linux-kernel - Re: [PATCH v1] iommu/ipmmu-vmsa: Don't register as BUS IOMMU if machine doesn't have IPMMU-VMSA

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Date:   Mon, 27 Aug 2018 16:20:26 +0200
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     Laurent Pinchart <laurent.pinchart@...asonboard.com>
Cc:     digetx@...il.com, Joerg Roedel <joro@...tes.org>,
        Laurent Pinchart <laurent.pinchart+renesas@...asonboard.com>,
        Marc Dietrich <marvin24@....de>,
        Linux IOMMU <iommu@...ts.linux-foundation.org>,
        linux-tegra@...r.kernel.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Magnus Damm <magnus.damm@...il.com>
Subject: Re: [PATCH v1] iommu/ipmmu-vmsa: Don't register as BUS IOMMU if
 machine doesn't have IPMMU-VMSA

Hi Laurent,

On Fri, Jul 27, 2018 at 11:09 AM Laurent Pinchart
<laurent.pinchart@...asonboard.com> wrote:
> (CC'ing Geert and Magnus)
>
> Thank you for the patch.
>
> On Friday, 27 July 2018 00:19:16 EEST Dmitry Osipenko wrote:
> > This fixes kernel crashing on NVIDIA Tegra if kernel is compiled in
> > a multiplatform configuration and IPMMU-VMSA driver is enabled.
> >
> > Cc: <stable@...r.kernel.org> # v3.20+
> > Signed-off-by: Dmitry Osipenko <digetx@...il.com>
> > ---
> >  drivers/iommu/ipmmu-vmsa.c | 7 +++++++
> >  1 file changed, 7 insertions(+)
> >
> > diff --git a/drivers/iommu/ipmmu-vmsa.c b/drivers/iommu/ipmmu-vmsa.c
> > index 9e8495762bc8..78c50db9cd71 100644
> > --- a/drivers/iommu/ipmmu-vmsa.c
> > +++ b/drivers/iommu/ipmmu-vmsa.c
> > @@ -1109,12 +1109,19 @@ static struct platform_driver ipmmu_driver = {
> >
> >  static int __init ipmmu_init(void)
> >  {
> > +     struct device_node *np;
> >       static bool setup_done;
> >       int ret;
> >
> >       if (setup_done)
> >               return 0;
> >
> > +     np = of_find_matching_node(NULL, ipmmu_of_ids);
> > +     if (!np)
> > +             return 0;
> > +
> > +     of_node_put(np);
> > +
>
> While functionally correct, this will add some unnecessary overhead when
> iommu_init() is called from IOMMU_OF_DECLARE(). I'm OK with this fix as a
> temporary measure to solve your problem, but we need to address the underlying
> issue properly.
>
> Geert, Magnus, the ipmmu-vmsa driver is a bit of a mess. We should brush it up
> and start using IOMMU_OF_DECLARE() on all platforms (and eventually get rid of
> bus_set_iommu() completely...). Do you have plans to address this ? If not,
> could you please add it to your to-do list ?

On the contrary: IOMMU_OF_DECLARE() has been removed.

>
> >       ret = platform_driver_register(&ipmmu_driver);
> >       if (ret < 0)
> >               return ret;

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds