RE: [PATCH net-next] net: enetc: use generic interfaces to get phc_index for ENETC v1

[Wei Fang]

> > 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
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> 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()).