On 2011-09-19 14:42, Avi Kivity wrote:
> 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".This has pros and cons. If you have n registers to dispatch, you then have to write n function prologues and maybe epilogues instead of just one. Specifically if the register access is trivial, that could case quite some LoC blowup on the device side. What may have a better ratio are generic register get/set handlers. Jan
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