PCI/ACS: Fix 'pci=config_acs=' parameter

Commit 47c8846a49ba ("PCI: Extend ACS configurability") introduced bugs
that fail to configure ACS ctrl to the value specified by the kernel
parameter. Essentially there are two bugs:

1) When ACS is configured for multiple PCI devices using 'config_acs'
   kernel parameter, it results into error "PCI: Can't parse ACS command
   line parameter". This is due to a bug that doesn't preserve the ACS
   mask, but instead overwrites the mask with value 0.

   For example, using 'config_acs' to configure ACS ctrl for multiple BDFs
   fails:

      Kernel command line: pci=config_acs=1111011@0020:02:00.0;101xxxx@0039:00:00.0 "dyndbg=file drivers/pci/pci.c +p"
      PCI: Can't parse ACS command line parameter
      pci 0020:02:00.0: ACS mask  = 0x007f
      pci 0020:02:00.0: ACS flags = 0x007b
      pci 0020:02:00.0: Configured ACS to 0x007b

   After this fix:

      Kernel command line: pci=config_acs=1111011@0020:02:00.0;101xxxx@0039:00:00.0 "dyndbg=file drivers/pci/pci.c +p"
      pci 0020:02:00.0: ACS mask  = 0x007f
      pci 0020:02:00.0: ACS flags = 0x007b
      pci 0020:02:00.0: ACS control = 0x005f
      pci 0020:02:00.0: ACS fw_ctrl = 0x0053
      pci 0020:02:00.0: Configured ACS to 0x007b
      pci 0039:00:00.0: ACS mask  = 0x0070
      pci 0039:00:00.0: ACS flags = 0x0050
      pci 0039:00:00.0: ACS control = 0x001d
      pci 0039:00:00.0: ACS fw_ctrl = 0x0000
      pci 0039:00:00.0: Configured ACS to 0x0050

2) In the bit manipulation logic, we copy the bit from the firmware
   settings when mask bit 0.

   For example, 'disable_acs_redir' fails to clear all three ACS P2P redir
   bits due to the wrong bit fiddling:

      Kernel command line: pci=disable_acs_redir=0020:02:00.0;0030:02:00.0;0039:00:00.0 "dyndbg=file drivers/pci/pci.c +p"
      pci 0020:02:00.0: ACS mask  = 0x002c
      pci 0020:02:00.0: ACS flags = 0xffd3
      pci 0020:02:00.0: Configured ACS to 0xfffb
      pci 0030:02:00.0: ACS mask  = 0x002c
      pci 0030:02:00.0: ACS flags = 0xffd3
      pci 0030:02:00.0: Configured ACS to 0xffdf
      pci 0039:00:00.0: ACS mask  = 0x002c
      pci 0039:00:00.0: ACS flags = 0xffd3
      pci 0039:00:00.0: Configured ACS to 0xffd3

   After this fix:

      Kernel command line: pci=disable_acs_redir=0020:02:00.0;0030:02:00.0;0039:00:00.0 "dyndbg=file drivers/pci/pci.c +p"
      pci 0020:02:00.0: ACS mask  = 0x002c
      pci 0020:02:00.0: ACS flags = 0xffd3
      pci 0020:02:00.0: ACS control = 0x007f
      pci 0020:02:00.0: ACS fw_ctrl = 0x007b
      pci 0020:02:00.0: Configured ACS to 0x0053
      pci 0030:02:00.0: ACS mask  = 0x002c
      pci 0030:02:00.0: ACS flags = 0xffd3
      pci 0030:02:00.0: ACS control = 0x005f
      pci 0030:02:00.0: ACS fw_ctrl = 0x005f
      pci 0030:02:00.0: Configured ACS to 0x0053
      pci 0039:00:00.0: ACS mask  = 0x002c
      pci 0039:00:00.0: ACS flags = 0xffd3
      pci 0039:00:00.0: ACS control = 0x001d
      pci 0039:00:00.0: ACS fw_ctrl = 0x0000
      pci 0039:00:00.0: Configured ACS to 0x0000

Link: https://lore.kernel.org/r/20250207030338.456887-1-tdave@nvidia.com
Fixes: 47c8846a49ba ("PCI: Extend ACS configurability")
Signed-off-by: Tushar Dave <tdave@nvidia.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>
Reviewed-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.intel.com>

1 files changed, 13 insertions, 5 deletions

diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
index 869d204a70a3..23609dd123f9 100644
--- a/drivers/pci/pci.c
+++ b/drivers/pci/pci.c
@@ -954,8 +954,10 @@ struct pci_acs {
 };
 
 static void __pci_config_acs(struct pci_dev *dev, struct pci_acs *caps,
-			     const char *p, u16 mask, u16 flags)
+			     const char *p, const u16 acs_mask, const u16 acs_flags)
 {
+	u16 flags = acs_flags;
+	u16 mask = acs_mask;
 	char *delimit;
 	int ret = 0;
 
@@ -963,7 +965,7 @@ static void __pci_config_acs(struct pci_dev *dev, struct pci_acs *caps,
 		return;
 
 	while (*p) {
-		if (!mask) {
+		if (!acs_mask) {
 			/* Check for ACS flags */
 			delimit = strstr(p, "@");
 			if (delimit) {
@@ -971,6 +973,8 @@ static void __pci_config_acs(struct pci_dev *dev, struct pci_acs *caps,
 				u32 shift = 0;
 
 				end = delimit - p - 1;
+				mask = 0;
+				flags = 0;
 
 				while (end > -1) {
 					if (*(p + end) == '0') {
@@ -1027,10 +1031,14 @@ static void __pci_config_acs(struct pci_dev *dev, struct pci_acs *caps,
 
 	pci_dbg(dev, "ACS mask  = %#06x\n", mask);
 	pci_dbg(dev, "ACS flags = %#06x\n", flags);
+	pci_dbg(dev, "ACS control = %#06x\n", caps->ctrl);
+	pci_dbg(dev, "ACS fw_ctrl = %#06x\n", caps->fw_ctrl);
 
-	/* If mask is 0 then we copy the bit from the firmware setting. */
-	caps->ctrl = (caps->ctrl & ~mask) | (caps->fw_ctrl & mask);
-	caps->ctrl |= flags;
+	/*
+	 * For mask bits that are 0, copy them from the firmware setting
+	 * and apply flags for all the mask bits that are 1.
+	 */
+	caps->ctrl = (caps->fw_ctrl & ~mask) | (flags & mask);
 
 	pci_info(dev, "Configured ACS to %#06x\n", caps->ctrl);
 }