bus_dmamap_sync() for bounced client buffers from user address space

[Konstantin Belousov]

On Wed, Apr 29, 2015 at 12:22:19PM +0200, Svatopluk Kraus wrote:
> If using unmapped buffers is the way we will take to play with user
> space buffers, then:
> 
> (1) DMA clients, which support DMA for user space buffers, must use
> some variant of _bus_dmamap_load_phys(). They must wire physical pages
> in system anyway.
No, vm_fault_quick_hold_pages() + bus_dmamap_load_ma().
Or yes, if you count bus_dmamap_load_ma() as a variant of _load_phys().
I do not.

> (2) Maybe some better way how to temporarily allocate KVA for unmapped
> buffers should be implemented.
See some other mail from me about non-blocking sfbuf allocator with
callback.

> (3) DMA clients which already use _bus_dmamap_load_uio() with
> UIO_USERSPACE must be reimplemented or made obsolete.
Yes.

> (4) UIO_USERSPACE must be off limit in _bus_dmamap_load_uio() and man
> page should be changed according to it.
Yes.

> (5) And pmap can be deleted from struct bus_dmamap and all functions
> which use it as argument. Only kernel pmap will be used in DMA
> framework.
Probably yes.

> 
> Did I miss out something?
> 
> 
> > --
> > John Baldwin