netdev - Re: [net-next] net: phy: Check for read errors in SIOCGMIIREG

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Message-ID: <49f85a5f-3393-4d7b-8fcb-5eec00e564d6@lunn.ch>
Date: Tue, 3 Sep 2024 20:41:06 +0200
From: Andrew Lunn <andrew@...n.ch>
To: Niklas Söderlund <niklas.soderlund+renesas@...natech.se>
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>,
	netdev@...r.kernel.org, linux-renesas-soc@...r.kernel.org
Subject: Re: [net-next] net: phy: Check for read errors in SIOCGMIIREG

On Tue, Sep 03, 2024 at 07:15:36PM +0200, Niklas Söderlund wrote:
> When reading registers from the PHY using the SIOCGMIIREG IOCTL any
> errors returned from either mdiobus_read() or mdiobus_c45_read() are
> ignored, and parts of the returned error is passed as the register value
> back to user-space.
> 
> For example, if mdiobus_c45_read() is used with a bus that do not
> implement the read_c45() callback -EOPNOTSUPP is returned. This is
> however directly stored in mii_data->val_out and returned as the
> registers content. As val_out is a u16 the error code is truncated and
> returned as a plausible register value.
> 
> Fix this by first checking the return value for errors before returning
> it as the register content.
> 
> Before this patch,
> 
>     # phytool read eth0/0:1/0
>     0xffa1
> 
> After this change,
> 
>     $ phytool read eth0/0:1/0
>     error: phy_read (-95)
> 
> Signed-off-by: Niklas Söderlund <niklas.soderlund+renesas@...natech.se>

write is similarly broken, but i don't think we care about that.

Thanks

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

    Andrew