netdev - Re: [PATCH net v2] net: ethernet: xscale: Check for PTP support properly

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Message-ID: <168768b8-f26f-4f4d-9b76-230a76c312d2@lunn.ch>
Date: Wed, 11 Feb 2026 16:43:16 +0100
From: Andrew Lunn <andrew@...n.ch>
To: Linus Walleij <linusw@...nel.org>
Cc: Andrew Lunn <andrew+netdev@...n.ch>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
	Richard Cochran <richardcochran@...il.com>,
	Vadim Fedorenko <vadim.fedorenko@...ux.dev>,
	Vladimir Oltean <vladimir.oltean@....com>, netdev@...r.kernel.org
Subject: Re: [PATCH net v2] net: ethernet: xscale: Check for PTP support
 properly

On Wed, Feb 11, 2026 at 01:58:21PM +0100, Linus Walleij wrote:
> In ixp4xx_get_ts_info() ixp46x_ptp_find() is called
> unconditionally despite this feature only existing on
> ixp46x, leading to the following splat from tcpdump:
> 
> root@...nWrt:~# tcpdump -vv -X -i eth0
> (...)
> Unable to handle kernel NULL pointer dereference at virtual address
>   00000238 when read
> (...)
> Call trace:
>  ptp_clock_index from ixp46x_ptp_find+0x1c/0x38
>  ixp46x_ptp_find from ixp4xx_get_ts_info+0x4c/0x64
>  ixp4xx_get_ts_info from __ethtool_get_ts_info+0x90/0x108
>  __ethtool_get_ts_info from __dev_ethtool+0xa00/0x2648
>  __dev_ethtool from dev_ethtool+0x160/0x234
>  dev_ethtool from dev_ioctl+0x2cc/0x460
>  dev_ioctl from sock_ioctl+0x1ec/0x524
>  sock_ioctl from sys_ioctl+0x51c/0xa94
>  sys_ioctl from ret_fast_syscall+0x0/0x44
>  (...)
> Segmentation fault
> 
> Check for ixp46x in ixp46x_ptp_find() before trying to set up
> PTP to avoid this.

>  	ret = ixp46x_ptp_find(&port->timesync_regs, &port->phc_index);
>  	if (ret)
> -		return ret;
> +		return -EOPNOTSUPP;

Changing the error code is unusual. Maybe add to the commit message
why this is needed, or somebody might ask :-)

    Andrew