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

[Robert Marko]

On Sun, 5 Feb 2023 at 01:10, Jan Hoffmann <jan at 3e8.eu> wrote:
>
>
> Am 02.02.23 um 11:54 schrieb Robert Marko:
> > On Tue, 31 Jan 2023 at 23:52, Jan Hoffmann <jan at 3e8.eu> wrote:
> >>
> >> 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.
> >
> > I get the issue, however, I am failing to see how faking the PCI ID for the
> > root adaptor is magically solving that?
> > If that works, why can't you just patch the driver to stop looking for
> > the ancient
> > Lantiq ID?
>
> As far as I can see, the magic values don't appear anywhere in the DSL
> drivers. So it doesn't seem like there is an easy fix like that.
>
> To me this looks like whatever access to these values is being done,
> seems to happen in hardware (or firmware). Maybe there are some
> revisions or variants of the modem that don't like to cooperate with
> non-Lantiq SoCs.
>
> But in the end, I don't know with certainty what exactly is happening
> here, as about the only public information on these modems are the
> open-source drivers (including the magic hack in the PCIe driver which
> in its original form contains comments like "do some magic" without
> really explaining what it actually does).

Ok, I am now getting the issue, it's probably in the damn firmware.
I still really dont like the hack that we are gonna need to carry forever.

I would like for somebody else to chime in as well.

Regards,
Robert
>
> Regards,
> Jan
>
>
> >
> > Regards,
> > Robert
> >>
> >>
> >> Regards,
> >> Jan
> >>
> >>
> >>>
> >>> Especially considering that now modem support is not self-contained
> >>> and will require
> >>> patching the DWC Qualcomm PCI driver forever.
> >>>
> >>> Regards,
> >>> Robert
> >>
> >>
> >> [0]
> >> https://forum.openwrt.org/t/adding-support-for-vrx518-and-maybe-vrx320/55160
> >> [1]
> >> https://gitlab.com/prpl-foundation/intel/vrx518_tc_drv/-/blob/ugw-8.5.2/dcdp/tc_main.c#L112
>
>