Re: [PATCH] xen: workaround missing device_type property in pci/pcie nodes

[Stefano Stabellini <sstabellini@xxxxxxxxxx>]

On Tue, 9 Feb 2021, Bertrand Marquis wrote:
> Hi Stefano,
> 
> > On 8 Feb 2021, at 23:56, Stefano Stabellini <sstabellini@xxxxxxxxxx> wrote:
> > 
> > PCI buses differ from default buses in a few important ways, so it is
> > important to detect them properly. Normally, PCI buses are expected to
> > have the following property:
> > 
> >    device_type = "pci"
> > 
> > In reality, it is not always the case. To handle PCI bus nodes that
> > don't have the device_type property, also consider the node name: if the
> > node name is "pcie" or "pci" then consider the bus as a PCI bus.
> > 
> > This commit is based on the Linux kernel commit
> > d1ac0002dd29 "of: address: Work around missing device_type property in
> > pcie nodes".
> > 
> > This fixes Xen boot on RPi4.
> 
> We are really handling here a wrong device-tree bug that could easily be fixed
> by the user.
> We should at least mention in the commit message that this is a workaround
> to solve RPi4 buggy device tree.

Not sure if it can be "easily" fixed by the user -- it took me a few
hours to figure out what the problem was, and I know Xen and device tree
pretty well :-)

Yes it would be good to have a link to the discussion in the commit
message, using the Link tag. It could be done on commit, or I can add it
to the next version.

Link: https://lore.kernel.org/xen-devel/YBmQQ3Tzu++AadKx@xxxxxxxxxxxxxxxx/


> > 
> > Signed-off-by: Stefano Stabellini <stefano.stabellini@xxxxxxxxxx>
> > 
> > diff --git a/xen/common/device_tree.c b/xen/common/device_tree.c
> > index 18825e333e..f1a96a3b90 100644
> > --- a/xen/common/device_tree.c
> > +++ b/xen/common/device_tree.c
> > @@ -563,14 +563,28 @@ static unsigned int dt_bus_default_get_flags(const 
> > __be32 *addr)
> >  * PCI bus specific translator
> >  */
> > 
> > +static bool_t dt_node_is_pci(const struct dt_device_node *np)
> > +{
> > +    bool is_pci = !strcmp(np->name, "pcie") || !strcmp(np->name, "pci");
> 
> The Linux commit is a bit more restrictive and only does that for “pcie”.
> Any reason why you also want to have this workaround done also for “pci” ?

Yes, that's because in our case the offending node is named "pci" not
"pcie" so the original Linux commit wouldn't cover it.


> > +
> > +    if (is_pci)
> > +        printk(XENLOG_WARNING "%s: Missing device_type\n", np->full_name);
> > +
> > +    return is_pci;
> > +}
> > +
> > static bool_t dt_bus_pci_match(const struct dt_device_node *np)
> > {
> >     /*
> >      * "pciex" is PCI Express "vci" is for the /chaos bridge on 1st-gen PCI
> >      * powermacs "ht" is hypertransport
> > +     *
> > +     * If none of the device_type match, and that the node name is
> > +     * "pcie" or "pci", accept the device as PCI (with a warning).
> >      */
> >     return !strcmp(np->type, "pci") || !strcmp(np->type, "pciex") ||
> > -        !strcmp(np->type, "vci") || !strcmp(np->type, "ht");
> > +        !strcmp(np->type, "vci") || !strcmp(np->type, "ht") ||
> > +        dt_node_is_pci(np);
> > }
> > 
> > static void dt_bus_pci_count_cells(const struct dt_device_node *np,
> > 
> 
>