[PATCH v2 6/7] drm/panfrost: Add support for GPU heap allocations

[Alyssa Rosenzweig]

> Sorry, I was being sloppy again![1] I meant CPU mmapped. 

No worries, just wanted to check :)

> Apparently the blob in some cases creates a SAME_VA GROW_ON_GPF buffer -
> since SAME_VA means permanently mapped on the CPU this translated to
> mmapping a HEAP object. Why it does this I've no idea.

I'm not sure I follow. Conceptually, if you're permanently mapped,
there's nothing to grow, right? Is there a reason not to just disable
HEAP in this cases, i.e.:

	if (flags & SAME_VA)
		flags &= ~GROW_ON_GPF;

It may not be fully optimal, but that way the legacy code keeps working
and upstream userspace isn't held back :)

> The main use in the blob for
> this is being able to dump buffers when debugging (i.e. dump buffers
> before/after every GPU job). 

Could we disable HEAP support in userspace (not setting the flags) for
debug builds that need to dump buffers? In production the extra memory
usage matters, hence this patch, but in dev, there's plenty of memory to
spare.

> Ideally you also need a way of querying which pages have been backed
> by faults (much easier with kbase where that's always just the number
> of pages).

Is there a use case for this with one of the userland APIs? (Maybe
Vulkan?)
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