[Nouveau] [Mesa-dev] [PATCH v3 0/2] nouveau: support for custom VRAM domains

[Alexandre Courbot]

On Fri, Jun 19, 2015 at 9:38 PM, Ben Skeggs <skeggsb at gmail.com> wrote:
> On 19 June 2015 at 21:51, Martin Peres <martin.peres at free.fr> wrote:
>> On 19/06/2015 13:02, Alexandre Courbot wrote:
>>>
>>> New revision of this patchset that prevents VRAM objects from being
>>> allocated on VRAM-less systems like Tegra. This is required for Mesa
>>> to work on such systems.
>>>
>>> Changes since v2:
>>> - Use vram_size to detect systems without VRAM and set the correct
>>>    domain instead of expecting each chip to set its domain explicitly.
>>
>>
>> This question may have been asked a ton of times, but what is the difference
>> with the nvac (Ion)?
>>
>> Would the nvac have some reserved memory for its usage by the bios which
>> would then be used as "VRAM"?
> PFB on the dGPU IGPs has facilities to fake VRAM from an area of
> "stolen" system memory reserved by the SBIOS.  GK20A/GM20B do not do
> this, and require direct (or, via a mmu, whatever) access to system
> memory.

Exactly. While dGPU do actually carve out a range of system memory to
be exclusively used as "fake" VRAM, Tegra GPUs have access to the
whole system memory which is shared with the other IPs of the SoC,
which requires a different management strategy. Hence the choice to
simply wipe out the concept of VRAM and use everything as system
memory.