Currently, __resource_resize_store() uses sysfs_remove_groups()
and sysfs_create_groups() on pci_dev_resource_attr_groups to
tear down and recreate the resourceN files after a BAR resize,
so the updated BAR sizes are visible in sysfs.

The resourceN files only exist on platforms that define
HAVE_PCI_MMAP or ARCH_GENERIC_PCI_MMAP_RESOURCE.  On platforms
that define neither, pci_dev_resource_attr_groups is NULL and
the sysfs_remove_groups() and sysfs_create_groups() calls in
__resource_resize_store() become no-ops.

Resizable BAR (ReBAR) is a PCI Express extended capability
(PCI_EXT_CAP_ID_REBAR) that requires PCIe extended config
space.  Every PCIe-capable architecture defines HAVE_PCI_MMAP
or ARCH_GENERIC_PCI_MMAP_RESOURCE (via arch headers or the
asm-generic/pci.h fallback).  Architectures without either
only support conventional PCI and cannot have any ReBAR-capable
devices.

Thus, move the resize show and store helpers, the per-BAR attribute
definitions, and the attribute group behind the existing #ifdef
HAVE_PCI_MMAP || ARCH_GENERIC_PCI_MMAP_RESOURCE guard, and fold the
group reference in pci_dev_groups[] into the existing #if block.

Tested-by: Shivaprasad G Bhat <redacted>
Signed-off-by: Krzysztof Wilczyński <kwilczynski@kernel.org>
---
 drivers/pci/pci-sysfs.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/drivers/pci/pci-sysfs.c b/drivers/pci/pci-sysfs.c
index dd87b83ba3a9..4216ed520d41 100644
--- a/drivers/pci/pci-sysfs.c
+++ b/drivers/pci/pci-sysfs.c

@@ -1652,6 +1652,7 @@ static const struct attribute_group pci_dev_reset_method_attr_group = {
 	.is_visible = pci_dev_reset_attr_is_visible,
 };
 
+#if defined(HAVE_PCI_MMAP) || defined(ARCH_GENERIC_PCI_MMAP_RESOURCE)
 static ssize_t __resource_resize_show(struct device *dev, int n, char *buf)
 {
 	struct pci_dev *pdev = to_pci_dev(dev);

@@ -1766,6 +1767,7 @@ static const struct attribute_group pci_dev_resource_resize_attr_group = {
 	.attrs = resource_resize_attrs,
 	.is_visible = resource_resize_attr_is_visible,
 };
+#endif
 
 static struct attribute *pci_dev_dev_attrs[] = {
 	&dev_attr_boot_vga.attr,

@@ -1840,8 +1842,8 @@ const struct attribute_group *pci_dev_groups[] = {
 	&pci_dev_resource_io_attr_group,
 	&pci_dev_resource_uc_attr_group,
 	&pci_dev_resource_wc_attr_group,
-#endif
 	&pci_dev_resource_resize_attr_group,
+#endif
 	&pci_dev_config_attr_group,
 	&pci_dev_rom_attr_group,
 	&pci_dev_reset_attr_group,

-- 
2.54.0