Re: [PATCH 1/2] PCI: dwc: Fix ECAM enablement when used with vendor drivers

[Ron Economos <re@w6rz.net>]

On 10/17/25 04:40, Krishna Chaitanya Chundru wrote:
> When the vendor configuration space is 256MB aligned, the DesignWare
> PCIe host driver enables ECAM access and sets the DBI base to the start
> of the config space. This causes vendor drivers to incorrectly program
> iATU regions, as they rely on the DBI address for internal accesses.
>
> To fix this, avoid overwriting the DBI base when ECAM is enabled.
> Instead, introduce a custom ECAM PCI ops implementation that accesses
> the DBI region directly for bus 0 and uses ECAM for other buses.
>
> Fixes: f6fd357f7afb ("PCI: dwc: Prepare the driver for enabling ECAM mechanism using iATU 'CFG Shift Feature'")
> Reported-by: Ron Economos <re@w6rz.net>
> Closes: https://lore.kernel.org/all/eac81c57-1164-4d74-a1b4-6f353c577731@w6rz.net/
> Suggested-by: Manivannan Sadhasivam <mani@kernel.org>
> Signed-off-by: Krishna Chaitanya Chundru <krishna.chundru@oss.qualcomm.com>
> ---
>   drivers/pci/controller/dwc/pcie-designware-host.c | 28 +++++++++++++++++++----
>   1 file changed, 24 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/pci/controller/dwc/pcie-designware-host.c b/drivers/pci/controller/dwc/pcie-designware-host.c
> index 20c9333bcb1c4812e2fd96047a49944574df1e6f..e92513c5bda51bde3a7157033ddbd73afa370d78 100644
> --- a/drivers/pci/controller/dwc/pcie-designware-host.c
> +++ b/drivers/pci/controller/dwc/pcie-designware-host.c
> @@ -23,6 +23,7 @@
>   #include "pcie-designware.h"
>   
>   static struct pci_ops dw_pcie_ops;
> +static struct pci_ops dw_pcie_ecam_ops;
>   static struct pci_ops dw_child_pcie_ops;
>   
>   #define DW_PCIE_MSI_FLAGS_REQUIRED (MSI_FLAG_USE_DEF_DOM_OPS		| \
> @@ -471,9 +472,6 @@ static int dw_pcie_create_ecam_window(struct dw_pcie_rp *pp, struct resource *re
>   	if (IS_ERR(pp->cfg))
>   		return PTR_ERR(pp->cfg);
>   
> -	pci->dbi_base = pp->cfg->win;
> -	pci->dbi_phys_addr = res->start;
> -
>   	return 0;
>   }
>   
> @@ -529,7 +527,7 @@ static int dw_pcie_host_get_resources(struct dw_pcie_rp *pp)
>   		if (ret)
>   			return ret;
>   
> -		pp->bridge->ops = (struct pci_ops *)&pci_generic_ecam_ops.pci_ops;
> +		pp->bridge->ops = &dw_pcie_ecam_ops;
>   		pp->bridge->sysdata = pp->cfg;
>   		pp->cfg->priv = pp;
>   	} else {
> @@ -842,12 +840,34 @@ void __iomem *dw_pcie_own_conf_map_bus(struct pci_bus *bus, unsigned int devfn,
>   }
>   EXPORT_SYMBOL_GPL(dw_pcie_own_conf_map_bus);
>   
> +static void __iomem *dw_pcie_ecam_conf_map_bus(struct pci_bus *bus, unsigned int devfn, int where)
> +{
> +	struct pci_config_window *cfg = bus->sysdata;
> +	struct dw_pcie_rp *pp = cfg->priv;
> +	struct dw_pcie *pci = to_dw_pcie_from_pp(pp);
> +	unsigned int busn = bus->number;
> +
> +	if (busn > 0)
> +		return pci_ecam_map_bus(bus, devfn, where);
> +
> +	if (PCI_SLOT(devfn) > 0)
> +		return NULL;
> +
> +	return pci->dbi_base + where;
> +}
> +
>   static struct pci_ops dw_pcie_ops = {
>   	.map_bus = dw_pcie_own_conf_map_bus,
>   	.read = pci_generic_config_read,
>   	.write = pci_generic_config_write,
>   };
>   
> +static struct pci_ops dw_pcie_ecam_ops = {
> +	.map_bus = dw_pcie_ecam_conf_map_bus,
> +	.read = pci_generic_config_read,
> +	.write = pci_generic_config_write,
> +};
> +
>   static int dw_pcie_iatu_setup(struct dw_pcie_rp *pp)
>   {
>   	struct dw_pcie *pci = to_dw_pcie_from_pp(pp);
>
Works good on the SiFive FU740 controller.

Tested-by: Ron Economos <re@w6rz.net>