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

[Paul D]

On 2023-04-25 16:12, Jan Hoffmann wrote:
> 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
> 
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Sometimes fixing silicon bugs is analogous to hacks. Seems like making 
the datapath work is... desirable.

/P