Re: [PATCH 1/2] rust: sizes: add u64 variants of SZ_* constants

[John Hubbard]

On 3/10/26 3:13 PM, John Hubbard wrote:
> On 3/10/26 3:08 PM, Miguel Ojeda wrote:
>> On Tue, Mar 10, 2026 at 9:55 PM Danilo Krummrich <dakr@xxxxxxxxxx> wrote:
>>>
>>> Forgot to mention, the background of this is that existing DRM components, such
>>> as GPUVM, Buddy, etc. just use u64 as a common denominator. However, this
>>> becomes annoying when the corresponding device is u32 (or even smaller outside
>>> of DRM). Because then we have all the fallible conversions on the other end
>>> where the driver interacts with the HW.
>>>
>>> So, on the Rust side I think we want to abstract this, such that drivers can
>>> choose the actual device size type and the corresponding APIs just work with
>>> this type and store the actual value in the backing u64 internally, but hand it
>>> out as the actual type the driver passed in originally.
>>
>> I see, thanks for that context -- yes, if the types are different and
>> known, it would be better to abstract over the right one.
>>
>> (And perhaps it may even make sense to use newtypes too, depending on
>> the details.)
> 
> It might. Because GpuAddr is a bit vague, whereas FbAddr is always going
> to be u64.
> 
> OK, I think a define_size!() macro that implements a DeviceSize trait works
> here. We still end up converting call sites to use sizes::u64::SZ_1M, once

ah, correction, make that u64::SZ_1M, when DeviceSize is in scope.
(No sizes:: prefix.)

> DeviceSize is in scope.
> 
> And then later, one can build on top of that with things such as
> <T: DeviceSize>, and such.
> 
> I'll post a v2, assuming that this sounds about right.
> 
> thanks,

thanks,
-- 
John Hubbard