We must not unconditionally set the DMA snoop bit; if the DMA API is assuming that the device is not DMA coherent, and the device snoops the CPU caches, the device can see stale cache lines brought in by speculative prefetch. This leads to the device seeing stale data, potentially resulting in corrupted data transfers. Commonly, this results in a descriptor fetch error such as: mmc0: ADMA error mmc0: sdhci: ============ SDHCI REGISTER DUMP =========== mmc0: sdhci: Sys addr: 0x00000000 | Version: 0x00002202 mmc0: sdhci: Blk size: 0x00000008 | Blk cnt: 0x00000001 mmc0: sdhci: Argument: 0x00000000 | Trn mode: 0x00000013 mmc0: sdhci: Present: 0x01f50008 | Host ctl: 0x00000038 mmc0: sdhci: Power: 0x00000003 | Blk gap: 0x00000000 mmc0: sdhci: Wake-up: 0x00000000 | Clock: 0x000040d8 mmc0: sdhci: Timeout: 0x00000003 | Int stat: 0x00000001 mmc0: sdhci: Int enab: 0x037f108f | Sig enab: 0x037f108b mmc0: sdhci: ACmd stat: 0x00000000 | Slot int: 0x00002202 mmc0: sdhci: Caps: 0x35fa0000 | Caps_1: 0x0000af00 mmc0: sdhci: Cmd: 0x0000333a | Max curr: 0x00000000 mmc0: sdhci: Resp[0]: 0x00000920 | Resp[1]: 0x001d8a33 mmc0: sdhci: Resp[2]: 0x325b5900 | Resp[3]: 0x3f400e00 mmc0: sdhci: Host ctl2: 0x00000000 mmc0: sdhci: ADMA Err: 0x00000009 | ADMA Ptr: 0x000000236d43820c mmc0: sdhci: ============================================ mmc0: error -5 whilst initialising SD card but can lead to other errors, and potentially direct the SDHCI controller to read/write data to other memory locations (e.g. if a valid descriptor is visible to the device in a stale cache line.) Fix this by ensuring that the DMA snoop bit corresponds with the behaviour of the DMA API. Since the driver currently only supports DT, use of_dma_is_coherent(). Note that device_get_dma_attr() can not be used as that risks re-introducing this bug if/when the driver is converted to ACPI. Signed-off-by: Russell King <rmk+kernel@xxxxxxxxxxxxxxx> --- drivers/mmc/host/sdhci-of-esdhc.c | 7 ++++++- 1 file changed, 6 insertions(+), 1 deletion(-) diff --git a/drivers/mmc/host/sdhci-of-esdhc.c b/drivers/mmc/host/sdhci-of-esdhc.c index 4dd43b1adf2c..74de5e8c45c8 100644 --- a/drivers/mmc/host/sdhci-of-esdhc.c +++ b/drivers/mmc/host/sdhci-of-esdhc.c @@ -495,7 +495,12 @@ static int esdhc_of_enable_dma(struct sdhci_host *host) dma_set_mask_and_coherent(dev, DMA_BIT_MASK(40)); value = sdhci_readl(host, ESDHC_DMA_SYSCTL); - value |= ESDHC_DMA_SNOOP; + + if (of_dma_is_coherent(dev->of_node)) + value |= ESDHC_DMA_SNOOP; + else + value &= ~ESDHC_DMA_SNOOP; + sdhci_writel(host, value, ESDHC_DMA_SYSCTL); return 0; } -- 2.7.4
