From 122c234ef4e182440f8a60490e9344bfc4e2b5e9 Mon Sep 17 00:00:00 2001 From: Baruch Siach Date: Sun, 1 Sep 2024 09:12:34 +0300 Subject: [PATCH] arm64: mm: keep low RAM dma zone Commit ba0fb44aed47 ("dma-mapping: replace zone_dma_bits by zone_dma_limit") optimistically assumed that device-tree dma-ranges property describes the system DMA limits. That assumption ignores DMA limits of individual devices that are not encoded in device tree. Commit 833bd284a45 ("arm64: mm: fix DMA zone when dma-ranges is missing") fixed part of the problem for platforms that do not provide dma-ranges at all. However platforms like SM8550-HDK provide DMA bus limit, but have devices with stronger DMA limits. of_dma_get_max_cpu_address() does not take device limitations into account. These platforms implicitly rely on DMA zone in low 32-bit RAM area. Until we find a better way to figure out the optimal DMA zone range, restore the low RAM DMA zone we had before commit ba0fb44aed47. Fixes: ba0fb44aed47 ("dma-mapping: replace zone_dma_bits by zone_dma_limit") Closes: https://lore.kernel.org/r/1a0c7282-63e0-4add-8e38-3abe3e0a8e2f@linaro.org Reported-by: Neil Armstrong Reviewed-by: Catalin Marinas Suggested-by: Robin Murphy Signed-off-by: Baruch Siach Tested-by: Neil Armstrong # on SM8550-HDK Tested-by: Marek Szyprowski Signed-off-by: Christoph Hellwig --- arch/arm64/mm/init.c | 10 ++++++++-- 1 file changed, 8 insertions(+), 2 deletions(-) diff --git a/arch/arm64/mm/init.c b/arch/arm64/mm/init.c index 5710129b8033..eb76ac6d87c0 100644 --- a/arch/arm64/mm/init.c +++ b/arch/arm64/mm/init.c @@ -116,8 +116,14 @@ static void __init arch_reserve_crashkernel(void) static phys_addr_t __init max_zone_phys(phys_addr_t zone_limit) { - if (zone_limit == PHYS_ADDR_MAX) - zone_limit = U32_MAX; + /** + * Information we get from firmware (e.g. DT dma-ranges) describe DMA + * bus constraints. Devices using DMA might have their own limitations. + * Some of them rely on DMA zone in low 32-bit memory. Keep low RAM + * DMA zone on platforms that have RAM there. + */ + if (memblock_start_of_DRAM() < U32_MAX) + zone_limit = min(zone_limit, U32_MAX); return min(zone_limit, memblock_end_of_DRAM() - 1) + 1; }