netdev - Re: [PATCH] net: dp83822: disable false carrier interrupt

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Date:   Fri, 17 Jun 2022 19:55:54 +0200
From:   Andrew Lunn <andrew@...n.ch>
To:     Enguerrand de Ribaucourt 
        <enguerrand.de-ribaucourt@...oirfairelinux.com>
Cc:     davem@...emloft.net, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux@...linux.org.uk,
        hkallweit1@...il.com
Subject: Re: [PATCH] net: dp83822: disable false carrier interrupt

On Fri, Jun 17, 2022 at 03:46:11PM +0200, Enguerrand de Ribaucourt wrote:
> When unplugging an Ethernet cable, false carrier events were produced by
> the PHY at a very high rate. Once the false carrier counter full, an
> interrupt was triggered every few clock cycles until the cable was
> replugged. This resulted in approximately 10k/s interrupts.
> 
> Since the false carrier counter (FCSCR) is never used, we can safely
> disable this interrupt.
> 
> In addition to improving performance, this also solved MDIO read
> timeouts I was randomly encountering with an i.MX8 fec MAC because of
> the interrupt flood. The interrupt count and MDIO timeout fix were
> tested on a v5.4.110 kernel.
> 
> Signed-off-by: Enguerrand de Ribaucourt <enguerrand.de-ribaucourt@...oirfairelinux.com>
> ---
>  drivers/net/phy/dp83822.c | 1 -
>  1 file changed, 1 deletion(-)
> 
> diff --git a/drivers/net/phy/dp83822.c b/drivers/net/phy/dp83822.c
> index e6ad3a494d32..95ef507053a6 100644
> --- a/drivers/net/phy/dp83822.c
> +++ b/drivers/net/phy/dp83822.c
> @@ -230,7 +230,6 @@ static int dp83822_config_intr(struct phy_device *phydev)
>  			return misr_status;
>  
>  		misr_status |= (DP83822_RX_ERR_HF_INT_EN |
> -				DP83822_FALSE_CARRIER_HF_INT_EN |

Does the same problem exist for RX_ERR_HF_INT ? That appears to be
that the RX error counter has reached half full. I don't see anything
using register 0x15.

      Andrew