On Tue, 2023-09-12 at 09:06 +0200, Christian König wrote:
External email : Please do not click links or open attachments until you have verified the sender or the content. Am 11.09.23 um 20:29 schrieb John Stultz:
On Mon, Sep 11, 2023 at 3:14 AM Christian König christian.koenig@amd.com wrote:
Am 11.09.23 um 04:30 schrieb Yong Wu:
From: John Stultz jstultz@google.com
This allows drivers who don't want to create their own DMA-BUF exporter to be able to allocate DMA-BUFs directly from existing DMA-BUF Heaps.
There is some concern that the premise of DMA-BUF heaps is that userland knows better about what type of heap memory is needed for a pipeline, so it would likely be best for drivers to import and fill DMA-BUFs allocated by userland instead of allocating one themselves, but this is still up for debate.
The main design goal of having DMA-heaps in the first place is to
avoid
per driver allocation and this is not necessary because userland
know
better what type of memory it wants.
The background is rather that we generally want to decouple
allocation
from having a device driver connection so that we have better
chance
that multiple devices can work with the same memory.
Yep, very much agreed, and this is what the comment above is trying
to describe.
Ideally user-allocated buffers would be used to ensure driver's
don't
create buffers with constraints that limit which devices the
buffers
might later be shared with.
However, this patch was created as a hold-over from the old ION
logic
to help vendors transition to dmabuf heaps, as vendors had
situations
where they still wanted to export dmabufs that were not to be generally shared and folks wanted to avoid duplication of logic already in existing heaps. At the time, I never pushed it upstream
as
there were no upstream users. But I think if there is now a
potential
upstream user, it's worth having the discussion to better
understand
the need.
Yeah, that indeed makes much more sense.
When existing drivers want to avoid their own handling and move their memory management over to using DMA-heaps even for internal allocations then no objections from my side. That is certainly something we should aim for if possible.
Thanks.
But what we should try to avoid is that newly merged drivers provide both a driver specific UAPI and DMA-heaps. The justification that this makes it easier to transit userspace to the new UAPI doesn't really count.
That would be adding UAPI already with a plan to deprecate it and that is most likely not helpful considering that UAPI must be supported forever as soon as it is upstream.
Sorry, I didn't understand this. I think we have not change the UAPI. Which code are you referring to?
So I think this patch is a little confusing in this series, as I
don't
see much of it actually being used here (though forgive me if I'm missing it).
Instead, It seems it get used in a separate patch series here:
https://lore.kernel.org/all/20230911125936.10648-1-yunfei.dong@mediatek.com/
Please try to avoid stuff like that it is really confusing and eats reviewers time.
My fault, I thought dma-buf and media belonged to the different tree, so I send them separately. The cover letter just said "The consumers of the new heap and new interface are our codecs and DRM, which will be sent upstream soon", and there was no vcodec link at that time.
In the next version, we will put the first three patches into the vcodec patchset.
Thanks.
Regards, Christian.
Yong, I appreciate you sending this out! But maybe if the secure
heap
submission doesn't depend on this functionality, I might suggest moving this patch (or at least the majority of it) to be part of
the
vcodec series instead? That way reviewers will have more context
for
how the code being added is used?
Will do. Thanks.
thanks -john