Re: [Qemu-devel] [PATCH v2 1/2] memory: Fix old portio word accesses

[Avi Kivity <avi@redhat.com>]

On 09/19/2011 03:32 PM, Jan Kiszka wrote:
> >  It's opt-in.  If a device sets
> >  MemoryRegionOps::impl.{min,max}_access_size = 1, it will only be fed
> >  byte accesses (the core will take care of breaking apart larger
> >  writes).  If it sets MemoryRegionOps::impl.{min,max}_access_size = 4, it
> >  will only get long accesses (and the core will/should shift/mask or
> >  RMW).  Refusing illegal access sizes is done using
> >  MemoryRegionOps::valid.  Most of this is unimplemented unfortunately.
>
> That makes sense (for non-old_portio users).
>
>

The trick of having a way to register N callbacks with one shot is worth 
growing.  Ideally each register in a BAR would have a callback and we'd 
do something like

     MemoryRegionOps mydev_ops = {
         .registers = {
              { MYDEV_REG_x, 4, 4, mydev_reg_x_read, mydev_reg_x_write, },
              ...
          },
     }

with hints to the core like "this register sits at this offset, use it 
for reads instead of a callback", or, "this is a read-only register".

-- 
error compiling committee.c: too many arguments to function