Re: [Qemu-devel] Memory API: handling unassigned physical memory

[Blue Swirl]

On Mon, Apr 30, 2012 at 14:33, Mark Cave-Ayland
<address@hidden> wrote:
> On 30/04/12 15:03, Peter Maydell wrote:
>
>>> Therefore I can't change it to my (modified) sbus_mmio_map() function
>>> because it would break other non-SPARC platforms, and AIUI there is
>>> nothing
>>> in the memory API that allows me to move a subregion to a different
>>> MemoryRegion parent, even if I can get a reference to it with
>>> sysbus_mmio_get_region() after the sysbus_mmio_map() call - or have I
>>> misunderstood something?
>>
>>
>> Init functions like esp_init should be purely convenience functions
>> which create, set properties on, and map the sysbus/qdev device. If
>> they make use of private knowledge about the internals of the device
>> then this is wrong and should be fixed. For esp_init() it looks like
>> the handling of dma_memory_read, dma_memory_write, dma_opaque, it_shift
>> and dma_enabled are wrong.
>>
>> If you fix that then you can just ignore the convenience function,
>> and create, configure and map the device as appropriate for you.
>
>
> Right I think I'm starting to understand this now - in which case it becomes
> a matter of just copying a handful of lines within sun4m which is more
> bearable.
>
> In your view, would a suitable fix be to change dma_memory_read,
> dma_memory_write, dma_opaque, it_shift and dma_enabled to be qdev properties
> and modify esp_init() to return the qdev reference so they can be set by the
> caller?

There's an ongoing work to introduce IOMMUs by changing how DMA work
and this could simplify the DMA part. There's no clean way to use
function pointers in qdev.

For it_shift, a qdev or QOM property should be OK.

The signal dma_enabled should be eventually replaced by a Pin.

>
>
> ATB,
>
> Mark.
>