From: "Aneesh Kumar K.V (Arm)" <aneesh.kumar@kernel•org>
To: linux-arm-kernel@lists•infradead.org,
linux-kernel@vger•kernel.org, iommu@lists•linux.dev
Cc: Catalin Marinas <catalin.marinas@arm•com>,
Will Deacon <will@kernel•org>,
Marek Szyprowski <m.szyprowski@samsung•com>,
Robin Murphy <robin.murphy@arm•com>,
suzuki.poulose@arm•com, steven.price@arm•com,
"Aneesh Kumar K.V (Arm)" <aneesh.kumar@kernel•org>
Subject: [PATCH] arm64: swiotlb: Don’t shrink default buffer when bounce is forced
Date: Tue, 20 Jan 2026 12:31:02 +0530 [thread overview]
Message-ID: <20260120070102.182977-1-aneesh.kumar@kernel.org> (raw)
arm64 reduces the default swiotlb size (for unaligned kmalloc()
bouncing) when it detects that no swiotlb bouncing is needed.
If swiotlb bouncing is explicitly forced via the command line
(swiotlb=force), this heuristic must not apply. Add a swiotlb helper to
query the forced-bounce state and use it to skip the resize when
bouncing is forced.
Signed-off-by: Aneesh Kumar K.V (Arm) <aneesh.kumar@kernel•org>
---
arch/arm64/mm/init.c | 3 ++-
include/linux/swiotlb.h | 7 +++++++
kernel/dma/swiotlb.c | 5 +++++
3 files changed, 14 insertions(+), 1 deletion(-)
diff --git a/arch/arm64/mm/init.c b/arch/arm64/mm/init.c
index 524d34a0e921..7046241b47b8 100644
--- a/arch/arm64/mm/init.c
+++ b/arch/arm64/mm/init.c
@@ -345,7 +345,8 @@ void __init arch_mm_preinit(void)
flags |= SWIOTLB_FORCE;
}
- if (IS_ENABLED(CONFIG_DMA_BOUNCE_UNALIGNED_KMALLOC) && !swiotlb) {
+ if (IS_ENABLED(CONFIG_DMA_BOUNCE_UNALIGNED_KMALLOC) &&
+ !(swiotlb || force_swiotlb_bounce())) {
/*
* If no bouncing needed for ZONE_DMA, reduce the swiotlb
* buffer for kmalloc() bouncing to 1MB per 1GB of RAM.
diff --git a/include/linux/swiotlb.h b/include/linux/swiotlb.h
index 3dae0f592063..513a93dcbdbc 100644
--- a/include/linux/swiotlb.h
+++ b/include/linux/swiotlb.h
@@ -185,6 +185,7 @@ bool is_swiotlb_active(struct device *dev);
void __init swiotlb_adjust_size(unsigned long size);
phys_addr_t default_swiotlb_base(void);
phys_addr_t default_swiotlb_limit(void);
+bool force_swiotlb_bounce(void);
#else
static inline void swiotlb_init(bool addressing_limited, unsigned int flags)
{
@@ -234,6 +235,12 @@ static inline phys_addr_t default_swiotlb_limit(void)
{
return 0;
}
+
+static inline bool force_swiotlb_bounce(void)
+{
+ return false;
+}
+
#endif /* CONFIG_SWIOTLB */
phys_addr_t swiotlb_tbl_map_single(struct device *hwdev, phys_addr_t phys,
diff --git a/kernel/dma/swiotlb.c b/kernel/dma/swiotlb.c
index 0d37da3d95b6..85e31f228cc9 100644
--- a/kernel/dma/swiotlb.c
+++ b/kernel/dma/swiotlb.c
@@ -1646,6 +1646,11 @@ phys_addr_t default_swiotlb_base(void)
return io_tlb_default_mem.defpool.start;
}
+bool force_swiotlb_bounce(void)
+{
+ return swiotlb_force_bounce;
+}
+
/**
* default_swiotlb_limit() - get the address limit of the default SWIOTLB
*
--
2.43.0
next reply other threads:[~2026-01-20 7:01 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-01-20 7:01 Aneesh Kumar K.V (Arm) [this message]
2026-01-20 9:25 ` [PATCH] arm64: swiotlb: Don’t shrink default buffer when bounce is forced Anshuman Khandual
2026-01-20 13:20 ` Robin Murphy
2026-01-21 6:10 ` Aneesh Kumar K.V
2026-02-04 18:52 ` Catalin Marinas
2026-02-06 6:11 ` Aneesh Kumar K.V
2026-03-04 10:00 ` Marek Szyprowski
2026-03-17 5:29 ` Aneesh Kumar K.V
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