[PATCH v4 2/5] dma: swiotlb: Centralize minimal pool sizing

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

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.

NOTE: We lose the RISC-V SWIOTLB_ANY setting in this patch. It will be
reinstated in a follow-up patch where we make SWIOTLB_ANY redundant.

Signed-off-by: Aneesh Kumar K.V (Arm) <aneesh.kumar@kernel.org>
---
 arch/arm64/mm/init.c | 11 -----------
 arch/riscv/mm/init.c | 20 --------------------
 kernel/dma/swiotlb.c | 18 ++++++++++++++++--
 3 files changed, 16 insertions(+), 33 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..734712230f35 100644
--- a/arch/riscv/mm/init.c
+++ b/arch/riscv/mm/init.c
@@ -165,31 +165,11 @@ static void print_vm_layout(void) { }
 
 void __init arch_mm_preinit(void)
 {
-	bool swiotlb = max_pfn > PFN_DOWN(dma32_phys_limit) &&
-		       memblock_start_of_DRAM() < dma32_phys_limit;
 	unsigned int swiotlb_flags = SWIOTLB_VERBOSE;
 #ifdef CONFIG_FLATMEM
 	BUG_ON(!mem_map);
 #endif /* CONFIG_FLATMEM */
 
-	if (IS_ENABLED(CONFIG_DMA_BOUNCE_UNALIGNED_KMALLOC) && !swiotlb &&
-	    dma_cache_alignment != 1) {
-		/*
-		 * No 32-bit DMA bouncing needed (either all DRAM is within
-		 * the 32-bit limit, or it all starts above it), but
-		 * kmalloc() buffers whose sizes are not cache-line-aligned
-		 * still require bouncing for non-coherent DMA.  Use
-		 * SWIOTLB_ANY so that the buffer can be allocated from high
-		 * 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;
-	}
-
 	if ((max_pfn > PFN_DOWN(dma32_phys_limit)) &&
 	     (memblock_start_of_DRAM() < dma32_phys_limit))
 		swiotlb_flags |= SWIOTLB_INIT_ADDRESSING_LIMIT;
diff --git a/kernel/dma/swiotlb.c b/kernel/dma/swiotlb.c
index aa19e81ae544..90e0bfd0715c 100644
--- a/kernel/dma/swiotlb.c
+++ b/kernel/dma/swiotlb.c
@@ -304,6 +304,11 @@ unsigned long swiotlb_size_or_default(void)
 	return default_nslabs << IO_TLB_SHIFT;
 }
 
+static bool __init swiotlb_default_size_changed(void)
+{
+	return default_nslabs != IO_TLB_DEFAULT_SIZE >> IO_TLB_SHIFT;
+}
+
 void __init swiotlb_adjust_size(unsigned long size)
 {
 	/*
@@ -311,7 +316,7 @@ void __init swiotlb_adjust_size(unsigned long size)
 	 * architectures such as those supporting memory encryption to
 	 * adjust/expand SWIOTLB size for their use.
 	 */
-	if (default_nslabs != IO_TLB_DEFAULT_SIZE >> IO_TLB_SHIFT)
+	if (swiotlb_default_size_changed())
 		return;
 
 	default_nslabs = swiotlb_aligned_nslabs(size);
@@ -476,9 +481,18 @@ 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