netdev - Re: [RFC net-next v1 2/2] net. phy: dp83tg720: Add randomized polling intervals for unstable link detection

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Message-ID: <Z0gksn9nEKJOY5Ul@pengutronix.de>
Date: Thu, 28 Nov 2024 09:07:14 +0100
From: Oleksij Rempel <o.rempel@...gutronix.de>
To: Andrew Lunn <andrew@...n.ch>
Cc: Heiner Kallweit <hkallweit1@...il.com>,
	Russell King <linux@...linux.org.uk>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
	kernel@...gutronix.de, linux-kernel@...r.kernel.org,
	netdev@...r.kernel.org
Subject: Re: [RFC net-next v1 2/2] net. phy: dp83tg720: Add randomized
 polling intervals for unstable link detection

Hi Andrew,

On Wed, Nov 27, 2024 at 04:37:49PM +0100, Andrew Lunn wrote:
> On Wed, Nov 27, 2024 at 02:10:11PM +0100, Oleksij Rempel wrote:
> > Address the limitations of the DP83TG720 PHY, which cannot reliably detect or
> > report a stable link state. To handle this, the PHY must be periodically reset
> > when the link is down. However, synchronized reset intervals between the PHY
> > and its link partner can result in a deadlock, preventing the link from
> > re-establishing.
> > 
> > This change introduces a randomized polling interval when the link is down to
> > desynchronize resets between link partners.
> 
> Hi Oleksij
> 
> What other solutions did you try? I'm wondering if this is more
> complex than it needs to be. Could you add a random delay in
> dp83tg720_read_status() when it decides to do a reset?

Yes, this would be possible, but there are multiple reasons I decided to
go this way:
- in link down case, it is better to increase polling frequency, it
  allows to reduce link up time.
- there are PHYs, for example an integrated to LAN9372 which supports
  only link down interrupt. As long as link is down, it should be
  polled.
- i'm working on generic PHY stats support and PHYs need to be polled,
  even with IRQ support, just less frequently.

I can add it to the commit message.

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