Add the initialization function to create restricted DMA pools from
matching reserved-memory nodes.

Regardless of swiotlb setting, the restricted DMA pool is preferred if
available.

The restricted DMA pools provide a basic level of protection against the
DMA overwriting buffer contents at unexpected times. However, to protect
against general data leakage and system memory corruption, the system
needs to provide a way to lock down the memory access, e.g., MPU.

Signed-off-by: Claire Chang <redacted>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Tested-by: Stefano Stabellini <sstabellini@kernel.org>
Tested-by: Will Deacon <will@kernel.org>
---
 include/linux/swiotlb.h |  3 +-
 kernel/dma/Kconfig      | 14 ++++++++
 kernel/dma/swiotlb.c    | 76 +++++++++++++++++++++++++++++++++++++++++
 3 files changed, 92 insertions(+), 1 deletion(-)

diff --git a/include/linux/swiotlb.h b/include/linux/swiotlb.h
index 3b9454d1e498..39284ff2a6cd 100644
--- a/include/linux/swiotlb.h
+++ b/include/linux/swiotlb.h

@@ -73,7 +73,8 @@ extern enum swiotlb_force swiotlb_force;
  *		range check to see if the memory was in fact allocated by this
  *		API.
  * @nslabs:	The number of IO TLB blocks (in groups of 64) between @start and
- *		@end. This is command line adjustable via setup_io_tlb_npages.
+ *		@end. For default swiotlb, this is command line adjustable via
+ *		setup_io_tlb_npages.
  * @used:	The number of used IO TLB block.
  * @list:	The free list describing the number of free entries available
  *		from each index.

diff --git a/kernel/dma/Kconfig b/kernel/dma/Kconfig
index 77b405508743..3e961dc39634 100644
--- a/kernel/dma/Kconfig
+++ b/kernel/dma/Kconfig

@@ -80,6 +80,20 @@ config SWIOTLB
 	bool
 	select NEED_DMA_MAP_STATE
 
+config DMA_RESTRICTED_POOL
+	bool "DMA Restricted Pool"
+	depends on OF && OF_RESERVED_MEM
+	select SWIOTLB