Re: [PATCH] iio:gyro:mpu3050 Treat otp value as a __le64 and use FIELD_GET() to break up

[Jonathan Cameron <jic23@kernel.org>]

On Sun, 29 Nov 2020 02:11:01 +0100
Linus Walleij <linus.walleij@linaro.org> wrote:

> On Sun, Nov 29, 2020 at 12:18 AM Andy Shevchenko
> <andy.shevchenko@gmail.com> wrote:
> > On Sun, Nov 29, 2020 at 12:22 AM Linus Walleij <linus.walleij@linaro.org> wrote:  
> > > On Sat, Nov 28, 2020 at 7:54 PM Jonathan Cameron <jic23@kernel.org> wrote:
> > >  
> > > > From: Jonathan Cameron <Jonathan.Cameron@huawei.com>
> > > >
> > > > Inspired by Andy Shevchenko's proposal to use get_unaligned_leXX().
> > > >
> > > > The whole one time programable memory is treated as a single 64bit
> > > > little endian value.  Thus we can avoid a lot of messy handling
> > > > of fields overlapping byte boundaries by just loading and manipulating
> > > > it as an __le64 converted to a u64.  That lets us just use FIELD_GET()
> > > > and GENMASK() to extract the values desired.
> > > >
> > > > Note only build tested.
> > > >
> > > > Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
> > > > Cc: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
> > > > Cc: Linus Walleij <linus.walleij@linaro.org>  
> > >
> > > Are there any specific prerequisites? linux-next?
> > >
> > > When I apply this and try to compile for an ARMv7 target I get
> > > a lot of noise and an error:
> > >
> > > In file included from <command-line>:0:0:
> > > ../drivers/iio/gyro/mpu3050-core.c: In function ‘mpu3050_hw_init’:
> > > ../include/linux/bits.h:36:11: warning: right shift count is negative
> > > [-Wshift-count-negative]
> > >    (~UL(0) >> (BITS_PER_LONG - 1 - (h))))  
> >
> > I think GENMASK_ULL() has to be used.  
> 
> Oh indeed. It works as long as one just try to test-compile it on a 64bit
> machine of course :D

Doh.  That's me being lazy :(

Will flip them all over to GENMASK_ULL and do a 32 bit build test.
I checked that the FIELD_GET would be fine, but forgot to look at
GENMASK.

oops.

Jonathan

> 
> Yours,
> Linus Walleij