linux-kernel - [PATCH] ARM/dma-mapping: invalidate caches on arch_dma_prep

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Message-ID: <43a834c8f871f8719368b3f3239f27ee4f6c6286.camel@gmail.com>
Date: Tue, 17 Jun 2025 09:54:46 +0200
From: Christian Meissl <meissl.christian@...il.com>
To: linux-arm-kernel@...ts.infradead.org
Cc: Russell King <linux@...linux.org.uk>, Christoph Hellwig <hch@....de>, 
 Philipp Zabel <p.zabel@...gutronix.de>, linux-kernel@...r.kernel.org,
 linux-media@...r.kernel.org
Subject: [PATCH] ARM/dma-mapping: invalidate caches on arch_dma_prep_coherent

since switching to dma-direct, memory using DMA_ATTR_NO_KERNEL_MAPPING
is no longer allocated using the arch specific handlers and instead
will use dma_direct_alloc_no_mapping. While the arm specific allocation
handlers implicitly clear the allocated dma buffers and will flush any caches
dma-direct relies on ARCH_HAS_DMA_PREP_COHERENT to flush the caches.

Without this flush video frame corruption can occur in drivers
like the coda v4l2 driver which explicitly sets the DMA_ATTR_NO_KERNEL_MAPPING flag.

Fixes: ae626eb97376 ("ARM/dma-mapping: use dma-direct unconditionally")
Signed-off-by: Christian Meissl <meissl.christian@...il.com>
---
 arch/arm/Kconfig          | 1 +
 arch/arm/mm/dma-mapping.c | 8 ++++++++
 2 files changed, 9 insertions(+)

diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
index 3072731fe09c..7a3aaf3a490b 100644
--- a/arch/arm/Kconfig
+++ b/arch/arm/Kconfig
@@ -14,6 +14,7 @@ config ARM
        select ARCH_HAS_DEBUG_VIRTUAL if MMU
        select ARCH_HAS_DMA_ALLOC if MMU
        select ARCH_HAS_DMA_OPS
+       select ARCH_HAS_DMA_PREP_COHERENT
        select ARCH_HAS_DMA_WRITE_COMBINE if !ARM_DMA_MEM_BUFFERABLE
        select ARCH_HAS_ELF_RANDOMIZE
        select ARCH_HAS_FORTIFY_SOURCE
diff --git a/arch/arm/mm/dma-mapping.c b/arch/arm/mm/dma-mapping.c
index 88c2d68a69c9..bde7ae4ba31a 100644
--- a/arch/arm/mm/dma-mapping.c
+++ b/arch/arm/mm/dma-mapping.c
@@ -1821,3 +1821,11 @@ void arch_dma_free(struct device *dev, size_t size, void *cpu_addr,
 {
        __arm_dma_free(dev, size, cpu_addr, dma_handle, attrs, false);
 }
+
+void arch_dma_prep_coherent(struct page *page, size_t size)
+{
+       void *ptr = page_address(page);
+
+       dmac_flush_range(ptr, ptr + size);
+       outer_flush_range(__pa(ptr), __pa(ptr) + size);
+}
-- 
2.49.0