PCI: endpoint: Allow EPF drivers to configure the size of Resizable BARs

PCI: endpoint: Allow EPF drivers to configure the size of Resizable BARs

A resizable BAR is different from a normal BAR in a few ways:

  - The minimum size of a resizable BAR is 1 MB.
  - Each BAR that is resizable has a Capability and Control register in
    the Resizable BAR Capability structure.

These registers contain the supported sizes and the currently selected
size of a resizable BAR.

The supported sizes is a bitmap of the supported sizes. The selected size
is a single value that is equal to one of the supported sizes.

A resizable BAR thus has to be configured differently than a
BAR_PROGRAMMABLE BAR, which usually sets the BAR size/mask in a vendor
specific way.

The PCI endpoint framework currently does not support resizable BARs.

Add a BAR type BAR_RESIZABLE, so that an EPC driver can support resizable
BARs properly.

Note that the pci_epc_set_bar() API takes a struct pci_epf_bar which tells
the EPC driver how it wants to configure the BAR.

struct pci_epf_bar only has a single size struct member.

This means that an EPC driver will only be able to set a single supported
size. This is perfectly fine, as we do not need the complexity of allowing
a host to change the size of the BAR. If someone ever wants to support
resizing a resizable BAR, the pci_epc_set_bar() API can be extended in the
future.

With these changes, we allow an EPF driver to configure the size of
Resizable BARs, rather than forcing them to a 1 MB size.

Signed-off-by: Niklas Cassel <cassel@kernel.org>
Reviewed-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
Link: https://lore.kernel.org/r/20250131182949.465530-10-cassel@kernel.org
Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
[kwilczynski: commit log]
Signed-off-by: Krzysztof Wilczyński <kwilczynski@kernel.org>