On Wed, 2020-04-15 at 11:30 -0700, Saravana Kannan wrote:
> On Wed, Apr 15, 2020 at 8:06 AM Nicolas Saenz Julienne
> <nsaenzjulienne@xxxxxxx> wrote:
> > When creating a consumer/supplier relationship between two devices, make
> > sure the supplier node is actually active. Otherwise this will create a
> > device link that will never be fulfilled. This, in the worst case
> > scenario, will hang the system during boot.
> >
> > Note that, in practice, the fact that a device-tree represented
> > consumer/supplier relationship isn't fulfilled will not prevent devices
> > from successfully probing.
> >
> > Fixes: a3e1d1a7f5fc ("of: property: Add functional dependency link from DT
> > bindings")
> > Signed-off-by: Nicolas Saenz Julienne <nsaenzjulienne@xxxxxxx>
> > ---
> > drivers/of/property.c | 7 +++++++
> > 1 file changed, 7 insertions(+)
> >
> > diff --git a/drivers/of/property.c b/drivers/of/property.c
> > index a8c2b13521b27..487685ff8bb19 100644
> > --- a/drivers/of/property.c
> > +++ b/drivers/of/property.c
> > @@ -1052,6 +1052,13 @@ static int of_link_to_phandle(struct device *dev,
> > struct device_node *sup_np,
> > return -ENODEV;
> > }
> >
> > + /* Don't allow linking a device node as consumer of a disabled node
> > */
> > + if (!of_device_is_available(sup_np)) {
> > + dev_dbg(dev, "Not linking to %pOFP - Not available\n",
> > sup_np);
> > + of_node_put(sup_np);
> > + return -ENODEV;
> > + }
> > +
>
> Again, surprised I haven't hit this situation with the number of
> disabled devices I have.
I'll point out to the example that triggered this issue on my reply to patch
#4.
> The idea is right, but the implementation can be better. I think this
> check needs to be the first check after the of_node_get(sup_np) --
> before we do any of the "walk up to find the device" part.
>
> Otherwise, you could have a supplier device (the one with compatible
> prop) that's available with a child node that's disabled. And the
> phandle could be pointing to that disabled child node. If you don't do
> this as the first check, you might still try to form a pointless
> device link. It won't affect probing (because the actual struct device
> will probe) but it's still a pointless device link and a pointless
> delay in probing, etc.
Agree, I'll update the patch.
Regards,
Nicolas
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