On Thu, Aug 13, 2020 at 08:28:05AM +0000, David Laight wrote: > From: Xu Yilun > > Sent: 13 August 2020 08:59 > > On Wed, Aug 12, 2020 at 08:52:39AM +0000, David Laight wrote: > > > From: Moritz Fischer > > > > Sent: 12 August 2020 04:56 > > > > > > > > On Mon, Aug 10, 2020 at 10:41:10AM +0800, Xu Yilun wrote: > > > > > The feature id is stored in a 12 bit field in DFH. So a u16 variable is > > > > > enough for feature id. > > > > > > > > > > This patch changes all feature id related places to fit u16. > > > > > > How much bigger does it make the kernel? > > > > The patch changes the definition of feature id from u64 to u16, and will > > make the kernel slightly smaller. > > Unlikely. > Most of the structures will gain a 'pad' field. > Using u16 for function parameters and results almost certainly > requires instructions to mask the value. > Any arithmetic on u16 will require masking instructions on > (probably) all architectures except x86. > > Using 'unsigned int' is probably best. > > u16 is never a good idea unless you are defining enough > of them in a structure (eg as an array) to reduce the > structure size below some threshold. > (Or are matching some hardware layout.) I got it. Thanks for your detailed explanation. I think we may change them to u32. Is it the same case for u8? Think we may also change the dfl_device_id.type. Hi Moritz: The patch is applied to for-next, is it possible we recall it, or we make another fix after it? Thanks, Yilun. > > David > > - > Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK > Registration No: 1397386 (Wales)
