>>     Signed-off-by: Rob Clark <robdclark at gmail.com>
> 
> 
> hmm, odd.. it is only adding some #define's and structs that are not
> used until a later commit..
> 
> although it does also make 'struct efi_device_path_mac_addr' __packed,
> which it should have been before.  Is this an armv7?  I wonder if we
> have some troubles with unaligned accesses on armv7 that we don't have
> on aarch64 (or maybe compiler isn't turning access to device-path
> nodes into byte accesses if it can't do unaligned accesses.  (The node
> in the device-path structure are byte-packed.)

http://infocenter.arm.com/help/index.jsp?topic=/com.arm.doc.faqs/ka15414.html

<cite>On older processors, such as ARM9 family based processors, an
unaligned load had to be synthesised in software.  Typically by doing a
series of small accesses, and combining the results. ... Unaligned
access support must be enabled by setting the SCTLR.A bit in the system
control coprocessor</cite>

Generally packing structures is not a good idea performance-wise. The
sequence of fields should be carefully chosen to fill up to powers of
two (2, 4 , 8).

Regards

Heinrich

> 
> addr2line the faulting address I guess should confirm that.  If this
> is the issue, it's going to be a bit sad since we'll have to do a lot
> of copying back/forth of efi_device_path ptrs to aligned addresses :-/
> 
> BR,
> -R
>