Am 18.05.21 um 14:04 schrieb Thomas Hellström:
On 5/18/21 1:55 PM, Christian König wrote:
Am 18.05.21 um 10:26 schrieb Thomas Hellström:
The internal ttm_bo_util memcpy uses vmap functionality, and while it
probably might be possible to use it for copying in- and out of
sglist represented io memory, using io_mem_reserve() / io_mem_free()
callbacks, that would cause problems with fault().
Instead, implement a method mapping page-by-page using kmap_local()
semantics. As an additional benefit we then avoid the occasional global
TLB flushes of vmap() and consuming vmap space, elimination of a
critical
point of failure and with a slight change of semantics we could also
push
the memcpy out async for testing and async driver develpment purposes.
Pushing out async can be done since there is no memory allocation
going on
that could violate the dma_fence lockdep rules.
For copies from iomem, use the WC prefetching memcpy variant for
additional speed.
Note that drivers that don't want to use struct io_mapping but
relies on
memremap functionality, and that don't want to use scatterlists for
VRAM may well define specialized (hopefully reusable) iterators for
their
particular environment.
In general yes please since I have that as TODO for TTM for a very
long time.
But I would prefer to fix the implementation in TTM instead and give
it proper cursor handling.
Amdgpu is also using page based iomem and we are having similar
workarounds in place there as well.
I think it makes sense to unify this inside TTM and remove the old
memcpy util function when done.
Regards,
Christian.
Christian,
I was thinking when we replace the bo.mem with a pointer (and perhaps
have a driver callback to allocate the bo->mem,
we could perhaps embed a struct ttm_kmap_iter and use it for all
mapping in one way or another). That would mean perhaps land this is
i915 now and sort out the unification once the struct ttm_resource,
struct ttm_buffer_object separation has landed?
That stuff is ready, reviewed and I'm just waiting for some amdgpu
changes to land in drm-misc-next to push it.
But yes in general an iterator for the resource object sounds like the
right plan to me as well.
Christian.
/Thomas
