[PATCH v4 4/8] swiotlb: add a flag whether a SWIOTLB is allowed to grow

[Petr Tesarik <petrtesarik@xxxxxxxxxxxxxxx>]

From: Petr Tesarik <petr.tesarik.ext@xxxxxxxxxx>

Mark the default SWIOTLB as able to grow and restricted DMA pools as
unable.

However, if the address of the default memory pool is explicitly queried,
make the default SWIOTLB also unable to grow. This is currently used to set
up PCI BAR movable regions on some Octeon MIPS boards which may not be able
to use a SWIOTLB pool elsewhere in physical memory. See octeon_pci_setup()
for more details.

If a remap function is specified, it must be also called on any dynamically
allocated pools, but there are some issues:

- The remap function may block, so it should not be called from an atomic
  context.
- There is no corresponding unremap() function if the memory pool is
  freed.
- The only in-tree implementation (xen_swiotlb_fixup) requires that the
  number of slots in the memory pool is a multiple of SWIOTLB_SEGSIZE.

Keep it simple for now and disable growing the SWIOTLB if a remap function
was specified.

Signed-off-by: Petr Tesarik <petr.tesarik.ext@xxxxxxxxxx>
---
 include/linux/swiotlb.h | 2 ++
 kernel/dma/swiotlb.c    | 4 ++++
 2 files changed, 6 insertions(+)

diff --git a/include/linux/swiotlb.h b/include/linux/swiotlb.h
index d669e11e2827..81f8c901e888 100644
--- a/include/linux/swiotlb.h
+++ b/include/linux/swiotlb.h
@@ -102,6 +102,7 @@ struct io_tlb_pool {
  * @debugfs:	The dentry to debugfs.
  * @force_bounce: %true if swiotlb bouncing is forced
  * @for_alloc:  %true if the pool is used for memory allocation
+ * @can_grow:	%true if more pools can be allocated dynamically.
  * @total_used:	The total number of slots in the pool that are currently used
  *		across all areas. Used only for calculating used_hiwater in
  *		debugfs.
@@ -114,6 +115,7 @@ struct io_tlb_mem {
 	struct dentry *debugfs;
 	bool force_bounce;
 	bool for_alloc;
+	bool can_grow;
 #ifdef CONFIG_DEBUG_FS
 	atomic_long_t total_used;
 	atomic_long_t used_hiwater;
diff --git a/kernel/dma/swiotlb.c b/kernel/dma/swiotlb.c
index a80b77de8829..16e5b9a82902 100644
--- a/kernel/dma/swiotlb.c
+++ b/kernel/dma/swiotlb.c
@@ -332,6 +332,7 @@ void __init swiotlb_init_remap(bool addressing_limit, unsigned int flags,
 
 	io_tlb_default_mem.force_bounce =
 		swiotlb_force_bounce || (flags & SWIOTLB_FORCE);
+	io_tlb_default_mem.can_grow = !remap;
 
 	if (!default_nareas)
 		swiotlb_adjust_nareas(num_possible_cpus());
@@ -399,6 +400,7 @@ int swiotlb_init_late(size_t size, gfp_t gfp_mask,
 		return 0;
 
 	io_tlb_default_mem.force_bounce = swiotlb_force_bounce;
+	io_tlb_default_mem.can_grow = !remap;
 
 	if (!default_nareas)
 		swiotlb_adjust_nareas(num_possible_cpus());
@@ -1074,6 +1076,7 @@ EXPORT_SYMBOL_GPL(is_swiotlb_active);
  */
 phys_addr_t default_swiotlb_start(void)
 {
+	io_tlb_default_mem.can_grow = false;
 	return io_tlb_default_pool.start;
 }
 
@@ -1236,6 +1239,7 @@ static int rmem_swiotlb_device_init(struct reserved_mem *rmem,
 					 false, nareas);
 		mem->force_bounce = true;
 		mem->for_alloc = true;
+		mem->can_grow = false;
 		mem->pool = pool;
 		mem->nslabs = nslabs;
 
-- 
2.25.1