PCI: Cache ACS Capabilities register

The ACS Capability register is read-only. Cache it to allow quirks to
override it and to avoid re-reading it.

Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@oss.qualcomm.com>
[bhelgaas: commit log]
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Tested-by: Marek Szyprowski <m.szyprowski@samsung.com>
Tested-by: Naresh Kamboju <naresh.kamboju@linaro.org>
Link: https://patch.msgid.link/20260102-pci_acs-v3-2-72280b94d288@oss.qualcomm.com

Author: Mani-Sadhasivam

drivers/pci/pci.c

@@ -893,7 +893,6 @@ static const char *disable_acs_redir_param;
 static const char *config_acs_param;
 
 struct pci_acs {
-	u16 cap;
 	u16 ctrl;
 	u16 fw_ctrl;
 };
@@ -996,20 +995,20 @@ static void __pci_config_acs(struct pci_dev *dev, struct pci_acs *caps,
 static void pci_std_enable_acs(struct pci_dev *dev, struct pci_acs *caps)
 {
 	/* Source Validation */
-	caps->ctrl |= (caps->cap & PCI_ACS_SV);
+	caps->ctrl |= (dev->acs_capabilities & PCI_ACS_SV);
 
 	/* P2P Request Redirect */
-	caps->ctrl |= (caps->cap & PCI_ACS_RR);
+	caps->ctrl |= (dev->acs_capabilities & PCI_ACS_RR);
 
 	/* P2P Completion Redirect */
-	caps->ctrl |= (caps->cap & PCI_ACS_CR);
+	caps->ctrl |= (dev->acs_capabilities & PCI_ACS_CR);
 
 	/* Upstream Forwarding */
-	caps->ctrl |= (caps->cap & PCI_ACS_UF);
+	caps->ctrl |= (dev->acs_capabilities & PCI_ACS_UF);
 
 	/* Enable Translation Blocking for external devices and noats */
 	if (pci_ats_disabled() || dev->external_facing || dev->untrusted)
-		caps->ctrl |= (caps->cap & PCI_ACS_TB);
+		caps->ctrl |= (dev->acs_capabilities & PCI_ACS_TB);
 }
 
 /**
@@ -1032,7 +1031,6 @@ void pci_enable_acs(struct pci_dev *dev)
 	if (!pos)
 		return;
 
-	pci_read_config_word(dev, pos + PCI_ACS_CAP, &caps.cap);
 	pci_read_config_word(dev, pos + PCI_ACS_CTRL, &caps.ctrl);
 	caps.fw_ctrl = caps.ctrl;
 
@@ -3515,7 +3513,7 @@ void pci_configure_ari(struct pci_dev *dev)
 static bool pci_acs_flags_enabled(struct pci_dev *pdev, u16 acs_flags)
 {
 	int pos;
-	u16 cap, ctrl;
+	u16 ctrl;
 
 	pos = pdev->acs_cap;
 	if (!pos)
@@ -3526,8 +3524,7 @@ static bool pci_acs_flags_enabled(struct pci_dev *pdev, u16 acs_flags)
 	 * or only required if controllable.  Features missing from the
 	 * capability field can therefore be assumed as hard-wired enabled.
 	 */
-	pci_read_config_word(pdev, pos + PCI_ACS_CAP, &cap);
-	acs_flags &= (cap | PCI_ACS_EC);
+	acs_flags &= (pdev->acs_capabilities | PCI_ACS_EC);
 
 	pci_read_config_word(pdev, pos + PCI_ACS_CTRL, &ctrl);
 	return (ctrl & acs_flags) == acs_flags;
@@ -3648,7 +3645,14 @@ bool pci_acs_path_enabled(struct pci_dev *start,
  */
 void pci_acs_init(struct pci_dev *dev)
 {
+	int pos;
+
 	dev->acs_cap = pci_find_ext_capability(dev, PCI_EXT_CAP_ID_ACS);
+	pos = dev->acs_cap;
+	if (!pos)
+		return;
+
+	pci_read_config_word(dev, pos + PCI_ACS_CAP, &dev->acs_capabilities);
 }
 
 /**

include/linux/pci.h

@@ -558,6 +558,7 @@ struct pci_dev {
 	struct pci_tsm *tsm;		/* TSM operation state */
 #endif
 	u16		acs_cap;	/* ACS Capability offset */
+	u16		acs_capabilities; /* ACS Capabilities */
 	u8		supported_speeds; /* Supported Link Speeds Vector */
 	phys_addr_t	rom;		/* Physical address if not from BAR */
 	size_t		romlen;		/* Length if not from BAR */