Why Broadcom is so difficult (Tp-link Cxxxx series routers)

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ctdeneen
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Joined: 22 Jan 2021
Posts: 2

PostPosted: Fri Jan 22, 2021 7:30    Post subject: Why Broadcom is so difficult (Tp-link Cxxxx series routers) Reply with quote
I have a TP-Link c5400v2 that uses a very old version of OpenWrt (OpenWrt Attitude Adjustment 12.09-rc1 r13176). I went over to OpenWrt to check for support but found a page explaining that dd-wrt has more support than OpenWrt when it comes to Broadcom.

DD-WRT has a license agreement and NDA in place with Broadcom that allow usage of better, proprietary, closed source wireless drivers (binary blobs) which they are not allowed to redistribute freely.

I also found a post here where someone discussed a donated Tp-Link router but Brain Slayer replied that getting wireless working was difficult. Finally, there's also a "WIP" on the router page for the C3200, C3150, and C2600 but I couldn't find references to new support in the repo.

I was curious as to the difficulty of working with these drivers, I assume there is an ABI and some info. Does Broadcom provide insufficient documentation and/or not offer much support? Is Broadcom overall a low quality wireless chipset?
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blkt
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Joined: 20 Jan 2019
Posts: 3160

PostPosted: Fri Jan 22, 2021 13:42    Post subject: Reply with quote
I have no experience with Tp-Link routers, but see Netgear R7800 or R9000 with Atheros and open drivers.
feliciano
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Location: Latin America

PostPosted: Fri Jan 22, 2021 18:25    Post subject: Re: Why Broadcom is so difficult (Tp-link Cxxxx series route Reply with quote
Welcome to the forum.

ctdeneen wrote:
DD-WRT has a license agreement and NDA in place with Broadcom that allow usage of better, proprietary, closed source wireless drivers (binary blobs) which they are not allowed to redistribute freely.


That quote is probably from the old days of K2.4 and/or K2.6 (and a lot of backstage by then, no longer valid). Nowadays, dd-wrt is facing the same closed-source dead-ends as other developers, and that's why many recent dual-radio broadcoms lack of 5GHz support, for instance.

ctdeneen wrote:
Is Broadcom overall a low quality wireless chipset?

I don't think so. They just don't want us to tamper with "their" equipments anymore, "for security reasons".

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ctdeneen
DD-WRT Novice


Joined: 22 Jan 2021
Posts: 2

PostPosted: Sat Jan 23, 2021 19:37    Post subject: Reply with quote
I used binwalk on the firmware to extract the JFFS2 root and it is OpenWrt Attitude Adjustment 12.09-rc1 but it appears to be a fork they have maintained through many routers (even recent models).

It looks like they just keep piling on or modifying this old version of OpenWrt

Code:

Source: /home/hd2/C5400v2/28Aug2019/boards/model_brcm_bcm470x/iplatform_branch/cloud_dev_branch_c5400/private/tddp
Architecture: model_brcm_bcm470x
Source: /home/hd2/C5400v2/28Aug2019/boards/model_brcm_bcm470x/iplatform_branch/cloud_dev_branch_c5400/opensource/util-linux


They use both tools that are from OpenWrt, like "nvram":
Code:
nvram set wl_frag="2346"
nvram set wl_rts="2346"


and tp-link's own tools like "wlan_nvram_init" which I tried to execute to see if there was a help section that lists the parameters (no good).
Code:
qemu-arm -E LD_LIBRARY_PATH=/fw/_fw.bin.extracted/jffs2-root/fs_1/lib -L fw/_fw.bin.extracted/jffs2-root/fs_1/ ./usr/bin/wlan_nvram_init


Shouldn't it be possible for someone to just use the provided binary and setup your own API that either calls the scripts or binaries to modify the settings as needed by dd-wrt?

So I guess the issue is that dd-wrt wouldn't want to use the binary blob bcm module(s) without permission and the inability to make changes beyond what the settings interface provided allows.
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