[PATCH 3/5] PCI: Add pcie_capability_user_read_{word,dword}()

[Matthew Wood <thepacketgeek@gmail.com>]

pcie_capability_read_word() and pcie_capability_read_dword() use the
kernel config accessors which don't check block_cfg_access, so they
can't be used for reads on behalf of userspace that should wait for a
reset (or other pci_cfg_access_lock() holder) to finish.

Add pcie_capability_user_read_word() and
pcie_capability_user_read_dword() helpers, which provide the same function
using the user config accessors.

These are for use within the PCI core, so they are declared in
drivers/pci/pci.h and not exported.

Signed-off-by: Matthew Wood <thepacketgeek@gmail.com>
Tested-by: Nikita Vetoshkin <nekto0n@meta.com>
---
 drivers/pci/access.c | 50 ++++++++++++++++++++++++++++++++++++++++++++
 drivers/pci/pci.h    |  2 ++
 2 files changed, 52 insertions(+)

diff --git a/drivers/pci/access.c b/drivers/pci/access.c
index 18a206bb2a94..ff5a16236758 100644
--- a/drivers/pci/access.c
+++ b/drivers/pci/access.c
@@ -490,6 +490,56 @@ int pcie_capability_read_dword(struct pci_dev *dev, int pos, u32 *val)
 }
 EXPORT_SYMBOL(pcie_capability_read_dword);
 
+/*
+ * Same as pcie_capability_read_{word,dword}(), but using the user config
+ * accessors.  Returns 0 on success, negative values indicate error.
+ */
+int pcie_capability_user_read_word(struct pci_dev *dev, int pos, u16 *val)
+{
+	int ret;
+
+	*val = 0;
+	if (pos & 1)
+		return -EINVAL;
+
+	if (pcie_capability_reg_implemented(dev, pos)) {
+		ret = pci_user_read_config_word(dev, pci_pcie_cap(dev) + pos,
+						val);
+		if (ret)
+			*val = 0;
+		return ret;
+	}
+
+	if (pci_is_pcie(dev) && pcie_downstream_port(dev) &&
+	    pos == PCI_EXP_SLTSTA)
+		*val = PCI_EXP_SLTSTA_PDS;
+
+	return 0;
+}
+
+int pcie_capability_user_read_dword(struct pci_dev *dev, int pos, u32 *val)
+{
+	int ret;
+
+	*val = 0;
+	if (pos & 3)
+		return -EINVAL;
+
+	if (pcie_capability_reg_implemented(dev, pos)) {
+		ret = pci_user_read_config_dword(dev, pci_pcie_cap(dev) + pos,
+						 val);
+		if (ret)
+			*val = 0;
+		return ret;
+	}
+
+	if (pci_is_pcie(dev) && pcie_downstream_port(dev) &&
+	    pos == PCI_EXP_SLTSTA)
+		*val = PCI_EXP_SLTSTA_PDS;
+
+	return 0;
+}
+
 int pcie_capability_write_word(struct pci_dev *dev, int pos, u16 val)
 {
 	if (pos & 1)
diff --git a/drivers/pci/pci.h b/drivers/pci/pci.h
index 77efa4c5c960..7c5a2ebc5706 100644
--- a/drivers/pci/pci.h
+++ b/drivers/pci/pci.h
@@ -128,6 +128,8 @@ extern struct mutex pci_rescan_remove_lock;
 bool pcie_cap_has_lnkctl(const struct pci_dev *dev);
 bool pcie_cap_has_lnkctl2(const struct pci_dev *dev);
 bool pcie_cap_has_rtctl(const struct pci_dev *dev);
+int pcie_capability_user_read_word(struct pci_dev *dev, int pos, u16 *val);
+int pcie_capability_user_read_dword(struct pci_dev *dev, int pos, u32 *val);
 
 /* Standard Capability finder */
 /**
-- 
2.53.0-Meta