PCI: Add pci_rebar_bytes_to_size()

Users of pci_resize_resource() need a way to calculate BAR size
from desired bytes. Add a helper function and export it so that
modular drivers can use it.
Signed-off-by: Darren Salt <devspam@moreofthesa.me.uk>
Signed-off-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Nirmoy Das <nirmoy.das@amd.com>
Acked-by: Bjorn Helgaas <bhelgaas@google.com>
Link: https://patchwork.kernel.org/project/dri-devel/patch/20210107175017.15893-3-nirmoy.das@amd.com

drivers/pci/pci.c

@@ -1644,7 +1644,7 @@ static void pci_restore_rebar_state(struct pci_dev *pdev)
 		pci_read_config_dword(pdev, pos + PCI_REBAR_CTRL, &ctrl);
 		bar_idx = ctrl & PCI_REBAR_CTRL_BAR_IDX;
 		res = pdev->resource + bar_idx;
-		size = ilog2(resource_size(res)) - 20;
+		size = pci_rebar_bytes_to_size(resource_size(res));
 		ctrl &= ~PCI_REBAR_CTRL_BAR_SIZE;
 		ctrl |= size << PCI_REBAR_CTRL_BAR_SHIFT;
 		pci_write_config_dword(pdev, pos + PCI_REBAR_CTRL, ctrl);

include/linux/pci.h

@@ -1232,6 +1232,14 @@ void pci_update_resource(struct pci_dev *dev, int resno);
 int __must_check pci_assign_resource(struct pci_dev *dev, int i);
 int __must_check pci_reassign_resource(struct pci_dev *dev, int i, resource_size_t add_size, resource_size_t align);
 void pci_release_resource(struct pci_dev *dev, int resno);
+static inline int pci_rebar_bytes_to_size(u64 bytes)
+{
+	bytes = roundup_pow_of_two(bytes);
+
+	/* Return BAR size as defined in the resizable BAR specification */
+	return max(ilog2(bytes), 20) - 20;
+}
+
 u32 pci_rebar_get_possible_sizes(struct pci_dev *pdev, int bar);
 int __must_check pci_resize_resource(struct pci_dev *dev, int i, int size);
 int pci_select_bars(struct pci_dev *dev, unsigned long flags);