Unverified Commit dcb2743d authored by Jisheng Zhang's avatar Jisheng Zhang Committed by Palmer Dabbelt
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riscv: mm: still create swiotlb buffer for kmalloc() bouncing if required 



After commit f51f7a0f ("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: default avatarJisheng Zhang <jszhang@kernel.org>
Reviewed-by: default avatarAlexandre Ghiti <alexghiti@rivosinc.com>
Link: https://lore.kernel.org/r/20240325110036.1564-1-jszhang@kernel.org


Signed-off-by: default avatarPalmer Dabbelt <palmer@rivosinc.com>
parent 0fdbb063

arch/riscv/include/asm/cache.h

+1 −1
Original line number Diff line number Diff line
@@ -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
Original line number Diff line number Diff line
@@ -161,11 +161,25 @@ 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();