Re: [PATCH v2] PCI: dwc: Skip MEM outbound iATU setup for identity mappings

[Koichiro Den]

On Tue, Oct 20, 2026 at 10:37:35AM +0800, Xincheng Ji wrote:
> No outbound iATU translation is required when the parent-bus address
> matches the PCI address. This is a DesignWare controller property, not
> an UltraRISC-specific behavior.
> 
> Compare the addresses directly and skip MEM outbound iATU setup when
> they match. Remove bypass_ob_mem_iatu and the UltraRISC-specific setting.
> CFG and I/O accesses, as well as non-identity-mapped MEM ranges, still
> use outbound iATU windows.

Tested this on R-Car S4 (DWC PCIe 5.20a) in RP mode and did not observe any
issues.

Tested-by: Koichiro Den <den@xxxxxxxxxxxxx>

> 
> Fixes: 17b478b29cf1 ("PCI: dwc: Allow drivers to skip MEM outbound iATU setup")
> Fixes: 8da2b970ed4c ("PCI: ultrarisc: Skip MEM outbound iATU setup on DP1000")
> Signed-off-by: Xincheng Ji <jixincheng@xxxxxxxxxxxxx>
> ---
> This series follows up on the recently applied MEM outbound iATU support.
> 
> The DesignWare outbound no-match path does not translate addresses. Skip
> MEM outbound iATU programming whenever atu.parent_bus_addr matches
> atu.pci_addr, rather than relying on a driver-specific flag. CFG and I/O
> accesses, as well as non-identity-mapped MEM ranges, continue to use
> outbound iATU windows.
> 
> The UltraRISC DP1000 driver has removed the now-unneeded 
> bypass_ob_mem_iatu, and the general DesignWare PCIe host 
> code has also dropped bypass_ob_mem_iatu, directly comparing 
> the parent bus and PCI addresses before setting up the MEM 
> outbound iATU window
> ---
> Changes in v2:
> - Merge patch1 and patch2, because they depend on each other
> - Link to v1: https://patch.msgid.link/20261019-dw-pci-fix-v1-0-9b7860f919b9@xxxxxxxxxxxxx
> ---
>  drivers/pci/controller/dwc/pcie-designware-host.c | 17 +++++------------
>  drivers/pci/controller/dwc/pcie-designware.h      |  1 -
>  drivers/pci/controller/dwc/pcie-ultrarisc.c       |  6 ------
>  3 files changed, 5 insertions(+), 19 deletions(-)
> 
> diff --git a/drivers/pci/controller/dwc/pcie-designware-host.c b/drivers/pci/controller/dwc/pcie-designware-host.c
> index cf5ca281e91b..c593a1f1c2e0 100644
> --- a/drivers/pci/controller/dwc/pcie-designware-host.c
> +++ b/drivers/pci/controller/dwc/pcie-designware-host.c
> @@ -918,19 +918,12 @@ static int dw_pcie_iatu_setup(struct dw_pcie_rp *pp)
>  		atu.parent_bus_addr = entry->res->start - pci->parent_bus_offset;
>  		atu.pci_addr = entry->res->start - entry->offset;
>  
> -		if (pp->bypass_ob_mem_iatu) {
> -			/*
> -			 * The no-match pass-through path preserves the correct
> -			 * PCI address only for identity-mapped MEM ranges.
> -			 */
> -			if (atu.parent_bus_addr != atu.pci_addr) {
> -				dev_err(pci->dev,
> -					"Cannot bypass outbound iATU for non-identity MEM range %pr\n",
> -					entry->res);
> -				return -EINVAL;
> -			}
> +		/*
> +		 * No ATU translation is required when the parent-bus address matches
> +		 * the PCI address. This is a property of the DesignWare controller.
> +		 */
> +		if (atu.parent_bus_addr == atu.pci_addr)
>  			continue;
> -		}
>  
>  		/* Adjust iATU size if MSG TLP region was allocated before */
>  		if (pp->msg_res && pp->msg_res->parent == entry->res)
> diff --git a/drivers/pci/controller/dwc/pcie-designware.h b/drivers/pci/controller/dwc/pcie-designware.h
> index 799c05213ae3..128729fee607 100644
> --- a/drivers/pci/controller/dwc/pcie-designware.h
> +++ b/drivers/pci/controller/dwc/pcie-designware.h
> @@ -471,7 +471,6 @@ struct dw_pcie_rp {
>  	struct pci_config_window *cfg;
>  	bool			ecam_enabled;
>  	bool			native_ecam;
> -	bool			bypass_ob_mem_iatu;
>  	bool                    skip_l23_ready;
>  	bool			skip_pwrctrl_off;
>  	/* Set if the RC loses power during suspend */
> diff --git a/drivers/pci/controller/dwc/pcie-ultrarisc.c b/drivers/pci/controller/dwc/pcie-ultrarisc.c
> index 523f454c6c52..a0d328c0c09b 100644
> --- a/drivers/pci/controller/dwc/pcie-ultrarisc.c
> +++ b/drivers/pci/controller/dwc/pcie-ultrarisc.c
> @@ -154,12 +154,6 @@ static int ultrarisc_pcie_probe(struct platform_device *pdev)
>  
>  	pp = &pci->pp;
>  
> -	/*
> -	 * DP1000 routes MEM transactions without outbound iATU windows, which
> -	 * avoids the 16-window/4GB-per-window aperture limit.
> -	 */
> -	pp->bypass_ob_mem_iatu = true;
> -
>  	platform_set_drvdata(pdev, ultra);
>  
>  	ret = ultrarisc_pcie_init_clks(ultra);
> 
> ---
> base-commit: 0a2602de077462d3111eb9fd3da5b12a57fc6c93
> change-id: 20261015-dw-pci-fix-c8e51f83be02
> 
> Best regards,
> --  
> Xincheng Ji <jixincheng@xxxxxxxxxxxxx>
>