[PATCH 03/10] PCI: Factor out bridge window probing from pci_read_bridge_windows()

[David Matlack <dmatlack@google.com>]

Move the code that determines which windows a bridge implements, which
requires temporarily writing to the window registers, out of
pci_read_bridge_windows() and into a new helper,
pci_probe_bridge_windows(). Probe all windows before reading any of
them.

A subsequent commit will obtain which windows are implemented by bridges
preserved across Live Update from the previous kernel instead of probing
them, since probing can temporarily disable windows.

No functional change intended.

Assisted-by: LLM
Signed-off-by: David Matlack <dmatlack@google.com>
---
 drivers/pci/probe.c | 44 ++++++++++++++++++++++++++++----------------
 1 file changed, 28 insertions(+), 16 deletions(-)

diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c
index 3cb2e481eddf..473e4389ffae 100644
--- a/drivers/pci/probe.c
+++ b/drivers/pci/probe.c
@@ -520,19 +520,14 @@ static void pci_read_bridge_mmio_pref(struct pci_dev *dev, struct resource *res,
 	}
 }
 
-static void pci_read_bridge_windows(struct pci_dev *bridge)
+/*
+ * Determine which windows @bridge implements. This requires temporarily
+ * writing to the window registers of windows that read as zero.
+ */
+static void pci_probe_bridge_windows(struct pci_dev *bridge)
 {
-	u32 buses;
 	u16 io;
 	u32 pmem, tmp;
-	struct resource res;
-
-	pci_read_config_dword(bridge, PCI_PRIMARY_BUS, &buses);
-	res.flags = IORESOURCE_BUS;
-	res.start = FIELD_GET(PCI_SECONDARY_BUS_MASK, buses);
-	res.end = FIELD_GET(PCI_SUBORDINATE_BUS_MASK, buses);
-	pci_info(bridge, "PCI bridge to %pR%s\n", &res,
-		 bridge->transparent ? " (subtractive decode)" : "");
 
 	pci_read_config_word(bridge, PCI_IO_BASE, &io);
 	if (!io) {
@@ -540,12 +535,8 @@ static void pci_read_bridge_windows(struct pci_dev *bridge)
 		pci_read_config_word(bridge, PCI_IO_BASE, &io);
 		pci_write_config_word(bridge, PCI_IO_BASE, 0x0);
 	}
-	if (io) {
+	if (io)
 		bridge->io_window = 1;
-		pci_read_bridge_io(bridge, &res, true);
-	}
-
-	pci_read_bridge_mmio(bridge, &res, true);
 
 	/*
 	 * DECchip 21050 pass 2 errata: the bridge may miss an address
@@ -582,8 +573,29 @@ static void pci_read_bridge_windows(struct pci_dev *bridge)
 		if (tmp)
 			bridge->pref_64_window = 1;
 	}
+}
+
+static void pci_read_bridge_windows(struct pci_dev *bridge)
+{
+	u32 buses;
+	struct resource res;
+
+	pci_read_config_dword(bridge, PCI_PRIMARY_BUS, &buses);
+	res.flags = IORESOURCE_BUS;
+	res.start = FIELD_GET(PCI_SECONDARY_BUS_MASK, buses);
+	res.end = FIELD_GET(PCI_SUBORDINATE_BUS_MASK, buses);
+	pci_info(bridge, "PCI bridge to %pR%s\n", &res,
+		 bridge->transparent ? " (subtractive decode)" : "");
+
+	pci_probe_bridge_windows(bridge);
+
+	if (bridge->io_window)
+		pci_read_bridge_io(bridge, &res, true);
+
+	pci_read_bridge_mmio(bridge, &res, true);
 
-	pci_read_bridge_mmio_pref(bridge, &res, true);
+	if (bridge->pref_window)
+		pci_read_bridge_mmio_pref(bridge, &res, true);
 }
 
 void pci_read_bridge_bases(struct pci_bus *child)
-- 
2.56.0.212.g129ede20d9-goog