[LEDE-DEV] [openwrt/openwrt] ar71xx: Ubiquiti Airmax M: add relocate-kernel to invalidate cache

Matthias Schiffer mschiffer at universe-factory.net
Thu Apr 26 13:10:59 PDT 2018

On 04/26/2018 09:22 PM, Etienne Champetier wrote:
> Hi Matthias,
> 2018-04-26 11:43 GMT-07:00 LEDE Commits <lede-commits at lists.infradead.org>:
>> neoraider pushed a commit to openwrt/openwrt.git, branch lede-17.01:
>> https://git.lede-project.org/eed9d40133fe6468cc253d0345c7d7332d2aaa7c
>> commit eed9d40133fe6468cc253d0345c7d7332d2aaa7c
>> Author: Matthias Schiffer <mschiffer at universe-factory.net>
>> AuthorDate: Thu Apr 26 20:04:48 2018 +0200
>>     ar71xx: Ubiquiti Airmax M: add relocate-kernel to invalidate cache
>>     Some Ubiquiti U-boot versions, in particular the "U-Boot
>>     (Jun 10 2015 - 10:54:50)" found with AirOS 5.6, do not correctly flush the
>>     caches for the whole kernel address range after decompressing the kernel
>>     image, leading to hard to debug boot failures, depending on kernel version
>>     and configuration.
>>     As a workaround, prepend the relocate-kernels loader, which will invalidate
>>     the caches after moving the kernel to the correct load address.
> So if I understand correctly,
> with this commit I don't need to downgrade my bullet M to v.5.5.10
> (U-Boot (Dec  5 2012 - 15:23:07))
> and I can just downgrade to v.5.6.x (U-Boot (Jun 10 2015
> - 10:54:50)) and maybe even the firsts 6.0.X (without the signed
> image)
> mtdparts differences between the 2 uboot version:
> https://community.ubnt.com/t5/airOS-SDK-Custom-Development/5-6-2-TFTP-ERROR/m-p/1310208/highlight/true#M2354

AFAIK, both AirOS 5.5 and 5.6 use the same flash layout. The mtdparts with
the EEPROM at 0x00730000 (also described in
https://wiki.openwrt.org/toh/ubiquiti/airmaxm ) is bogus and was not
directly caused by the newer Uboot or AirOS, but by installing "broken"
OpenWrt images (everything before [1]) from AirOS 5.6; the commit message
of [1] contains further details. Certain Uboot versions coming with 5.6
also did not unlock the flash chip, leading to unwritable flash on OpenWrt
(fixed in [2]).

The cache invalidation issue recently appeared after the update to kernel
4.4.120 in lede-17.01, but I'm not sure if the OpenWrt/LEDE default kernel
configuration is affected.

With these 3 fixes, installing OpenWrt from AirOS 5.6 should work fine; I
don't know about 6.0. It seems that I never backported [2] to lede-17.01
because it requires 2 other patches on kernel 4.4, but we have a downstream
patch for that in Gluon [3].



> Thanks
> Etienne

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