[PATCH] arm64: swiotlb: Don’t shrink default buffer when bounce is forced

["Aneesh Kumar K.V (Arm)" <aneesh.kumar@kernel.org>]

arm64 reduces the default swiotlb size (for unaligned kmalloc()
bouncing) when it detects that no swiotlb bouncing is needed.

If swiotlb bouncing is explicitly forced via the command line
(swiotlb=force), this heuristic must not apply. Add a swiotlb helper to
query the forced-bounce state and use it to skip the resize when
bouncing is forced.

Signed-off-by: Aneesh Kumar K.V (Arm) <aneesh.kumar@kernel.org>
---
 arch/arm64/mm/init.c    | 3 ++-
 include/linux/swiotlb.h | 7 +++++++
 kernel/dma/swiotlb.c    | 5 +++++
 3 files changed, 14 insertions(+), 1 deletion(-)

diff --git a/arch/arm64/mm/init.c b/arch/arm64/mm/init.c
index 524d34a0e921..7046241b47b8 100644
--- a/arch/arm64/mm/init.c
+++ b/arch/arm64/mm/init.c
@@ -345,7 +345,8 @@ void __init arch_mm_preinit(void)
 		flags |= SWIOTLB_FORCE;
 	}
 
-	if (IS_ENABLED(CONFIG_DMA_BOUNCE_UNALIGNED_KMALLOC) && !swiotlb) {
+	if (IS_ENABLED(CONFIG_DMA_BOUNCE_UNALIGNED_KMALLOC) &&
+	    !(swiotlb || force_swiotlb_bounce())) {
 		/*
 		 * If no bouncing needed for ZONE_DMA, reduce the swiotlb
 		 * buffer for kmalloc() bouncing to 1MB per 1GB of RAM.
diff --git a/include/linux/swiotlb.h b/include/linux/swiotlb.h
index 3dae0f592063..513a93dcbdbc 100644
--- a/include/linux/swiotlb.h
+++ b/include/linux/swiotlb.h
@@ -185,6 +185,7 @@ bool is_swiotlb_active(struct device *dev);
 void __init swiotlb_adjust_size(unsigned long size);
 phys_addr_t default_swiotlb_base(void);
 phys_addr_t default_swiotlb_limit(void);
+bool force_swiotlb_bounce(void);
 #else
 static inline void swiotlb_init(bool addressing_limited, unsigned int flags)
 {
@@ -234,6 +235,12 @@ static inline phys_addr_t default_swiotlb_limit(void)
 {
 	return 0;
 }
+
+static inline bool force_swiotlb_bounce(void)
+{
+	return false;
+}
+
 #endif /* CONFIG_SWIOTLB */
 
 phys_addr_t swiotlb_tbl_map_single(struct device *hwdev, phys_addr_t phys,
diff --git a/kernel/dma/swiotlb.c b/kernel/dma/swiotlb.c
index 0d37da3d95b6..85e31f228cc9 100644
--- a/kernel/dma/swiotlb.c
+++ b/kernel/dma/swiotlb.c
@@ -1646,6 +1646,11 @@ phys_addr_t default_swiotlb_base(void)
 	return io_tlb_default_mem.defpool.start;
 }
 
+bool force_swiotlb_bounce(void)
+{
+	return swiotlb_force_bounce;
+}
+
 /**
  * default_swiotlb_limit() - get the address limit of the default SWIOTLB
  *
-- 
2.43.0