On Wed, Aug 19, 2020 at 09:14:31PM -0700, Moritz Fischer wrote: > On Thu, Aug 13, 2020 at 05:04:09PM +0800, Xu Yilun wrote: > > 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. > > Sorry for the delay, can you send a follow-up please? Hi moritz: I think I don't have to change it now. As discussed with David, these fields aren't often accessed. So it should be OK. Thanks, Yilun. > > Cheers, > Moritz
