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

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Message-ID: <89826aa3-adc6-4278-a85a-b72ba8132add@lunn.ch>
Date: Wed, 16 Apr 2025 14:27:36 +0200
From: Andrew Lunn <andrew@...n.ch>
To: Fiona Klute <fiona.klute@....de>
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 v2] net: phy: microchip: force IRQ polling mode for
 lan88xx

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@lunn.ch
> Fixes: 792aec47d59d ("add microchip LAN88xx phy driver")
> Signed-off-by: Fiona Klute <fiona.klute@....de>
> Cc: kernel-list@...pberrypi.com
> Cc: stable@...r.kernel.org

Reviewed-by: Andrew Lunn <andrew@...n.ch>

    Andrew