Jakub Kicinski <jakub.kicinski@xxxxxxxxxxxxx> writes: > Small improvement suggested by Daniel Borkmann - use > two underscore prefix. > > https://www.mail-archive.com/netdev@xxxxxxxxxxxxxxx/msg125423.html > > -- v6 blurb: > > This set moves to a global header file macros which I find > very useful and worth popularising. The basic problem is > that since C bitfields are not very dependable accessing > subfields of registers becomes slightly inconvenient. > It is nice to have the necessary mask and shift operations > wrapped in a macro and have that macro compute shift > at compilation time using FFS. > > My implementation follows what Felix Fietkau has done in > mt76. Hannes Frederic Sowa suggested more use of standard > Linux/GCC functions. Since the RFC I've also added a > compile-time check to validate that the value passed to > setters fits in the mask. > > I attempted the use of static inlines instead of macros > but it makes GCC < 6.0 barf at the BUILD_BUG_ON()s. > I also noticed that forcing arguments to be u32 for inlines > makes the compiler use 32bit arithmetic where it could > get away with 64bit before (on 64bit machines, obviously). > That's a potential performance concern but probably not > a very practical one today. Apart from looking "cleaner" > static inlines would have the advantage that we could #undef > the auxiliary macros at the end of the header. > > Build bot caught a build failure with -Os set. AFAICT gcc > did not handle temporary variable I put in the macro > expression too well. I work around that by defining > __BUILD_BUG_ON_NOT_POWER_OF_2 and using it instead of > BUILD_BUG_ON(!tmp || is_power_of_2(tmp)). > > I'm planning to use those macros in another driver soon, > Felix may also use them when upstreaming mt76 if he chooses > to do so. > > IMHO if accepted it would be best to push these through > Kalle's wireless drivers' tree, since the only existing > user is in drivers/net/wireless/. > > v8: > - use two underscores for auxiliary macros (Daniel B). > v7: > - drop the explicit type marking (u32/u64) - depend on the type > of the mask instead; > - only allow compilation time constant masks; > - barf at "type of register too small to ever match mask" on get; > - rename PUT -> PREP. > v6: > - do a full rename in patch 2; > - CC many people. > v5: > - repost. > v4: > - add documentation in the header. > v3: > - don't use variables in statement expressions; > - use __BUILD_BUG_ON_NOT_POWER_OF_2. > v2: > - change Felix's email address. > > Jakub Kicinski (4): > add basic register-field manipulation macros > mt7601u: remove redefinition of GENMASK > mt7601u: remove unnecessary include > mt7601u: use linux/bitfield.h I applied these now to the pending branch of my wireless-drivers-next tree. Let's see if the kbuild bot finds any problems. Please also CC lkml, did that now. -- Kalle Valo
