[PATCH] pci: designware: Set DMA_BYPASS bit in outbound IATU CTRL2 register

[PATCH] pci: designware: Set DMA_BYPASS bit in outbound IATU CTRL2 register

[Sumit Kumar]

Outbound IATU apertures are configured with local device-side addresses.
When DMA engine transactions use destination addresses which fall within
an outbound IATU aperture range, they get unintentionally translated by
the IATU, causing the wrong address to be sent on the PCIe link.
This results in data corruption or IOMMU errors at the host if the
translated address is not mapped.

Set the DMA_BYPASS bit (bit 27) in PCIE_ATU_REGION_CTRL2 when programming
outbound IATU regions to ensure DMA transactions bypass IATU translation
and use their original addresses.

Signed-off-by: Sumit Kumar <sumit.kumar@oss.qualcomm.com>
---
pci: designware: Set DMA_BYPASS in outbound IATU to prevent HDMA
interception
---
 drivers/pci/controller/dwc/pcie-designware.c | 2 ++
 drivers/pci/controller/dwc/pcie-designware.h | 1 +
 2 files changed, 3 insertions(+)

diff --git a/drivers/pci/controller/dwc/pcie-designware.c b/drivers/pci/controller/dwc/pcie-designware.c
index 593388f29bdd48381cb04710f445042aaf2be29f..9297d0e607e3a1caaeb585b23742f9a29607b7f2 100644
--- a/drivers/pci/controller/dwc/pcie-designware.c
+++ b/drivers/pci/controller/dwc/pcie-designware.c
@@ -577,6 +577,8 @@ int dw_pcie_prog_outbound_atu(struct dw_pcie *pci,
 		/* The data-less messages only for now */
 		val |= PCIE_ATU_INHIBIT_PAYLOAD | atu->code;
 	}
+	if (dw_pcie_ver_is_ge(pci, 460A))
+		val |= PCIE_ATU_DMA_BYPASS;
 	dw_pcie_writel_atu_ob(pci, atu->index, PCIE_ATU_REGION_CTRL2, val);
 
 	/*
diff --git a/drivers/pci/controller/dwc/pcie-designware.h b/drivers/pci/controller/dwc/pcie-designware.h
index 0735ae94092404bc2976af67a58f6842cc5e5c50..668a5ba1c6f59aef1aaf15566b77a649bd282ce0 100644
--- a/drivers/pci/controller/dwc/pcie-designware.h
+++ b/drivers/pci/controller/dwc/pcie-designware.h
@@ -201,6 +201,7 @@
 #define PCIE_ATU_ENABLE			BIT(31)
 #define PCIE_ATU_BAR_MODE_ENABLE	BIT(30)
 #define PCIE_ATU_CFG_SHIFT_MODE_ENABLE	BIT(28)
+#define PCIE_ATU_DMA_BYPASS		BIT(27)
 #define PCIE_ATU_INHIBIT_PAYLOAD	BIT(22)
 #define PCIE_ATU_FUNC_NUM_MATCH_EN      BIT(19)
 #define PCIE_ATU_LOWER_BASE		0x008

---
base-commit: 45c13f3f9e3bb15fd89ff2864c6f627a3b4b4229
change-id: 20260826-dma_bypass-bbbf8a0c9af7

Best regards,
-- 
Sumit Kumar <sumit.kumar@oss.qualcomm.com>

Re: [PATCH] pci: designware: Set DMA_BYPASS bit in outbound IATU CTRL2 register

[Manivannan Sadhasivam]

On Wed, Aug 26, 2026 at 02:41:20PM +0530, Sumit Kumar wrote:
> Outbound IATU apertures are configured with local device-side addresses.
> When DMA engine transactions use destination addresses which fall within
> an outbound IATU aperture range, they get unintentionally translated by
> the IATU, causing the wrong address to be sent on the PCIe link.
> This results in data corruption or IOMMU errors at the host if the
> translated address is not mapped.
> 

Why are you using the same device address in both DMA and iATU mapping? This
sounds like a mapping problem that you should fix instead.

- Mani

-- 
மணிவண்ணன் சதாசிவம்

Re: [PATCH] pci: designware: Set DMA_BYPASS bit in outbound IATU CTRL2 register

[Krishna Chaitanya Chundru]

On 9/2/2026 7:37 PM, Manivannan Sadhasivam wrote:
> On Wed, Aug 26, 2026 at 02:41:20PM +0530, Sumit Kumar wrote:
>> Outbound IATU apertures are configured with local device-side addresses.
>> When DMA engine transactions use destination addresses which fall within
>> an outbound IATU aperture range, they get unintentionally translated by
>> the IATU, causing the wrong address to be sent on the PCIe link.
>> This results in data corruption or IOMMU errors at the host if the
>> translated address is not mapped.
>>
> Why are you using the same device address in both DMA and iATU mapping? This
> sounds like a mapping problem that you should fix instead.
issue happens, when host address(DMA destination address) matches with the
internal iova address programmed in iATU src address.
As we can cannot address in both,  we need to program iATU in DMA bypass mode,
so DMA transcations will not go through iATU window.

- Krishna Chaitanya.
>
> - Mani
>

Re: [PATCH] pci: designware: Set DMA_BYPASS bit in outbound IATU CTRL2 register

[Manivannan Sadhasivam]

On Wed, Sep 02, 2026 at 08:44:57PM +0530, Krishna Chaitanya Chundru wrote:
> 
> 
> On 9/2/2026 7:37 PM, Manivannan Sadhasivam wrote:
> > On Wed, Aug 26, 2026 at 02:41:20PM +0530, Sumit Kumar wrote:
> >> Outbound IATU apertures are configured with local device-side addresses.
> >> When DMA engine transactions use destination addresses which fall within
> >> an outbound IATU aperture range, they get unintentionally translated by
> >> the IATU, causing the wrong address to be sent on the PCIe link.
> >> This results in data corruption or IOMMU errors at the host if the
> >> translated address is not mapped.
> >>
> > Why are you using the same device address in both DMA and iATU mapping? This
> > sounds like a mapping problem that you should fix instead.
> issue happens, when host address(DMA destination address) matches with the
> internal iova address programmed in iATU src address.
> As we can cannot address in both,  we need to program iATU in DMA bypass mode,
> so DMA transcations will not go through iATU window.
> 

This needs to be explained clearly in the commit message with an example
matching the DWC terminologies such as 'Target Address Registers'.

- Mani

-- 
மணிவண்ணன் சதாசிவம்