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Re: [Qemu-devel] [PATCH 1/2] Type-safe ioport callbacks


From: Blue Swirl
Subject: Re: [Qemu-devel] [PATCH 1/2] Type-safe ioport callbacks
Date: Tue, 26 Oct 2010 15:09:43 +0000

On Tue, Oct 26, 2010 at 8:05 AM, Avi Kivity <address@hidden> wrote:
>  On 10/25/2010 08:38 PM, Blue Swirl wrote:
>>
>> >
>> >  I don't really see why we need registration; cpu_register_io() takes
>> >  function pointers, a size, and an opaque, and gives an integer handle
>> > in
>> >  return.  With the IOPort object approach, you set up the IOPort with
>> >  function pointers, size is implied, and the opaque is derived using
>> >  container_of(); the handle is simply the address of the object.
>>
>> With the handle, we can separate setting up the structures at device
>> level, and mapping the object using only the handle at bus or other
>> higher level. Can this be done with the object approach?
>
> I believe so.  The handle is simply an indirect pointer, no?

Yes, but then the object should also contain size information. That
should not be needed for mapping at higher level.

>> The purpose of that patch series was to perform the separation for PCI
>> BARs. I wasn't so happy with the series, so I never pushed.
>
> In fact I think an IOPort is even more suitable; if we need additional
> attributes we can use a derived object:
>
> struct PCIIOPort {
>    IOPort ioport;
>    /* additional fields */
> };

One issue with my series was that it would be great if the devices
just had some BAR structures (used by PCI layer to map the devices)
inside PCI/qdev structures, but I invented that too late. Maybe this
can be addressed in your design?



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