riscv: mm: still create swiotlb buffer for kmalloc() bouncing if required

PATCH Superseded Jisheng Zhang 1 participant 1 message Jan 25, 2024 RISC-V

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Jisheng Zhang

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2024-01-25 15:11 UTC #0 lore raw

PATCH v3 1/1 riscv: mm: still create swiotlb buffer for kmalloc() bouncing if required

After commit f51f7a0fc2f4 ("riscv: enable DMA_BOUNCE_UNALIGNED_KMALLOC for !dma_coherent"), for non-coherent platforms with less than 4GB memory, we rely on users to pass "swiotlb=mmnn,force" kernel parameters to enable DMA bouncing for unaligned kmalloc() buffers. Now let's go
further: If no bouncing needed for ZONE_DMA, let kernel automatically allocate 1MB swiotlb buffer per 1GB of RAM for kmalloc() bouncing on non-coherent platforms, so that no need to pass "swiotlb=mmnn,force" any more.

The math of "1MB swiotlb buffer per 1GB of RAM for kmalloc() bouncing" is taken from arm64. Users can still force smaller swiotlb buffer by passing "swiotlb=mmnn".

Signed-off-by Jisheng Zhang <[email protected]>

Reviewed-by Alexandre Ghiti <[email protected]>

---

since v2:
- rebase on v6.8-rc1
- collect Reviewed-by tag

since v1
- fix build error if CONFIG_RISCV_DMA_NONCOHERENT=n

 arch/riscv/include/asm/cache.h |  2 +-
 arch/riscv/mm/init.c           | 16 +++++++++++++++-
 2 files changed, 16 insertions(+), 2 deletions(-)

arch/riscv/include/asm/cache.h +1 -1

index 2174fe7bac9a..570e9d8acad1 100644
@@ -26,8 +26,8 @@
 
 #ifndef __ASSEMBLY__
 
-#ifdef CONFIG_RISCV_DMA_NONCOHERENT
 extern int dma_cache_alignment;
+#ifdef CONFIG_RISCV_DMA_NONCOHERENT
 #define dma_get_cache_alignment dma_get_cache_alignment
 static inline int dma_get_cache_alignment(void)
 {

arch/riscv/mm/init.c +15 -1

index 32cad6a65ccd..3359472df9a5 100644
@@ -162,11 +162,25 @@ static void print_vm_layout(void) { }
 
 void __init mem_init(void)
 {
+	bool swiotlb = max_pfn > PFN_DOWN(dma32_phys_limit);
 #ifdef CONFIG_FLATMEM
 	BUG_ON(!mem_map);
 #endif /* CONFIG_FLATMEM */
 
-	swiotlb_init(max_pfn > PFN_DOWN(dma32_phys_limit), SWIOTLB_VERBOSE);
+	if (IS_ENABLED(CONFIG_DMA_BOUNCE_UNALIGNED_KMALLOC) && !swiotlb &&
+	    dma_cache_alignment != 1) {
+		/*
+		 * If no bouncing needed for ZONE_DMA, allocate 1MB swiotlb
+		 * buffer per 1GB of RAM for kmalloc() bouncing on
+		 * non-coherent platforms.
+		 */
+		unsigned long size =
+			DIV_ROUND_UP(memblock_phys_mem_size(), 1024);
+		swiotlb_adjust_size(min(swiotlb_size_or_default(), size));
+		swiotlb = true;
+	}
+
+	swiotlb_init(swiotlb, SWIOTLB_VERBOSE);
 	memblock_free_all();
 
 	print_vm_layout();

Signature · 1 line

2.43.0