[OpenWrt-Devel] [PATCH 2/3] ath79: fix IMAGE_SIZE for common TP-Link definitions

[Tom Psyborg]

Correct me if I'm wrong but I thought all the data beyond IMAGE_SIZE
remain intact by OpenWrt on firstboot. Experimenting with Archer C7 v1
recently I was able to flash OpenWrt image (ar71xx) and after
reflashing tplink fw previous settings were still valid indicating
config partition hasn't been overwritten.
At least TL-MR22U has config partition of 64KB and Archer C7 has 128KB
- I've gone through GPL sources of Archer and it seems between two
firmware versions this partition was increased from 64 to 128KB,
actually I discovered this by hexdiff-ing u-boot versions from each
firmware version

On 07/08/2019, Adrian Schmutzler <mail at adrianschmutzler.de> wrote:
>> -----Original Message-----
>> From: openwrt-devel [mailto:openwrt-devel-bounces at lists.openwrt.org] On
>> Behalf Of Tom Psyborg
>> Sent: Mittwoch, 7. August 2019 17:58
>> To: Adrian Schmutzler <freifunk at adrianschmutzler.de>
>> Cc: openwrt-devel at lists.openwrt.org
>> Subject: Re: [OpenWrt-Devel] [PATCH 2/3] ath79: fix IMAGE_SIZE for common
>> TP-Link definitions
>>
>> Hi
>>
>> Looks like there were many doubts about image size over the years.
>>
>> One thing that should be considered is use of OEM firmware, either in
>> case of just a single revert after OpenWrt flashing, or multiple
>> reverts/switching between OEM/OpenWrt firmwares.
>>
>> Relevant in this case is config partition within OEM fw, and by
>> specifying OpenWrt image size to occupy all available flash space
>> between u-boot and art partitions destroys config contents which may
>> turn up very impractical for those that do frequent switching between
>> the two.
>>
>> Further, config partition size also varies from device to device, some
>> have it 64KB others 128KB in size, at least what I observed with my
>> devices.
>>
>> So, the correct image size for Archer C7 v1 turned out to be 0x7b0000
>
> But wouldn't this call for introducing a config partition for the C7 v1?
> I'm not sure how your analysis is affecting the IMAGE_SIZE discussion
> (unless you say TP-Link devices generally have this config partition with
> different sizes, and thus the whole concept of including IMAGE_SIZE in
> common definitions is "wrong")...
>
> Best
>
> Adrian
>

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