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

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

The DWC databook specifies three different BARn_SIZING_SCHEME_N as:

  - Fixed Mask (0)
  - Programmable Mask (1)
  - Resizable BAR (2)

Each of these sizing schemes have different instructions for how to
initialize the BAR.

The DWC driver currently does not support resizable BARs.

Instead, in order to somewhat support resizable BARs, the DWC EP driver
currently has an ugly hack that force sets a resizable BAR to 1 MB, if
such a BAR is detected.

Additionally, this hack only works if the DWC glue driver also has lied
in their EPC features, and claimed that the resizable BAR is a 1 MB fixed
size BAR.

This is unintuitive (as you somehow need to know that you need to lie in
your EPC features), but other than that it is overly restrictive, since a
resizable BAR is capable of supporting sizes different than 1 MB.

Add proper support for resizable BARs in the DWC EP driver.

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.

This means that an EPC driver does not need to lie in EPC features, and an
EPF driver will be able to set an arbitrary size (not be forced to a 1 MB
size), just like BAR_PROGRAMMABLE.

Signed-off-by: Niklas Cassel <cassel@kernel.org>
Reviewed-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
Link: https://lore.kernel.org/r/20250131182949.465530-13-cassel@kernel.org
Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
[kwilczynski: commit log]
Signed-off-by: Krzysztof Wilczyński <kwilczynski@kernel.org>