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new 2cb7b7c03e1 arch/arm/stm32h7: invalidate dcache after aligned SDMMC RX
DMA
2cb7b7c03e1 is described below
commit 2cb7b7c03e1aecb85d9fbf568ee50cd10349fc49
Author: Yang-Rui Li <[email protected]>
AuthorDate: Thu Jul 23 12:00:57 2026 +0800
arch/arm/stm32h7: invalidate dcache after aligned SDMMC RX DMA
The aligned direct-DMA receive path only invalidated the destination
buffer before the transfer in stm32_dmarecvsetup(). On the Cortex-M7
the cache can speculatively prefetch into that cacheable buffer
between the pre-DMA invalidate and DMA completion, leaving stale
lines that shadow the data just written by the IDMA, so the CPU
reads a previously cached sector instead of the freshly received
data.
Invalidate again in stm32_recvdma() once the aligned transfer
completes, before the buffer is consumed. The buffer and length are
cache-line aligned on this path, so no adjacent memory is affected.
This matches the STM32 AN4839 guidance that a cache invalidate is
required after DMA completion and before the CPU reads the updated
region, not only before the transfer starts. A related instance of
the same "invalidate too early" defect on STM32H7 SPI DMA is tracked
in apache/nuttx#11594.
Root-caused on a PX4 FMUv6C (STM32H743) board where MAVLink ULog
downloads were intermittently corrupted: forensic diffing showed
corrupted windows were exactly 32 bytes (the D-cache line size),
cache-line aligned, and byte-for-byte equal to the previous 512-byte
SD sector cached in the FAT single-sector buffer. Disabling the
D-cache made the corruption disappear, isolating the defect to cache
coherency. After this fix, downloaded files matched the source file
byte-for-byte (sha256 identical) across a 5.8 MB log spanning
thousands of sectors.
Co-Authored-By: Claude Fable 5 <[email protected]>
Signed-off-by: Yang-Rui Li <[email protected]>
---
arch/arm/src/stm32h7/stm32_sdmmc.c | 17 ++++++++++++++++-
1 file changed, 16 insertions(+), 1 deletion(-)
diff --git a/arch/arm/src/stm32h7/stm32_sdmmc.c
b/arch/arm/src/stm32h7/stm32_sdmmc.c
index f1419f258c8..0383dbfa8d9 100644
--- a/arch/arm/src/stm32h7/stm32_sdmmc.c
+++ b/arch/arm/src/stm32h7/stm32_sdmmc.c
@@ -1359,7 +1359,22 @@ static void stm32_recvdma(struct stm32_dev_s *priv)
}
else
{
- /* In an aligned case, we have always received all blocks */
+ /* In an aligned case, we have always received all blocks.
+ *
+ * The destination buffer was invalidated before the DMA in
+ * stm32_dmarecvsetup(), but on the Cortex-M7 the cache can
+ * speculatively prefetch into this (cacheable) buffer between that
+ * point and DMA completion, leaving stale lines that shadow the
+ * data just written by the IDMA. Invalidate again now that the
+ * transfer is complete, before the buffer is consumed, so the CPU
+ * reads the freshly received data instead of a previously cached
+ * sector. The buffer and length are cache-line aligned here (that
+ * is why this aligned path was taken), so no adjacent memory is
+ * affected.
+ */
+
+ up_invalidate_dcache((uintptr_t)priv->buffer,
+ (uintptr_t)priv->buffer + priv->receivecnt);
priv->remaining = 0;
}
