On Fri, Jun 13, 2025 at 02:54:50PM +0100, Robin Murphy wrote:

On 2025-06-12 7:56 pm, Nicolas Frattaroli wrote:

quoted

Hardware of various vendors, but very notably Rockchip, often uses
32-bit registers where the upper 16-bit half of the register is a
write-enable mask for the lower half.

This type of hardware setup allows for more granular concurrent register
write access.

Over the years, many drivers have hand-rolled their own version of this
macro, usually without any checks, often called something like
HIWORD_UPDATE or FIELD_PREP_HIWORD, commonly with slightly different
semantics between them.

Clearly there is a demand for such a macro, and thus the demand should
be satisfied in a common header file.

Add two macros: HWORD_UPDATE, and HWORD_UPDATE_CONST. The latter is a
version that can be used in initializers, like FIELD_PREP_CONST. The
macro names are chosen to not clash with any potential other macros that
drivers may already have implemented themselves, while retaining a
familiar name.

Nit: while from one angle it indeed looks similar, from another it's even
more opaque and less meaningful than what we have already. Personally I
cannot help but see "hword" as "halfword", so logically if we want 32+32-bit
or 8+8-bit variants in future those would be WORD_UPDATE() and
BYTE_UPDATE(), right? ;)

It's also confounded by "update" not actually having any obvious meaning at
this level without all the implicit usage context. FWIW my suggestion would
be FIELD_PREP_WM_U16, such that the reader instantly sees "FIELD_PREP with
some additional semantics", even if they then need to glance at the
kerneldoc for clarification that WM stands for writemask (or maybe WE for
write-enable if people prefer). Plus it then leaves room to easily support
different sizes (and potentially even bonkers upside-down Ux_WM variants?!)
without any bother if we need to.

I like the idea. Maybe even shorter: FIELD_PREP_WM16()?