On Tue, Oct 07, 2025 at 07:36:21PM +0900, Alexandre Courbot wrote: > Hi Yuri, > > On Tue Oct 7, 2025 at 7:29 AM JST, Yury Norov wrote: > <snip> > > Regardless, I don't think that this is the right path to move the > > bitfields into the core. The natural path for a feature that has > > been originally developed on driver side is to mature in there and > > get merged to core libraries after a while. Resctrl from Intel is one > > recent example. > > > > With that said, I'm OK if you move the bitfields as a whole, like you > > do in v5, and I'm also OK if you split out the part essential for nova > > and take it into the driver. In that case the bitfields will stay in > > drivers and you'll be able to focus on the features that _you_ need, > > not on generic considerations. > > > > I'm not OK to move bitfields in their current (v6) incomplete form in > > rust/kernel. We still have no solid understanding on the API and > > implementation that we've been all agreed on. > > Initially the plan was indeed to give this code some more time to mature > in nova-core before moving it out. > > The reason for the early move is that we have another driver (Tyr) who > wants to start using the register macro. Without it, they would be left > with the option of either reinventing the wheel, or poking at registers > the old-fashioned way, which I think we can agree is not going to be any > safer than the current macro. :) > > IIUC your remaining concern is with the possible loss of data when > setting a field that is smaller than its primitive type? That should be > addressed by [0], but as it introduces a new core feature I expect some > discussion to take place before it can be merged. In the meantime, it > would be great if we can make the register macro available. > > Because letting it fully mature within nova-core also has the drawback > that we might miss the perspective of other potential users, which may > make us draw ourselves into a corner that will make the macro less > useful generally speaking. We are at a stage where we can still make > design changes if needed, but we need to hear from other users, and > these won't come as long as the macro is in nova-core.
Hi Alexandre, Thanks for the broader perspective. So if there's another user for register!(), then yeah - it's worth to move it out of the nova earlier. It doesn't mean that we need to split bitfields out of it immediately. > [0] > https://lore.kernel.org/rust-for-linux/[email protected]/ This resembles the _BitInt from C23 standard, and it looks quite reasonable to me. I'll get back to your RFC shortly. https://en.cppreference.com/w/c/language/arithmetic_types.html -- I'm glad that we started this discussion. From my point, what happens now is inventing the whole new language, and basic bit operations is the heart of it. I would really like to avoid adopting an API that will frustrate people for decades after invention. Please read the following rant to taste exactly what I mean: https://lore.kernel.org/all/CAHk-=whoOUsqPKb7OQwhQf9H_3=5sxgpjrdbfqfwlb3bi13...@mail.gmail.com/ Thanks, Yury
