On Wed, Jul 10, 2019 at 11:17:31AM +0200, Johannes Berg wrote: > On Tue, 2019-07-09 at 22:04 -0700, Joe Perches wrote: > > These GENMASK uses are inverted argument order and the > > actual masks produced are incorrect. Fix them. > > > > Add checkpatch tests to help avoid more misuses too. > > > > Joe Perches (12): > > checkpatch: Add GENMASK tests > > IMHO this doesn't make a lot of sense as a checkpatch test - just throw > in a BUILD_BUG_ON()? My personal take on this is that GENMASK() is really not useful, it's just pure obfuscation and leads to exactly these kinds of mistakes. Yes, I fully understand the argument that you can just specify the start and end bits, and it _in theory_ makes the code more readable. However, the problem is when writing code. GENMASK(a, b). Is a the starting bit or ending bit? Is b the number of bits? It's confusing and causes mistakes resulting in incorrect code. A BUILD_BUG_ON() can catch some of the cases, but not all of them. For example: GENMASK(6, 2) would satisify the requirement that a > b, so a BUILD_BUG_ON() will not trigger, but was the author meaning 0x3c or 0xc0? Personally, I've decided I am _not_ going to use GENMASK() in my code because I struggle to get the macro arguments correct - I'm _much_ happier, and it is way more reliable for me to write the mask in hex notation. I think this is where use of a ternary operator would come in use. The normal way of writing a number of bits tends to be "a:b", so if GENMASK took something like GENMASK(6:2), then I'd have less issue with it, because it's argument is then in a familiar notation. Yes, I'm sure that someone will point out that the GENMASK arguments are just in the same order, but that doesn't prevent _me_ frequently getting it wrong - and that's the point. The macro seems to me to cause more problems than it solves. -- RMK's Patch system: https://www.armlinux.org.uk/developer/patches/ FTTC broadband for 0.8mile line in suburbia: sync at 12.1Mbps down 622kbps up According to speedtest.net: 11.9Mbps down 500kbps up
