linux-kernel - Re: [PATCH v9 2/5] PCI: endpoint: Add BAR subrange mapping support

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Message-ID: <aXHn3zuxxfBN1yps@ryzen>
Date: Thu, 22 Jan 2026 10:03:33 +0100
From: Niklas Cassel <cassel@...nel.org>
To: Koichiro Den <den@...inux.co.jp>
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Subject: Re: [PATCH v9 2/5] PCI: endpoint: Add BAR subrange mapping support

On Thu, Jan 22, 2026 at 05:49:06PM +0900, Koichiro Den wrote:
> Some endpoint platforms have only a small number of usable BARs. At the
> same time, EPF drivers (e.g. vNTB) may need multiple independent inbound
> regions (control/scratchpad, one or more memory windows, and optionally
> MSI or other feature-related regions). Subrange mapping allows these to
> share a single BAR without consuming additional BARs that may not be
> available, or forcing a fragile layout by aggressively packing into a
> single contiguous memory range.
> 
> Extend the PCI endpoint core to support mapping subranges within a BAR.
> Add an optional 'submap' field in struct pci_epf_bar so an endpoint
> function driver can request inbound mappings that fully cover the BAR.
> 
> Introduce a new EPC feature bit, subrange_mapping, and reject submap
> requests from pci_epc_set_bar() unless the controller advertises both
> subrange_mapping and dynamic_inbound_mapping features.
> 
> The submap array describes the complete BAR layout (no overlaps and no
> gaps are allowed to avoid exposing untranslated address ranges). This
> provides the generic infrastructure needed to map multiple logical
> regions into a single BAR at different offsets, without assuming a
> controller-specific inbound address translation mechanism.
> 
> Signed-off-by: Koichiro Den <den@...inux.co.jp>
> ---

Reviewed-by: Niklas Cassel <cassel@...nel.org>