linux-kernel - Re: [PATCH] x86/calgary: fix bitcast type warnings

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Message-ID: <CAG48ez01TR7xBRgdAyvoHBjttn-ffr-8KBS8sJ904TDm4FLH+Q@mail.gmail.com>
Date:   Fri, 29 Mar 2019 22:45:21 +0100
From:   Jann Horn <jannh@...gle.com>
To:     Mukesh Ojha <mojha@...eaurora.org>
Cc:     Muli Ben-Yehuda <mulix@...ix.org>, Jon Mason <jdmason@...zu.us>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>,
        "the arch/x86 maintainers" <x86@...nel.org>,
        iommu@...ts.linux-foundation.org,
        kernel list <linux-kernel@...r.kernel.org>,
        Logan Gunthorpe <logang@...tatee.com>
Subject: Re: [PATCH] x86/calgary: fix bitcast type warnings

On Fri, Mar 29, 2019 at 9:19 AM Mukesh Ojha <mojha@...eaurora.org> wrote:
> On 3/29/2019 4:29 AM, Jann Horn wrote:
> > The sparse checker attempts to ensure that all conversions between
> > fixed-endianness numbers and numbers with native endianness are explicit.
> > However, the calgary code reads and writes big-endian numbers from/to IO
> > memory using {read,write}{l,q}(), which return native-endian numbers.
> >
> > This could be addressed by putting __force casts all over the place, but
> > that would kind of defeat the point of the warning. Instead, create new
> > helpers {read,write}{l,q}_be() for big-endian IO that convert from/to
> > native endianness.
> >
> > Most of this patch is a straightforward conversion; the following parts
> > aren't just mechanical replacement:
> >
> >   - ->tar_val is now a native-endian number instead of big-endian
> >   - calioc2_handle_quirks() did `cpu_to_be32(readl(target))` when it
> >     intended to do `be32_to_cpu(readl(target))` (but that has no actual
> >     effects outside of type warnings)
> >
> > This gets rid of 108 lines of sparse warnings.
> >
> > Signed-off-by: Jann Horn <jannh@...gle.com>
> > ---
> > compile-tested only
> >
> >   arch/x86/kernel/pci-calgary_64.c | 108 ++++++++++++++++++-------------
> >   1 file changed, 64 insertions(+), 44 deletions(-)
> >
> > diff --git a/arch/x86/kernel/pci-calgary_64.c b/arch/x86/kernel/pci-calgary_64.c
> > index c70720f61a34..36cd66d940fb 100644
> > --- a/arch/x86/kernel/pci-calgary_64.c
> > +++ b/arch/x86/kernel/pci-calgary_64.c
> > @@ -534,6 +534,26 @@ static inline int is_cal_pci_dev(unsigned short device)
> >       return (is_calgary(device) || is_calioc2(device));
> >   }
>
>
> Can the existing api's not be used here like iowrite64be/ioread64be/ or
> similar variant in "include/asm-generic/io.h"

Given what Logan said, I think it probably makes sense to keep the patch as-is?