Hello, On Friday, 13 June 2025 16:52:28 Central European Summer Time Yury Norov wrote: > On Fri, Jun 13, 2025 at 02:54:50PM +0100, Robin Murphy wrote: > > On 2025-06-12 7:56 pm, Nicolas Frattaroli wrote: > > > 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()? >
I do think FIELD_PREP_WM16() is a good name. If everyone is okay with this as a name, I will use it in v2 of the series. And by "everyone" I really mean everyone should get their hot takes in before the end of the week, as I intend to send out a v2 on either Friday or the start of next week to keep the ball rolling, but I don't want to reroll a 20 patch series with a trillion recipients more than is absolutely necessary. To that end, I'd also like to get some other naming choices clarified. As I gathered, these two macros should best be placed in its own header. Is include/linux/hw_bitfield.h a cromulent choice, or should we go with include/linux/hw_bits.h? Furthermore, should it be FIELD_PREP_WM16_CONST or FIELD_PREP_CONST_WM16? I'm personally partial to the former. And finally, is it okay if I leave out refactoring Intel's _MASKED_FIELD() or should I see if I can at least replace its implementation while I'm at it? For less opinionated changes, I'll also change all the `U` literal suffixes to `UL` wherever I've added them. As I understand it, it doesn't really make a difference in these instances, but `UL` is more prevalent in the kernel. Kind regards, Nicolas Frattaroli
