Re: [PATCH] xen/arm: debug-pl011: Use 32-bit accessors for broader compatibility

[Julien Grall <julien@xxxxxxx>]

On 06/06/2023 08:04, Michal Orzel wrote:
> Hi Julien,
Hi Michal,

> On 05/06/2023 20:34, Julien Grall wrote:
> I can think of the following patches:
> 1) Use correct accessors for early pl011 on arm32 and arm64
> - this would use the accessors depending on the given register size (ldrh, 
> strh, strb)
> - this would switch arm32 from 32-bit only to the same behavior as arm64
>
> 2) Support for 32-bit only PL011 in early pl011 on arm32 and arm64:
> - this would result in overwriting the changes done in patch 1 (but I'd prefer 
> not to do all in one patch for better history/backporting)
> as I'd have to introduce some macros e.g. PL011_STRH that would be defined as 
> strh in normal case and str in mmio32 case, etc. I could also
> just duplicate all the early functions and use ifdefery if that's what would be 
> preferred.
I would be fine with introduce PL011_STRH & co.

> 3) Use correct accessors for runtime pl011:
> I would prefer to do what Linux does meaning using the largest-common accessor 
> in normal-case (i.e. readw/writew) so that we can have a generic helpers
> (i.e. use readl/writel in mmio32 case or readw/writew in normal case). 
> Otherwise we would have to use the accessors depending on the given register 
> size
> (like in early printk) which destroys the idea of generic helpers. Linux for 
> earlycon also uses per-register size accessor and in runtime - largest-common.
Make senses.

Cheers,

--
Julien Grall