PCI: iproc: Allow outbound configuration for 32-bit I/O region

The IProc host controller has I/O memory windows allocated in
the AXI memory map that can be used to address PCI I/O memory
space.

Mapping from AXI memory windows to PCI outbound memory windows is
carried out in the host controller through OARR/OMAP registers pairs
that permit to define power of two region size AXI<->PCI mappings, the
smallest of which is 128MB.

Current code enables AXI memory window to PCI outbound memory window
mapping only for AXI windows matching one of the OARR/OMAP window sizes,
that are SoC dependent and the smallest of which is 128MB.

Some SoCs implementing the IProc host controller have a 32-bit AXI
memory window into PCI I/O memory space, eg:

    Base address | Size
-----------------------------
(1) 0x42000000   | 0x2000000
(2) 0x400000000  | 0x80000000

but its size (32MB - (1) above) is smaller than the smallest AXI<->PCI
region size provided by OARR (128MB), so the current driver rejects
mappings for the 32-bit region making the IProc host controller driver
unusable on 32-bit systems.

However, there is no reason why the 32-bit I/O memory window cannot be
enabled by mapping it through an OARR/OMAP region bigger in size (ie
32-bit AXI window size is 32MB but can be mapped using a 128MB OARR/OMAP
region).

Allow outbound window configuration of I/O memory windows that
are smaller in size than the host controller OARR/OMAP region, so
that the 32-bit AXI memory window can actually be enabled,
making the IProc host controller operational on 32-bit systems.

Link: https://lore.kernel.org/linux-pci/1551415936-30174-3-git-send-email-srinath.mannam@broadcom.com/Signed-off-by: Srinath Mannam <srinath.mannam@broadcom.com>
Signed-off-by: Abhishek Shah <abhishek.shah@broadcom.com>
Signed-off-by: Ray Jui <ray.jui@broadcom.com>
[lorenzo.pieralisi@arm.com: rewrote the commit log]
Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Acked-by: Scott Branden <scott.branden@broadcom.com>

drivers/pci/controller/pcie-iproc.c

@@ -955,8 +955,25 @@ static int iproc_pcie_setup_ob(struct iproc_pcie *pcie, u64 axi_addr,
 			resource_size_t window_size =
 				ob_map->window_sizes[size_idx] * SZ_1M;
 
-			if (size < window_size)
-				continue;
+			/*
+			 * Keep iterating until we reach the last window and
+			 * with the minimal window size at index zero. In this
+			 * case, we take a compromise by mapping it using the
+			 * minimum window size that can be supported
+			 */
+			if (size < window_size) {
+				if (size_idx > 0 || window_idx > 0)
+					continue;
+
+				/*
+				 * For the corner case of reaching the minimal
+				 * window size that can be supported on the
+				 * last window
+				 */
+				axi_addr = ALIGN_DOWN(axi_addr, window_size);
+				pci_addr = ALIGN_DOWN(pci_addr, window_size);
+				size = window_size;
+			}
 
 			if (!IS_ALIGNED(axi_addr, window_size) ||
 			    !IS_ALIGNED(pci_addr, window_size)) {