netdev - RE: [PATCH net-next] net: enetc: use generic interfaces to get phc

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Message-ID:
 <PAXPR04MB8510ABEC85E704D1289A0E098811A@PAXPR04MB8510.eurprd04.prod.outlook.com>
Date: Fri, 19 Sep 2025 08:48:57 +0000
From: Wei Fang <wei.fang@....com>
To: Kory Maincent <kory.maincent@...tlin.com>, Vladimir Oltean
	<vladimir.oltean@....com>
CC: Claudiu Manoil <claudiu.manoil@....com>, Clark Wang
	<xiaoning.wang@....com>, "Y.B. Lu" <yangbo.lu@....com>,
	"richardcochran@...il.com" <richardcochran@...il.com>,
	"andrew+netdev@...n.ch" <andrew+netdev@...n.ch>, "davem@...emloft.net"
	<davem@...emloft.net>, "edumazet@...gle.com" <edumazet@...gle.com>,
	"kuba@...nel.org" <kuba@...nel.org>, "pabeni@...hat.com" <pabeni@...hat.com>,
	Frank Li <frank.li@....com>, "imx@...ts.linux.dev" <imx@...ts.linux.dev>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH net-next] net: enetc: use generic interfaces to get
 phc_index for ENETC v1

> > It looks like we have a problem and can't call pci_get_slot(), which
> > sleeps on down_read(&pci_bus_sem), from ethtool_ops :: get_ts_info(),
> > which can't sleep, as of commit 4c61d809cf60 ("net: ethtool: Fix
> > suspicious rcu_dereference usage").
> >
> > Köry, do you have any comments or suggestions? Patch is here:
> >
> https://lore.kern/
> el.org%2Fnetdev%2F20250918074454.1742328-1-wei.fang%40nxp.com%2F&d
> ata=05%7C02%7Cwei.fang%40nxp.com%7Cca70608eb6c9487d98e108ddf7571
> de6%7C686ea1d3bc2b4c6fa92cd99c5c301635%7C0%7C0%7C63893867571474
> 2481%7CUnknown%7CTWFpbGZsb3d8eyJFbXB0eU1hcGkiOnRydWUsIlYiOiIwLjA
> uMDAwMCIsIlAiOiJXaW4zMiIsIkFOIjoiTWFpbCIsIldUIjoyfQ%3D%3D%7C0%7C%7
> C%7C&sdata=h6rMPPxArsYdoPOz95UZRU88Oz9IJ3sD6lRjqC5SHMU%3D&reser
> ved=0
>
> This is annoying indeed. I don't know how this enetc drivers works but why
> ts_info needs this pci_get_slot() call? It seems this call seems to not be
> used in ndo_hwtstamp_get/set while ts_info which does not need any hardware
> communication report only a list of capabilities.
>

The ENETC (MAC controller) and the PTP timer are separate devices, they
are both PCIe devices, the PTP timer provides the PHC for ENETC to use, so
enetc_get_ts_info() needs to get the phc_index of the PTP timer, so
pci_get_slot() is called to get the pci_dev pointer of the PTP timer. I can use
pci_get_domain_bus_and_slot() to instead to fix this issue.

I do not know whether it is a good idea to place the get_ts_info() callback
within an atomic lock context. I also noticed that idpf driver also has the
same potential issue (idpf_get_ts_info()).