Re: [PATCH net v2] net: phy: microchip: force IRQ polling mode for lan88xx

[Andrew Lunn]

On Wed, Apr 16, 2025 at 12:24:13PM +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
> Fixes: 792aec47d59d ("add microchip LAN88xx phy driver")
> Signed-off-by: Fiona Klute <fiona.klute@xxxxxx>
> Cc: kernel-list@xxxxxxxxxxxxxxx
> Cc: stable@xxxxxxxxxxxxxxx

Reviewed-by: Andrew Lunn <andrew@xxxxxxx>

    Andrew