Re: [PATCH v1] asm-generic: introduce be56 unaligned accessors

[Marius.Cristea]

Hi David,

  Thank you very much for the feedback.

On Sun, 2024-09-29 at 21:16 +0000, David Laight wrote:
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> From: marius.cristea@xxxxxxxxxxxxx
> > Sent: 27 September 2024 09:36
> > 
> > The PAC194X, IIO driver, is using some unaligned 56 bit registers.
> > Provide some helper accessors in preparation for the new driver.
> 
> Someone please shoot the hardware engineer ;-)
> 
> Do separate unaligned access of the first 4 bytes and last four
> bytes.
> It can't matter if the middle byte is accessed twice.
> 
> Or, for reads read 8 bytes from 'p & ~1ul' and then fixup
> the value.
> 

Do you recommend me to drop this patch?

I know that there are some "workarounds", but those didn't "looks"
nice. I was using that function locally and I got a suggestion from the
IIO subsystem maintainer to move it into the kernel in order for others
to used it.


Thanks,
Marius



>         David
> 
> > 
> > Signed-off-by: Marius Cristea <marius.cristea@xxxxxxxxxxxxx>
> > ---
> >  include/asm-generic/unaligned.h | 27 +++++++++++++++++++++++++++
> >  1 file changed, 27 insertions(+)
> > 
> > diff --git a/include/asm-generic/unaligned.h b/include/asm-
> > generic/unaligned.h
> > index a84c64e5f11e..d171a9f2377a 100644
> > --- a/include/asm-generic/unaligned.h
> > +++ b/include/asm-generic/unaligned.h
> > @@ -152,4 +152,31 @@ static inline u64 get_unaligned_be48(const
> > void *p)
> >       return __get_unaligned_be48(p);
> >  }
> > 
> > +static inline void __put_unaligned_be56(const u64 val, u8 *p)
> > +{
> > +     *p++ = (val >> 48) & 0xff;
> > +     *p++ = (val >> 40) & 0xff;
> > +     *p++ = (val >> 32) & 0xff;
> > +     *p++ = (val >> 24) & 0xff;
> > +     *p++ = (val >> 16) & 0xff;
> > +     *p++ = (val >> 8) & 0xff;
> > +     *p++ = val & 0xff;
> > +}
> > +
> > +static inline void put_unaligned_be56(const u64 val, void *p)
> > +{
> > +     __put_unaligned_be56(val, p);
> > +}
> > +
> > +static inline u64 __get_unaligned_be56(const u8 *p)
> > +{
> > +     return (u64)p[0] << 48 | (u64)p[1] << 40 | (u64)p[2] << 32 |
> > +             (u64)p[3] << 24 | p[4] << 16 | p[5] << 8 | p[6];
> > +}
> > +
> > +static inline u64 get_unaligned_be56(const void *p)
> > +{
> > +     return __get_unaligned_be56(p);
> > +}
> > +
> >  #endif /* __ASM_GENERIC_UNALIGNED_H */
> > 
> > base-commit: b82c1d235a30622177ce10dcb94dfd691a49922f
> > --
> > 2.43.0
> > 
> 
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