linux-kernel - Re: [PATCH] net: phy: adin1100: Fix nullptr exception for phy interrupts

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Date: Thu, 18 Jan 2024 18:36:16 +0100
From: Heiner Kallweit <hkallweit1@...il.com>
To: Andrew Lunn <andrew@...n.ch>,
 Andre Werner <andre.werner@...tec-electronic.com>
Cc: davem@...emloft.net, edumazet@...gle.com, kuba@...nel.org,
 pabeni@...hat.com, linux@...linux.org.uk, netdev@...r.kernel.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH] net: phy: adin1100: Fix nullptr exception for phy
 interrupts

On 18.01.2024 17:53, Andrew Lunn wrote:
> On Thu, Jan 18, 2024 at 11:43:41AM +0100, Andre Werner wrote:
>> If using ADIN1100 as an external phy, e.g. in combination with
>> "smsc95xx", we ran into nullptr exception by creating a link.
>>
>> In our case the "smsc95xx" does not check for an available interrupt handler
>> on external phy driver to use poll instead of interrupts if no handler is
>> available. So we decide to implement a small handler in the phy driver
>> to support other MACs as well.
>>
>> I update the driver to add an interrupt handler because libphy
>> does not check if their is a interrupt handler available either.
>>
>> There are several interrupts maskable at the phy, but only link change interrupts
>> are handled by the driver yet.
>>
>> We tested the combination "smsc95xx" and "adin1100" with Linux Kernel 6.6.9
>> and Linux Kernel 6.1.0, respectively.
> 
> Hi Andre
> 
> A few different things....
> 
> Please could you give more details of the null pointer
> exception. phylib should test if the needed methods have been
> implemented in the PHY driver, and not tried to use interrupts when
> they are missing. It should of polled the PHY. So i would like to
> understand what went wrong. Maybe we have a phylib core bug we should
> be fixing. Or a bug in the smsc95xx driver.
> 
Seems to be a bug in smsc95xx. The following is the relevant code piece.

ret = mdiobus_register(pdata->mdiobus);
	if (ret) {
		netdev_err(dev->net, "Could not register MDIO bus\n");
		goto free_mdio;
	}

	pdata->phydev = phy_find_first(pdata->mdiobus);
	if (!pdata->phydev) {
		netdev_err(dev->net, "no PHY found\n");
		ret = -ENODEV;
		goto unregister_mdio;
	}

	pdata->phydev->irq = phy_irq;

The interrupt is set too late, after phy_probe(), where we have this:

if (!phy_drv_supports_irq(phydrv) && phy_interrupt_is_valid(phydev))
		phydev->irq = PHY_POLL;

So we would have two steps:
1. Fix the smsc95xx bug (as the same issue could occur with another PHY type)
2. Add interrupt support to adin1100 as an improvement

> Please take a read of
> https://www.kernel.org/doc/html/latest/process/maintainer-netdev.html
> 
> Patches like this should be against net-next, not 6.6.9 etc. Also,
> net-next is currently closed due to the merge window being open. Its
> fine to post patches, but please mark them RFC until the merge window
> is over.
> 
> The patch itself looks O.K, but i would make the commit message more
> formal. You can add additional comments under the --- which will not
> become part of the git history.
> 
>        Andrew