Re: [PATCH v9 4/5] PCI: dwc: ep: Support BAR subrange inbound mapping via Address Match Mode iATU

[Niklas Cassel <cassel@kernel.org>]

On 22 January 2026 15:29:02 CET, Koichiro Den <den@valinux.co.jp> wrote:
>
>> To make sure that dw_pcie_ep_ib_atu_addr() cannot be called without already
>> having a BAR configured, to we perhaps want something like:
>
>Thanks for the review.
>Isn't the existing guard in dw_pcie_ep_ib_atu_addr sufficient?
>
>        [...]
>        base = dw_pcie_ep_read_bar_assigned(ep, func_no, bar, epf_bar->flags);
>        if (!base) {
>                dev_err(dev,
>                        "BAR%u not assigned, cannot set up sub-range mappings\n",
>                        bar);
>                return -EINVAL;
>        }
>

Well, for a driver that does not call dw_pcie_ep_reset_bar() in their .init() to disable all BARs that are enabled in the controller by default, the host side will assign an PCI address even if no EPF has called set_bar() on that BAR.

See e.g.
https://git.kernel.org/pub/scm/linux/kernel/git/pci/pci.git/commit/drivers/pci/controller/dwc/pcie-tegra194.c?h=controller/dwc&id=42f9c66a6d0cc45758dab77233c5460e1cf003df

There might be other EPC drivers that don't disable all BARs in their .init(), so I would say that simply checking if the BAR has an address is not sufficient to guarantee that an EPF driver has called set_bar().


I think the safest option is my second suggestion because then we know that we will only call
dw_pcie_ep_ib_atu_addr()

When:

1) If ep->epf_bar[bar] is set:
https://github.com/torvalds/linux/blob/v6.19-rc6/drivers/pci/controller/dwc/pcie-designware-ep.c#L363


2) All the other requirements to dynamically update a BAR is also met:

https://github.com/torvalds/linux/blob/v6.19-rc6/drivers/pci/controller/dwc/pcie-designware-ep.c#L368-L370



Kind regards,
Niklas