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

Jan Hoffmann jan at 3e8.eu
Tue Jan 31 14:52:49 PST 2023

Hi Robert,

On 2023-01-30 at 00:08, Robert Marko wrote:
> Shouldn't it be possible for the modem driver itself to be fixed
> instead of faking
> the PCI details?

This hack is definitely far from ideal, but I'm not sure if there is a 
better way to fix this.

Here are a few more details about the issue:

On the affected devices (so far, three users reported it on the VRX518 
thread in the forum [0]), the function call to turn on the "EMA" 
hardware unit in the vrx518_tc driver [1] fails with the error mentioned 
in the commit message.

I don't have any details about it, but this EMA unit is part of the data 
path (it is also referenced in the ltq-atm and ltq-ptm data path drivers 
for older Lantiq modems). If the EMA unit is not running, then at least 
the transmit data path doesn't work, and any packets the driver writes 
to the TX ring are not actually sent out by the device.

This is also reproducible on non-affected devices by calling tc_clkoff 
instead of tc_clkon in the vrx518_tc driver (i.e. disabling the hardware 
unit). The same issue also occurs on affected devices running vendor 
firmware, if the "magic" in the PCIe driver is disabled in the device 
tree. So this is not just a bug in the data path driver.


> Especially considering that now modem support is not self-contained
> and will require
> patching the DWC Qualcomm PCI driver forever.
> Regards,
> Robert


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