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

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Message-ID: <db6b47a1-1a6c-476e-a679-aac3e5117c68@gmx.de>
Date: Tue, 15 Apr 2025 13:42:33 +0200
From: Fiona Klute <fiona.klute@....de>
To: Andrew Lunn <andrew@...n.ch>
Cc: netdev@...r.kernel.org, Andrew Lunn <andrew+netdev@...n.ch>,
 Thangaraj Samynathan <Thangaraj.S@...rochip.com>,
 Rengarajan Sundararajan <Rengarajan.S@...rochip.com>,
 UNGLinuxDriver@...rochip.com, "David S . Miller" <davem@...emloft.net>,
 Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>,
 Paolo Abeni <pabeni@...hat.com>, linux-usb@...r.kernel.org,
 linux-kernel@...r.kernel.org, kernel-list@...pberrypi.com
Subject: Re: [PATCH net] net: phy: microchip: force IRQ polling mode for
 lan88xx

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@lunn.ch
>> Signed-off-by: Fiona Klute <fiona.klute@....de>
>> Cc: kernel-list@...pberrypi.com
>> Cc: stable@...r.kernel.org
>
> 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