Re: [Qemu-devel] [PATCH v2 1/3] edu: mmio: set 'max_access_size' to 8

[Li Qiang <liq3ea@gmail.com>]

Philippe Mathieu-Daudé <philmd@redhat.com> 于2019年4月21日周日 下午6:28写道：

> Hi Li,
>
> The patch title is not very descriptive, maybe "allow 64-bit access"
>
>
> On 4/20/19 6:14 PM, Li Qiang wrote:
> > The edu spec said, the MMIO area can be accessed by 8 bytes.
>
> or 64-bit...
>
> > However currently the 'max_access_size' is not so the MMIO
> > access dispatch can only access 4 bytes one time. This patch
>
> 32-bit
>
> > fixes this to respect the spec.
> >
> > Notice: here the 'min_access_size' is not a must, I set this
> > for completement.
>
> Which one? valid/impl? I think you can drop this comment from the commit
> description.
>
>
Both needed. from memory_access_size, if we has no valid.max_access_size,
this function will set it to 4.

static int memory_access_size(MemoryRegion *mr, unsigned l, hwaddr addr)
{
    unsigned access_size_max = mr->ops->valid.max_access_size;

    /* Regions are assumed to support 1-4 byte accesses unless
       otherwise specified.  */
    if (access_size_max == 0) {
        access_size_max = 4;
    }
   ...
}

>From access_with_adjusted_size, if we has no impl.max_access_size,
this function will set it to 4.

ps: I will appreciate if anyone can explain what's the meaning of valid and
impl's min/max_access_size
and how it affects the behavior.

Thanks,
Li Qiang

>
> > Signed-off-by: Li Qiang <liq3ea@163.com>
> > ---
> >  hw/misc/edu.c | 9 +++++++++
> >  1 file changed, 9 insertions(+)
> >
> > diff --git a/hw/misc/edu.c b/hw/misc/edu.c
> > index 91af452c9e..65fc32b928 100644
> > --- a/hw/misc/edu.c
> > +++ b/hw/misc/edu.c
> > @@ -289,6 +289,15 @@ static const MemoryRegionOps edu_mmio_ops = {
> >      .read = edu_mmio_read,
> >      .write = edu_mmio_write,
> >      .endianness = DEVICE_NATIVE_ENDIAN,
> > +    .valid = {
> > +        .min_access_size = 4,
>
> Per the spec, this is correct.
>
> > +        .max_access_size = 8,
>
> Correct.
>
> > +    },
> > +    .impl = {
> > +        .min_access_size = 4,
>
> OK.
>
> > +        .max_access_size = 8,
>
> Correct.
>
> > +    },
> > +
> >  };
> >
> >  /*
> >
>
> With title/description updated:
> Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
>
>