dma-buf: heaps: Support carved-out heaps and ECC related-flags

Hi,

This series is the follow-up of the discussion that John and I had a few
months ago here:

https://lore.kernel.org/all/CANDhNCquJn6bH3KxKf65BWiTYLVqSd9892-xtFDHHqqyrroCMQ@mail.gmail.com/

The initial problem we were discussing was that I'm currently working on
a platform which has a memory layout with ECC enabled. However, enabling
the ECC has a number of drawbacks on that platform: lower performance,
increased memory usage, etc. So for things like framebuffers, the
trade-off isn't great and thus there's a memory region with ECC disabled
to allocate from for such use cases.

After a suggestion from John, I chose to start using heap allocations
flags to allow for userspace to ask for a particular ECC setup. This is
then backed by a new heap type that runs from reserved memory chunks
flagged as such, and the existing DT properties to specify the ECC
properties.

We could also easily extend this mechanism to support more flags, or
through a new ioctl to discover which flags a given heap supports.

I submitted a draft PR to the DT schema for the bindings used in this
PR:
devicetree-org/dt-schema#138

Let me know what you think,
Maxime

To: Rob Herring <[email protected]>
To: Saravana Kannan <[email protected]>
To: Sumit Semwal <[email protected]>
To: Benjamin Gaignard <[email protected]>
To: Brian Starkey <[email protected]>
To: John Stultz <[email protected]>
To: T.J. Mercier <[email protected]>
To: Christian König <[email protected]>
Cc: Mattijs Korpershoek <[email protected]>
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Signed-off-by: Maxime Ripard <[email protected]>

---
Changes in v2:
- EDITME: describe what is new in this series revision.
- EDITME: use bulletpoints and terse descriptions.
- Link to v1: https://lore.kernel.org/r/[email protected]



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    "change-id": "20240515-dma-buf-ecc-heap-28a311d2c94e",
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        "[email protected]"
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Author: mripard