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List:       linux-pci
Subject:    Re: [PATCH] PCI: rcar: Check for OF device match early
From:       Geert Uytterhoeven <geert () linux-m68k ! org>
Date:       2017-01-31 21:43:39
Message-ID: CAMuHMdUKVsxAHtLBC70EOY5uTcSkMm1qLBUf6mLck6YA=1qaBg () mail ! gmail ! com
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Hi Bjorn,

On Tue, Jan 31, 2017 at 7:09 PM, Bjorn Helgaas <helgaas@kernel.org> wrote:
> On Tue, Jan 31, 2017 at 04:33:15PM +0100, Geert Uytterhoeven wrote:
>> On Tue, Jan 31, 2017 at 4:10 PM, Bjorn Helgaas <bhelgaas@google.com> wrote:
>> > A match in the rcar_pcie_of_match[] table is required, so check that first,
>> > before we start setting up things that need to be undone if it fails.  No
>> > functional change intended.
>> >
>> > Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
>> > ---
>> >  drivers/pci/host/pcie-rcar.c |   10 +++++-----
>> >  1 file changed, 5 insertions(+), 5 deletions(-)
>> >
>> > diff --git a/drivers/pci/host/pcie-rcar.c b/drivers/pci/host/pcie-rcar.c
>> > index 0d9b96c3c49d..c91ff0b91be8 100644
>> > --- a/drivers/pci/host/pcie-rcar.c
>> > +++ b/drivers/pci/host/pcie-rcar.c
>> > @@ -1129,6 +1129,10 @@ static int rcar_pcie_probe(struct platform_device *pdev)
>> >         int err;
>> >         int (*hw_init_fn)(struct rcar_pcie *);
>> >
>> > +       of_id = of_match_device(rcar_pcie_of_match, dev);
>> > +       if (!of_id || !of_id->data)
>> > +               return -EINVAL;
>> > +
>>
>> As this driver is DT-only, none of the above can fail, and you could just do
>>
>>        hw_init_fn = of_device_get_match_data(dev);
>>
>> instead, getting rid of of_id completely.
>
> Oh, I really like that, thanks for pointing that out!
>
> I was about to say that I personally would not check of_id->data for NULL,
> because it is only NULL if somebody adds an entry to rcar_pcie_of_match
> without a .data member.  In that case, I'd rather take the NULL pointer
> dereference than return -EINVAL because it's too easy to ignore the
> -EINVAL.
>
> What do you think about the following?

Thanks, looks fine!

> commit 25bd3aa972ee32f04590aa68b2b785dce36b036a
> Author: Bjorn Helgaas <bhelgaas@google.com>
> Date:   Tue Jan 31 08:45:49 2017 -0600
>
>     PCI: rcar: Use of_device_get_match_data() to simplify probe
>
>     This is a DT-only driver, so the only way to call rcar_pcie_probe() is to
>     match an entry in rcar_pcie_of_match[], so of_id cannot be NULL.
>
>     Furthermore, of_id->data can only be NULL if an rcar_pcie_of_match[] entry
>     has a NULL .data member.  That's a driver defect, and we don't want to
>     return -EINVAL, which is easy to ignore.  We'd rather take the NULL pointer
>     dereference so we notice the problem and fix it.
>
>     Use of_device_get_match_data() to retrieve the hw_init_fn pointer.  No
>     functional change intended.
>
>     Suggested-by: Geert Uytterhoeven <geert@linux-m68k.org>
>     Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>

Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-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
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