linux-kernel - Re: net: stmmac: dwmac-imx: half duplex crash

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Date:   Tue, 26 Apr 2022 15:36:55 +0200
From:   Andrew Lunn <andrew@...n.ch>
To:     Marcel Ziswiler <marcel.ziswiler@...adex.com>
Cc:     "linux-imx@....com" <linux-imx@....com>,
        "peppe.cavallaro@...com" <peppe.cavallaro@...com>,
        "linux-stm32@...md-mailman.stormreply.com" 
        <linux-stm32@...md-mailman.stormreply.com>,
        "davem@...emloft.net" <davem@...emloft.net>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "pabeni@...hat.com" <pabeni@...hat.com>,
        "shawnguo@...nel.org" <shawnguo@...nel.org>,
        "joabreu@...opsys.com" <joabreu@...opsys.com>,
        "kernel@...gutronix.de" <kernel@...gutronix.de>,
        "s.hauer@...gutronix.de" <s.hauer@...gutronix.de>,
        "kuba@...nel.org" <kuba@...nel.org>,
        "alexandre.torgue@...s.st.com" <alexandre.torgue@...s.st.com>,
        "mcoquelin.stm32@...il.com" <mcoquelin.stm32@...il.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "festevam@...il.com" <festevam@...il.com>
Subject: Re: net: stmmac: dwmac-imx: half duplex crash

> > Anyway, this is roughly there the check should go.
> 
> You mean it would need an additional check against advertising nothing?

I would check for a mode being requested which is not
supported. phydev->supported tells you what the MAC/PHY can actually
do. If there is a bit set which is not a member of that, return
EINVAL. I don't think the plumbing is there, but netlink ethtool
allows you to also return a text message via extack, so you could give
the user a bit more information, the link mode which is invalid.

> Well, we are gearing up on our automated testing infrastructure and asking my humble opinion on what exactly to
> test concerning the Ethernet subsystem I gave the brilliant suggestion to try each and every supported link
> mode (;-p). Which actually works just fine on every other hardware of ours just not the i.MX 8M Plus with the
> DWMAC IP (remember, even FEC MAC works). So for now this is not something a customer of ours has real trouble
> with but it raised some questions concerning whether or not and what exactly we do support...

So in practice, this should not happen. You don't advertise the half
modes, so you should never end up in a half mode. So it is not a
problem :-)

	Andrew