TTM and AGP conflicts

[Jerome Glisse]

On Wed, Jan 4, 2012 at 11:04 AM, James Simmons <jsimmons at infradead.org> wrote:
>
>> >> Attached is patch to fix this, so sorry about that, i must have lost my
>> >> agp change along the way when working on the patchset. This patch is not
>> >> extensively tested, i will do more testing tomorrow on more gpu, might
>> >> even found an nvidia agp i can try. Again sorry for breaking this.
>> >
>> > Thanks for the fix up. I was wondering if this purposed change could be
>> > done instead. Its the same as your fix up except that you pass in the
>> > ttm_buffer_object for tt_create. The reason is I really like to have the
>> > ability to have more than one back end to grab a bunch pf pages from.
>> > Currently its AGP or something else. On some of my embedded devices the
>> > AGP space is not very large and can be exhausted very quickly. Those
>> > embedded devices have DMA engines I could use instead.
>>
>> This change violate the layer separation ttm wish to preserve see :
>> http://www.mail-archive.com/dri-devel@lists.freedesktop.org/msg16443.html
>>
>> You can achieve what you want by either adding a new domain so you would have
>> system, vram, agp, pcidma and object can be bound to one and only one. Or you
>> can hack your own agp ttm backend that could bind bo to agp or pci or
>> both at the same time depending on what you want to achieve.
>
> The question is how does one know which domain you want in tt_create.
> Currenty drivers are using there dev_priv but if you have have more than
> one option available how does one choose? Would you be okay with passing
> in a domain flag?
>

Well i agree that something would be usefull there so the driver know
which bind/unbind function it should use. Thomas i would prefer
passing the bo to the tt_create callback but a flag is the minimum we
need.

Cheers,
Jerome