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

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Message-ID: <86a5k8nbh1.wl-maz@kernel.org>
Date: Wed, 29 May 2024 11:44:58 +0100
From: Marc Zyngier <maz@...nel.org>
To: Anup Patel <apatel@...tanamicro.com>
Cc: devicetree@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org,
	linux-riscv@...ts.infradead.org,
	Saravana Kannan <saravanak@...gle.com>,
	Rob Herring <robh@...nel.org>
Subject: Re: [PATCH] of: property: Fix fw_devlink handling of interrupt-map

On Wed, 29 May 2024 11:16:30 +0100,
Anup Patel <apatel@...tanamicro.com> wrote:
> 
> On Wed, May 29, 2024 at 12:03 PM Marc Zyngier <maz@...nel.org> wrote:
> >
> > On Wed, 29 May 2024 06:15:52 +0100,
> > Anup Patel <apatel@...tanamicro.com> wrote:
> > >
> > > On Tue, May 28, 2024 at 10:11 PM Marc Zyngier <maz@...nel.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@...nel.org>
> > > > Cc: Anup Patel <apatel@...tanamicro.com>
> > > > Cc: Saravana Kannan <saravanak@...gle.com>
> > > > Cc: Rob Herring (Arm) <robh@...nel.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.
> 
> If we change of_irq_parse_raw() to use of_bus_n_addr_cells()
> then it would still break for RISC-V.

I'm not trying to "fix" riscv. I'm merely outlining that you are
relying on both broken DTs and a buggy OS.

> 
> Using of_bus_n_addr_cells() over here forces interrupt controller
> DT nodes to have a "#address-cells" DT property. There are many
> interrupt controller (e.g. RISC-V PLIC or RISC-V APLIC) where the
> DT bindings don't require "#address-cells" DT property and existing
> DTS files with such interrupt controllers don't have it either.

It forces you to set #address-cells *if you rely on a different
value in a child node*. It's not like the semantics are new.

> 
> In the RISC-V world, there have been quite a few QEMU releases
> where the generated DT node of the interrupt controller does not
> have the "#address-cells" property. This patch breaks the kernel
> for all such QEMU releases.

Congratulations, you've forked DT. News at 11.

> 
> I think we should align the implementation in parse_interrupt_map()
> with of_irq_parse_raw() and use of_property_read_u32() instead of
> of_bus_n_addr_cells().

I think we should fix the kernel and quirk riscv as broken, just like
PPC or sparc.

	M.

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