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

[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")

>  static int lan88xx_suspend(struct phy_device *phydev)
>  {
>  	struct lan88xx_priv *priv = phydev->priv;
> @@ -528,9 +487,6 @@ static struct phy_driver microchip_phy_driver[] = {
>  	.config_aneg	= lan88xx_config_aneg,
>  	.link_change_notify = lan88xx_link_change_notify,
>  
> -	.config_intr	= lan88xx_phy_config_intr,
> -	.handle_interrupt = lan88xx_handle_interrupt,
> -

Maybe add a comment somewhere around here that interrupts are broken,
so not supported. Developers frequently don't look at commit messages,
but are more likely to notice a comment.

Thanks
    Andrew

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