Hi, On Mon, Oct 27, 2025 at 11:02:48AM +0200, Jani Nikula wrote: > On Sat, 25 Oct 2025, "Yury Norov (NVIDIA)" <[email protected]> wrote: > > Standardize parameters ordering in some typical cases to minimize > > confusion. > > > > Signed-off-by: Yury Norov (NVIDIA) <[email protected]> > > --- > > Documentation/process/coding-style.rst | 48 ++++++++++++++++++++++++++ > > 1 file changed, 48 insertions(+) > > > > diff --git a/Documentation/process/coding-style.rst > > b/Documentation/process/coding-style.rst > > index d1a8e5465ed9..dde24148305c 100644 > > --- a/Documentation/process/coding-style.rst > > +++ b/Documentation/process/coding-style.rst > > @@ -523,6 +523,54 @@ below, compared to the **declaration** example above):: > > ... > > } > > > > +6.2) Function parameters order > > +------------------------------ > > + > > +The order of parameters is important both for code generation and > > readability. > > +Passing parameters in an unusual order is a common source of bugs. Listing > > +them in standard widely adopted order helps to avoid confusion. > > + > > +Many ABIs put first function parameter and return value in R0. If your > > +function returns one of its parameters, passing it at the very beginning > > +would lead to a better code generation. For example:: > > + > > + void *memset64(uint64_t *s, uint64_t v, size_t count); > > + void *memcpy(void *dest, const void *src, size_t count); > > + > > +If your function doesn't propagate a parameter, but has a meaning of > > copying > > +and/or processing data, the best practice is following the traditional > > order: > > +destination, source, options, flags. > > + > > +for_each()-like iterators should take an enumerator the first. For > > example:: > > + > > + for_each_set_bit(bit, mask, nbits); > > + do_something(bit); > > + > > + list_for_each_entry(pos, head, member); > > + do_something(pos); > > + > > +If function operates on a range or ranges of data, corresponding parameters > > +may be described as ``start - end`` or ``start - size`` pairs. In both > > cases, > > +the parameters should follow each other. For example:: > > + > > + int > > + check_range(unsigned long vstart, unsigned long vend, > > + unsigned long kstart, unsigned long kend); > > + > > + static inline void flush_icache_range(unsigned long start, > > unsigned long end); > > + > > + static inline void flush_icache_user_page(struct vm_area_struct > > *vma, > > + struct page *page, > > + unsigned long addr, int len); > > + > > +Both ``start`` and ``end`` of the interval are inclusive. > > + > > +Describing intervals in order ``end - start`` is unfavorable. One notable > > +example is the ``GENMASK(high, low)`` macro. While such a notation is > > popular > > +in hardware context, particularly to describe registers structure, in > > context > > +of software development it looks counter intuitive and confusing. Please > > switch > > +to an equivalent ``BITS(low, high)`` version. > > + > > GENMASK when used for defining hardware registers is completely fine, > and *much* easier to deal with when you cross check against the specs > that almost invariably define high:low.
I fully agree with Jani here! When coming into describing registers my brain is hardwired to read values from left to right, high-low. Linus suggested also BITS(start_bit, n_bits) which, in my opinion, complements what we already have. We leave GENMASK to register mask descriptions and BITS to the rest. Andi
