linux-kernel - Re: [PATCH] net: usb: lan78xx: Fix lost EEPROM read timeout error(-ETIMEDOUT) in lan78xx_read_raw

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Message-ID: <aNzojoXK-m1Tn6Lc@pengutronix.de>
Date: Wed, 1 Oct 2025 10:38:38 +0200
From: Oleksij Rempel <o.rempel@...gutronix.de>
To: Bhanu Seshu Kumar Valluri <bhanuseshukumar@...il.com>
Cc: Jakub Kicinski <kuba@...nel.org>, Thangaraj.S@...rochip.com,
	Rengarajan.S@...rochip.com, UNGLinuxDriver@...rochip.com,
	andrew+netdev@...n.ch, davem@...emloft.net, edumazet@...gle.com,
	pabeni@...hat.com, netdev@...r.kernel.org,
	linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org,
	syzbot+62ec8226f01cb4ca19d9@...kaller.appspotmail.com
Subject: Re: [PATCH] net: usb: lan78xx: Fix lost EEPROM read timeout
 error(-ETIMEDOUT) in lan78xx_read_raw_eeprom

On Wed, Oct 01, 2025 at 02:01:24PM +0530, Bhanu Seshu Kumar Valluri wrote:
> On 01/10/25 13:54, Oleksij Rempel wrote:
> > On Wed, Oct 01, 2025 at 01:40:56PM +0530, Bhanu Seshu Kumar Valluri wrote:
> >> On 01/10/25 13:12, Oleksij Rempel wrote:
> >>> Hi,
> >>>
> >>> On Wed, Oct 01, 2025 at 10:07:21AM +0530, Bhanu Seshu Kumar Valluri wrote:
> >>>> On 01/10/25 06:09, Jakub Kicinski wrote:
> >>>>> On Tue, 30 Sep 2025 14:19:02 +0530 Bhanu Seshu Kumar Valluri wrote:
> >>>>>> +	if (dev->chipid == ID_REV_CHIP_ID_7800_) {
> >>>>>> +		int rc = lan78xx_write_reg(dev, HW_CFG, saved);
> >>>>>> +		/* If USB fails, there is nothing to do */
> >>>>>> +		if (rc < 0)
> >>>>>> +			return rc;
> >>>>>> +	}
> >>>>>> +	return ret;
> >>>>>
> >>>>> I don't think you need to add and handle rc here separately?
> >>>>> rc can only be <= so save the answer to ret and "fall thru"?
> >>>>
> >>>> The fall thru path might have been reached with ret holding EEPROM read timeout
> >>>> error status. So if ret is used instead of rc it might over write the ret with 0 when 
> >>>> lan78xx_write_reg returns success and timeout error status would be lost.
> >>>
> >>> Ack, I see. It may happen if communication with EEPROM will fail. The same
> >>> would happen on write path too. Is it happened with real HW or it is
> >>> some USB emulation test? For me it is interesting why EEPROM is timed
> >>> out.
> >>
> >> The sysbot's log with message "EEPROM read operation timeout" confirms that EEPROM read
> >> timeout occurring. I tested the same condition on EVB-LAN7800LC by simulating 
> >> timeout during probe.
> > 
> > Do you simulating timeout during probe by modifying the code, or it is
> > real HW issue?
> > 
> 
> On my real hardware timeout didn't occur. So I simulated it once by modifying the code
> to confirm the BUG. The BUG has occurred confirming syzbot finding.

Ok, thank you!

Can you please add similar change to lan78xx_write_raw_eeprom. syzbot
will find it soon or later.

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