Re: [PATCH] of: property: Fix fw_devlink handling of interrupt-map

[Marc Zyngier <maz@kernel.org>]

On Wed, 29 May 2024 06:15:52 +0100,
Anup Patel <apatel@ventanamicro.com> wrote:
> 
> On Tue, May 28, 2024 at 10:11 PM Marc Zyngier <maz@kernel.org> wrote:
> >
> > Commit d976c6f4b32c ("of: property: Add fw_devlink support for
> > interrupt-map property") tried to do what it says on the tin,
> > but failed on a couple of points:
> >
> > - it confuses bytes and cells. Not a huge deal, except when it
> >   comes to pointer arithmetic
> >
> > - it doesn't really handle anything but interrupt-maps that have
> >   their parent #address-cells set to 0
> >
> > The combinations of the two leads to some serious fun on my M1
> > box, with plenty of WARN-ON() firing all over the shop, and
> > amusing values being generated for interrupt specifiers.
> >
> > Address both issues so that I can boot my machines again.
> >
> > Fixes: d976c6f4b32c ("of: property: Add fw_devlink support for interrupt-map property")
> > Signed-off-by: Marc Zyngier <maz@kernel.org>
> > Cc: Anup Patel <apatel@ventanamicro.com>
> > Cc: Saravana Kannan <saravanak@google.com>
> > Cc: Rob Herring (Arm) <robh@kernel.org>
> 
> Thanks for the fix patch but unfortunately it breaks for RISC-V.
> 
> > ---
> >  drivers/of/property.c | 16 ++++++++++++++--
> >  1 file changed, 14 insertions(+), 2 deletions(-)
> >
> > diff --git a/drivers/of/property.c b/drivers/of/property.c
> > index 1c83e68f805b..9adebc63bea9 100644
> > --- a/drivers/of/property.c
> > +++ b/drivers/of/property.c
> > @@ -1322,7 +1322,13 @@ static struct device_node *parse_interrupt_map(struct device_node *np,
> >         addrcells = of_bus_n_addr_cells(np);
> >
> >         imap = of_get_property(np, "interrupt-map", &imaplen);
> > -       if (!imap || imaplen <= (addrcells + intcells))
> > +       imaplen /= sizeof(*imap);
> > +
> > +       /*
> > +        * Check that we have enough runway for the child unit interrupt
> > +        * specifier and a phandle. That's the bare minimum we can expect.
> > +        */
> > +       if (!imap || imaplen <= (addrcells + intcells + 1))
> >                 return NULL;
> >         imap_end = imap + imaplen;
> >
> > @@ -1346,8 +1352,14 @@ static struct device_node *parse_interrupt_map(struct device_node *np,
> >                 if (!index)
> >                         return sup_args.np;
> >
> > -               of_node_put(sup_args.np);
> > +               /*
> > +                * Account for the full parent unit interrupt specifier
> > +                * (address cells, interrupt cells, and phandle).
> > +                */
> > +               imap += of_bus_n_addr_cells(sup_args.np);
> 
> This breaks for RISC-V because we don't have "#address-cells"
> property in interrupt controller DT node and of_bus_n_addr_cells()
> retrieves "#address-cells" from the parent of interrupt controller.

That's a feature, not a bug. #address-cells, AFAICT, applies to all
child nodes until you set it otherwise.

> 
> The of_irq_parse_raw() looks for "#address-cells" property
> in the interrupt controller DT node only so we should do a
> similar thing here as well.

This looks more like a of_irq_parse_raw() bug than anything else.

> 
> The below change on top of this patch worked for me.
> 
> diff --git a/drivers/of/property.c b/drivers/of/property.c
> index 9adebc63bea9..f54da2989ea9 100644
> --- a/drivers/of/property.c
> +++ b/drivers/of/property.c
> @@ -1308,7 +1308,7 @@ static struct device_node
> *parse_interrupt_map(struct device_node *np,
>  {
>      const __be32 *imap, *imap_end, *addr;
>      struct of_phandle_args sup_args;
> -    u32 addrcells, intcells;
> +    u32 addrcells, intcells, paddrcells;
>      int i, imaplen;
> 
>      if (!IS_ENABLED(CONFIG_OF_IRQ))
> @@ -1356,7 +1356,8 @@ static struct device_node
> *parse_interrupt_map(struct device_node *np,
>           * Account for the full parent unit interrupt specifier
>           * (address cells, interrupt cells, and phandle).
>           */
> -        imap += of_bus_n_addr_cells(sup_args.np);
> +        if (!of_property_read_u32(sup_args.np, "#address-cells", &paddrcells))
> +            imap += paddrcells;

This looks wrong to me for the reason I outlined above: you need to
look for a valid #address-cells all along the parent chain, not just
in the interrupt-controller node.

	M.

-- 
Without deviation from the norm, progress is not possible.