Re: RFC: Memory region accesses where .valid.min_access_size < .impl.min_access_size

[Peter Maydell]

On Thu, 13 May 2021 at 12:49, Jonathan Cameron
<Jonathan.Cameron@huawei.com> wrote:
> My initial suggestion was to fix this by adding the relatively
> simple code needed in the driver to implement byte read / write,
> but Ben pointed at the QEMU docs - docs/devel/memory.rst which
> says
> "
> .impl.min_access_size, .impl.max_access_size define the access sizes
>    (in bytes) supported by the *implementation*; other access sizes will be
>    emulated using the ones available. For example a 4-byte write will be
>    emulated using four 1-byte writes, if .impl.max_access_size = 1.
> "
>
> This isn't true when we have the situation where
> .valid.min_access_size < .imp.min_access_size
>
> So change the docs or try to make this work?

I don't (yet) have a view on what the in-principle right thing
should be, but in practice: how many devices do we have which
set .valid.min_access_size < .imp.min_access_size ? If we want
to change the semantics we'd need to look at those to see if they
need to be adjusted (or if they're just currently buggy and would
be fixed by the change).

thanks
-- PMM