Re: [PATCH 2/3] linux/bits.h: Add fixed-width GENMASK and BIT macros

Andy Shevchenko
2023-06-15T15:59:02Z

On Fri, May 12, 2023 at 09:29:23AM -0700, Lucas De Marchi wrote:
> On Fri, May 12, 2023 at 02:14:19PM +0300, Andy Shevchenko wrote:
> > On Mon, May 08, 2023 at 10:14:02PM -0700, Lucas De Marchi wrote:
> > > Add GENMASK_U32(), GENMASK_U16() and GENMASK_U8() macros to create
> > > masks for fixed-width types and also the corresponding BIT_U32(),
> > > BIT_U16() and BIT_U8().
> >
> > Why?
>
> to create the masks/values for device registers that are
> of a certain width, preventing mistakes like:
>
> #define REG1 0x10
> #define REG1_ENABLE BIT(17)
> #define REG1_FOO GENMASK(16, 15);
>
> register_write(REG1_ENABLE, REG1);
>
>
> ... if REG1 is a 16bit register for example. There were mistakes in the
> past in the i915 source leading to the creation of the REG_* variants on
> top of normal GENMASK/BIT (see last patch and commit 09b434d4f6d2
> ("drm/i915: introduce REG_BIT() and REG_GENMASK() to define register
> contents")

Doesn't it look like something for bitfield.h candidate?
If your definition doesn't fit the given mask, bail out.

--
With Best Regards,
Andy Shevchenko