Tiler heap growing requires some kernel driver involvement: when the
tiler runs out of heap memory, it will raise an exception which is
either directly handled by the firmware if some free heap chunks are
available in the heap context, or passed back to the kernel otherwise.
The heap helpers will be used by the scheduler logic to allocate more
heap chunks to a heap context, when such a situation happens.

Heap context creation is explicitly requested by userspace (using
the TILER_HEAP_CREATE ioctl), and the returned context is attached to a
queue through some command stream instruction.

All the kernel does is keep the list of heap chunks allocated to a
context, so they can be freed when TILER_HEAP_DESTROY is called, or
extended when the FW requests a new chunk.

v6:
- Add Maxime's and Heiko's acks

v5:
- Fix FIXME comment
- Add Steve's R-b

v4:
- Rework locking to allow concurrent calls to panthor_heap_grow()
- Add a helper to return a heap chunk if we couldn't pass it to the
  FW because the group was scheduled out

v3:
- Add a FIXME for the heap OOM deadlock
- Use the panthor_kernel_bo abstraction for the heap context and heap
  chunks
- Drop the panthor_heap_gpu_ctx struct as it is opaque to the driver
- Ensure that the heap context is aligned to the GPU cache line size
- Minor code tidy ups
Co-developed-by: Steven Price <steven.price@arm.com>
Signed-off-by: Steven Price <steven.price@arm.com>
Signed-off-by: Boris Brezillon <boris.brezillon@collabora.com>
Reviewed-by: Steven Price <steven.price@arm.com>
Acked-by: Maxime Ripard <mripard@kernel.org>
Acked-by: Heiko Stuebner <heiko@sntech.de>
Link: https://patchwork.freedesktop.org/patch/msgid/20240229162230.2634044-10-boris.brezillon@collabora.com