Re: [PATCH net] net: phy: microchip: force IRQ polling mode for lan88xx

[Fiona Klute]

Am 14.04.25 um 17:43 schrieb Andrew Lunn:
> On Mon, Apr 14, 2025 at 05:26:33PM +0200, Fiona Klute wrote:
> > With lan88xx based devices the lan78xx driver can get stuck in an
> > interrupt loop while bringing the device up, flooding the kernel log
> > with messages like the following:
> >
> > lan78xx 2-3:1.0 enp1s0u3: kevent 4 may have been dropped
> >
> > Removing interrupt support from the lan88xx PHY driver forces the
> > driver to use polling instead, which avoids the problem.
> >
> > The issue has been observed with Raspberry Pi devices at least since
> > 4.14 (see [1], bug report for their downstream kernel), as well as
> > with Nvidia devices [2] in 2020, where disabling polling was the
> > vendor-suggested workaround (together with the claim that phylib
> > changes in 4.9 made the interrupt handling in lan78xx incompatible).
> >
> > Iperf reports well over 900Mbits/sec per direction with client in
> > --dualtest mode, so there does not seem to be a significant impact on
> > throughput (lan88xx device connected via switch to the peer).
> >
> > [1] https://github.com/raspberrypi/linux/issues/2447
> > [2] https://forums.developer.nvidia.com/t/jetson-xavier-and-lan7800-problem/142134/11
> >
> > Link: https://lore.kernel.org/0901d90d-3f20-4a10-b680-9c978e04ddda@xxxxxxx
> > Signed-off-by: Fiona Klute <fiona.klute@xxxxxx>
> > Cc: kernel-list@xxxxxxxxxxxxxxx
> > Cc: stable@xxxxxxxxxxxxxxx
>
> Thanks for submitting this. Two nit picks:
>
> It needed a Fixes: tag. Probably:
>
> Fixes: 792aec47d59d ("add microchip LAN88xx phy driver")
Sure, will add that (and a comment) and resend. I wasn't sure if I
should add it if I can't pinpoint exactly where the problem was
introduced, and it looks like the interrupt handling was changed a bit
after.

Best regards,
Fiona