[PATCH] ipq40xx: add PCIe magic hack to improve VRX518 compatibility

[Jan Hoffmann]

On 2023-01-30 at 23:40, Jan Hoffmann wrote:
> Some VRX518 modems fail to initialize properly with the error message
> "dc_ep_clk_on failed". As a result, the DSL data path doesn't work.
> 
> This hack, which is based on code from the FRITZ!Box 7530 GPL archive,
> fixes the issue. It changes the PCIe vendor/device ID to values matching
> a Lantiq SoC. It also appears to emulate a Lantiq CPU ID register for
> connected PCIe devices, by remapping the matching address area to a
> specially crafted buffer using the address translation unit.
> 
> The hack is only active if the "avm,host_magic" property is specified in
> the device tree, so this shouldn't affect any devices other than
> FRITZ!Box 7530/7520.
> 
> Signed-off-by: Jan Hoffmann <jan at 3e8.eu>


Is there any chance for this patch to get accepted?

I'm aware that this hack is not a particularly nice solution. And the 
additional maintenance burden of adding another kernel patch is also an 
obvious downside.

However, we don't know any better fix, and the modem just won't work 
without it on some devices. As there is no way to distinguish the 
affected devices externally, users will only find out if the modem on 
their device actually works after they installed OpenWrt on it. 
Recently, another user with this issue turned up on the forum [0].


Thanks,
Jan


[0] 
https://forum.openwrt.org/t/fritzbox-7520-wan-dsl0-7-device-is-missing/156424