Re: Allocating Qbus memory space and Qbus map space

[Matt Thomas <matt%3am-software.com@localhost>]

> On Jun 12, 2015, at 7:29 PM, Charles Dickman <chd%chdickman.com@localhost> wrote:
> 
> I can't find how the kernel handles allocation of Qbus memory space.
> 
> Qbus memory space that is not used by Qbus modules is part of the Qbus
> map and used for Qbus DMA mapping. Qbus memory space (a frame buffer
> for example) that is used by a Qbus module must be removed from the
> Qbus memory space usable for DMA.
> 
> Any thoughts on how this should be handled properly.

There should be an extent for the Q-bus memory in bus_dma_tag_t for
that q-bus (_sgmap->aps_ex).

Use it with 

extent_alloc_region(dmat->_sgmap->aps_ex, vastart, vaend, EX_WAITOK);

Thinking about this, bus_space_map on the iot should allocate the same
address region from the sgmap.  That it does not is a bug.

Or the uba attach code should probe each page and if does
not timeout, mark it as mappable.