On Thu, Sep 02, 2021 at 01:50:51AM +0300, Vladimir Oltean wrote:
> diff --git a/drivers/net/phy/phy_device.c b/drivers/net/phy/phy_device.c
> index 52310df121de..2c22a32f0a1c 100644
> --- a/drivers/net/phy/phy_device.c
> +++ b/drivers/net/phy/phy_device.c
> @@ -1386,8 +1386,16 @@ int phy_attach_direct(struct net_device *dev, struct phy_device *phydev,
>
> /* Assume that if there is no driver, that it doesn't
> * exist, and we should use the genphy driver.
> + * The exception is during probing, when the PHY driver might have
> + * attempted a probe but has requested deferral. Since there might be
> + * MAC drivers which also attach to the PHY during probe time, try
> + * harder to bind the specific PHY driver, and defer the MAC driver's
> + * probing until then.
> */
> if (!d->driver) {
> + if (device_pending_probe(d))
> + return -EPROBE_DEFER;
Something else that concerns me here.
As noted, many network drivers attempt to attach their PHY when the
device is brought up, and not during their probe function.
Taking a driver at random:
drivers/net/ethernet/renesas/sh_eth.c
sh_eth_phy_init() calls of_phy_connect() or phy_connect(), which
ultimately calls phy_attach_direct() and propagates the error code
via an error pointer.
sh_eth_phy_init() propagates the error code to its caller,
sh_eth_phy_start(). This is called from sh_eth_open(), which
probagates the error code. This is called from .ndo_open... and it's
highly likely -EPROBE_DEFER will end up being returned to userspace
through either netlink or netdev ioctls.
Since EPROBE_DEFER is not an error number that we export to
userspace, this should basically never be exposed to userspace, yet
we have a path that it _could_ be exposed if the above condition
is true.
If device_pending_probe() returns true e.g. during initial boot up
while modules are being loaded - maybe the phy driver doesn't have
all the resources it needs because of some other module that hasn't
finished initialising - then we have a window where this will be
exposed to userspace.
So, do we need to fix all the network drivers to do something if
their .ndo_open method encounters this? If so, what? Sleep a bit
and try again? How many times to retry? Convert the error code into
something else, causing userspace to fail where it worked before? If
so which error code?
I think this needs to be thought through a bit better. In this case,
I feel that throwing -EPROBE_DEFER to solve one problem with one
subsystem can result in new problems elsewhere.
We did have an idea at one point about reserving some flag bits in
phydev->dev_flags for phylib use, but I don't think that happened.
If this is the direction we want to go, I think we need to have a
flag in dev_flags so that callers opt-in to the new behaviour whereas
callers such as from .ndo_open keep the old behaviour - because they
just aren't setup to handle an -EPROBE_DEFER return from these
functions.
--
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