PCI/sysfs: Add __weak pci_legacy_has_sparse() helper

Currently, Alpha's sparse/dense legacy attribute handling is done via
pci_adjust_legacy_attr(), which updates dynamically allocated attributes at
runtime.  The upcoming conversion to static attributes needs a way to
determine sparse support at visibility check time.

Add a __weak pci_legacy_has_sparse() that returns false by default.  Alpha
overrides it to check has_sparse() on the bus host controller.

Signed-off-by: Krzysztof Wilczyński <kwilczynski@kernel.org>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Tested-by: Shivaprasad G Bhat <sbhat@linux.ibm.com>
Link: https://patch.msgid.link/20260508043543.217179-22-kwilczynski@kernel.org

arch/alpha/include/asm/pci.h

@@ -86,6 +86,8 @@ extern int pci_mmap_legacy_page_range(struct pci_bus *bus,
 				      enum pci_mmap_state mmap_state);
 extern void pci_adjust_legacy_attr(struct pci_bus *bus,
 				   enum pci_mmap_state mmap_type);
+extern bool pci_legacy_has_sparse(struct pci_bus *bus,
+				  enum pci_mmap_state type);
 #define HAVE_PCI_LEGACY	1
 
 extern const struct attribute_group pci_dev_resource_attr_group;

arch/alpha/kernel/pci-sysfs.c

@@ -184,6 +184,13 @@ int pci_mmap_legacy_page_range(struct pci_bus *bus, struct vm_area_struct *vma,
 	return hose_mmap_page_range(hose, vma, mmap_type, sparse);
 }
 
+bool pci_legacy_has_sparse(struct pci_bus *bus, enum pci_mmap_state type)
+{
+	struct pci_controller *hose = bus->sysdata;
+
+	return has_sparse(hose, type);
+}
+
 /**
  * pci_adjust_legacy_attr - adjustment of legacy file attributes
  * @bus: bus to create files under

drivers/pci/pci-sysfs.c

@@ -983,6 +983,12 @@ static int pci_mmap_legacy_io(struct file *filp, struct kobject *kobj,
 	return pci_mmap_legacy_page_range(bus, vma, pci_mmap_io);
 }
 
+bool __weak pci_legacy_has_sparse(struct pci_bus *bus,
+				  enum pci_mmap_state type)
+{
+	return false;
+}
+
 /**
  * pci_adjust_legacy_attr - adjustment of legacy file attributes
  * @b: bus to create files under

drivers/pci/pci.h

@@ -392,6 +392,10 @@ static inline int pci_no_d1d2(struct pci_dev *dev)
 
 }
 
+#ifdef HAVE_PCI_LEGACY
+bool pci_legacy_has_sparse(struct pci_bus *bus, enum pci_mmap_state type);
+#endif
+
 #ifdef CONFIG_SYSFS
 extern const struct attribute_group *pci_dev_groups[];
 extern const struct attribute_group *pci_dev_attr_groups[];