[PATCH v5 3/6] dma: swiotlb: Centralize minimal pool sizing

[Aneesh Kumar K.V (Arm)]

A default SWIOTLB pool used only for unaligned kmalloc bouncing can be
smaller than one required for limited DMA addressing. Arm64 and RISC-V
currently implement this sizing independently, using 1 MiB of SWIOTLB
space per GiB of RAM.

The SWIOTLB core now identifies this case with SWIOTLB_POOL_MINIMAL.
Size that policy in swiotlb_adjust_pool_size() and remove the
architecture-specific adjustments.

Explicit swiotlb= sizing remains unchanged because swiotlb_adjust_size()
preserves a user-configured size.

Signed-off-by: Aneesh Kumar K.V (Arm) <aneesh.kumar at kernel.org>
---
 arch/arm64/mm/init.c | 11 -----------
 arch/riscv/mm/init.c |  4 ----
 kernel/dma/swiotlb.c | 11 ++++++++++-
 3 files changed, 10 insertions(+), 16 deletions(-)

diff --git a/arch/arm64/mm/init.c b/arch/arm64/mm/init.c
index 7d51fb5f5a71..95075b5c8207 100644
--- a/arch/arm64/mm/init.c
+++ b/arch/arm64/mm/init.c
@@ -340,17 +340,6 @@ void __init arch_mm_preinit(void)
 {
 	unsigned int flags = SWIOTLB_VERBOSE;
 
-	if (max_pfn <= PFN_DOWN(arm64_dma_phys_limit)) {
-		/*
-		 * If no bouncing needed for ZONE_DMA, reduce the swiotlb
-		 * buffer for kmalloc() bouncing to 1MB per 1GB of RAM.
-		 */
-		unsigned long size =
-			DIV_ROUND_UP(memblock_phys_mem_size(), 1024);
-
-		swiotlb_adjust_size(min(swiotlb_size_or_default(), size));
-	}
-
 	if (max_pfn > PFN_DOWN(arm64_dma_phys_limit))
 		flags |= SWIOTLB_INIT_ADDRESSING_LIMIT;
 
diff --git a/arch/riscv/mm/init.c b/arch/riscv/mm/init.c
index e0e4c103d603..96856114b387 100644
--- a/arch/riscv/mm/init.c
+++ b/arch/riscv/mm/init.c
@@ -183,10 +183,6 @@ void __init arch_mm_preinit(void)
 		 * memory when DRAM starts above dma32_phys_limit.  Allocate
 		 * ~1 MB per 1 GB of RAM.
 		 */
-		unsigned long size =
-			DIV_ROUND_UP(memblock_phys_mem_size(), 1024);
-		swiotlb_adjust_size(min(swiotlb_size_or_default(), size));
-		swiotlb = true;
 		swiotlb_flags |= SWIOTLB_ANY;
 	}
 
diff --git a/kernel/dma/swiotlb.c b/kernel/dma/swiotlb.c
index 8f86deb25be2..f368a73f4ed0 100644
--- a/kernel/dma/swiotlb.c
+++ b/kernel/dma/swiotlb.c
@@ -483,9 +483,18 @@ static bool __init swiotlb_kmalloc_needs_bounce(void)
 static void __init
 swiotlb_adjust_pool_size(enum swiotlb_pool_policy policy)
 {
+	if (swiotlb_default_size_changed())
+		return;
+
 	switch (policy) {
-	case SWIOTLB_POOL_MINIMAL:
+	case SWIOTLB_POOL_MINIMAL: {
+		unsigned long size;
+
+		/* Use 1MB per 1GB of RAM for kmalloc() bouncing. */
+		size = DIV_ROUND_UP(memblock_phys_mem_size(), 1024);
+		swiotlb_adjust_size(min(swiotlb_size_or_default(), size));
 		break;
+	}
 	case SWIOTLB_POOL_CC_GUEST:
 		break;
 	case SWIOTLB_POOL_NONE:
-- 
2.43.0