Re: [PATCH v6 4/5] rust: Move register and bitfield macros out of Nova

[Dirk Behme <dirk.behme@gmail.com>]

On 09.10.25 13:28, Alexandre Courbot wrote:
> On Thu Oct 9, 2025 at 8:16 PM JST, Danilo Krummrich wrote:
>> On Thu Oct 9, 2025 at 8:59 AM CEST, Dirk Behme wrote:
>>> Assuming that register.rs is supposed to become the "generic" way to 
>>> access hardware registers I started to have a look to it. Some weeks 
>>> back testing interrupts I used some quite simple timer with 4 registers 
>>> [1]. Now, thinking about converting it to register!() I have three 
>>> understanding / usage questions:
>>>
>>> * At the moment register!() is for 32-bit registers, only? So it can't 
>>> be used for my example having 8-bit and 16-bit registers as well?
>>
>> Yes, currently the register!() macro always generates a 32-bit register type
>> (mainly because nova-core did not need anything else). However, this will of
>> course be generalized (which should be pretty straight forward).
>>
>> Having a brief look at the TMU datasheet it looks like you should be able to
>> treat TSTR and TCR as 32-bit registers without any issues for testing the
>> register!() macro today. I.e. you can just define it as:
>>
>> 	register!(TSTR @ 0x04, "Timer Start Register" {
>> 	    2:2    str2 as bool, "Specifies whether TCNT2 is operated or stopped.";
>> 	    1:1    str1 as bool, "Specifies whether TCNT1 is operated or stopped.";
>> 	    0:0    str0 as bool, "Specifies whether TCNT0 is operated or stopped.";
>> 	});
>>
>> Same for TCR.
> 
> Patch 2 of this series actually adds support for 16 and 8 bit register
> storage.

Hmm, how to use that with the register!() macro? I mean patch 2 adds
support for different storage widths for *bitfields*. But looking at
patch 4 [2] it looks like *register!()* still uses $name(u32)? With
that it looks like that the register!() macro still just supports 32
bit registers? Or what have I missed?

What I'm looking for is a way to specify if a register is 8, 16 or 32
bit. Using the example from above something like

register!(TSTR<u8> @ ....

Thanks

Dirk

[2]

https://lore.kernel.org/rust-for-linux/20251003154748.1687160-5-joelagnelf@nvidia.com/

...
+#[macro_export]
 macro_rules! register {
     // Creates a register at a fixed offset of the MMIO space.
     ($name:ident @ $offset:literal $(, $comment:literal)? {
$($fields:tt)* } ) => {
-        bitfield!(pub(crate) struct $name(u32) $(, $comment)? {
$($fields)* } );
+        ::kernel::bitfield!(pub(crate) struct $name(u32) $(,
$comment)? { $($fields)* } );
         register!(@io_fixed $name @ $offset);
     };
...