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* [PATCH RFC] platform/x86: p2sb: Allow p2sb_bar() calls during PCI device probe
@ 2023-12-01 10:47 Shin'ichiro Kawasaki
  2023-12-04 14:10 ` Hans de Goede
  0 siblings, 1 reply; 2+ messages in thread
From: Shin'ichiro Kawasaki @ 2023-12-01 10:47 UTC (permalink / raw)
  To: platform-driver-x86
  Cc: Hans de Goede, Ilpo Järvinen, Andy Shevchenko, Lukas Wunner,
	linux-pci, linux-i2c, Shin'ichiro Kawasaki

p2sb_bar() unhides P2SB device to get resources from the device. It
guards the operation by locking pci_rescan_remove_lock so that parallel
rescans do not find the P2SB device. However, this lock causes deadlock
when PCI bus rescan is triggered by /sys/bus/pci/rescan. The rescan
locks pci_rescan_remove_lock and probes PCI devices. When PCI devices
call p2sb_bar() during probe, it locks pci_rescan_remove_lock again.
Hence the deadlock.

To avoid the deadlock, do not lock pci_rescan_remove_lock in p2sb_bar().
Instead, do the lock at fs_initcall. Introduce p2sb_cache_resources()
for fs_initcall which gets and caches the P2SB resources. At p2sb_bar(),
refer the cache and return to the caller.

Link: https://lore.kernel.org/linux-pci/6xb24fjmptxxn5js2fjrrddjae6twex5bjaftwqsuawuqqqydx@7cl3uik5ef6j/
Suggested-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Shin'ichiro Kawasaki <shinichiro.kawasaki@wdc.com>
---
This patch reflects discussions held at the Link tag. I confirmed this patch
fixes the problem using a system with i2c_i801 device, building i2c_i801
module as both built-in and loadable. Reviews will be appreicated.

 drivers/platform/x86/p2sb.c | 125 +++++++++++++++++++++++++-----------
 1 file changed, 87 insertions(+), 38 deletions(-)

diff --git a/drivers/platform/x86/p2sb.c b/drivers/platform/x86/p2sb.c
index 1cf2471d54dd..97e9b44f5f1a 100644
--- a/drivers/platform/x86/p2sb.c
+++ b/drivers/platform/x86/p2sb.c
@@ -26,6 +26,16 @@ static const struct x86_cpu_id p2sb_cpu_ids[] = {
 	{}
 };
 
+/* Cache BAR0 of P2SB device from function 0 ot 7 */
+#define NR_P2SB_RES_CACHE 8
+
+struct p2sb_res_cache {
+	u32 bus_dev_id;
+	struct resource res;
+};
+
+static struct p2sb_res_cache p2sb_resources[NR_P2SB_RES_CACHE];
+
 static int p2sb_get_devfn(unsigned int *devfn)
 {
 	unsigned int fn = P2SB_DEVFN_DEFAULT;
@@ -39,8 +49,13 @@ static int p2sb_get_devfn(unsigned int *devfn)
 	return 0;
 }
 
+static bool p2sb_invalid_resource(struct resource *res)
+{
+	return res->flags == 0;
+}
+
 /* Copy resource from the first BAR of the device in question */
-static int p2sb_read_bar0(struct pci_dev *pdev, struct resource *mem)
+static void p2sb_read_bar0(struct pci_dev *pdev, struct resource *mem)
 {
 	struct resource *bar0 = &pdev->resource[0];
 
@@ -56,48 +71,29 @@ static int p2sb_read_bar0(struct pci_dev *pdev, struct resource *mem)
 	mem->end = bar0->end;
 	mem->flags = bar0->flags;
 	mem->desc = bar0->desc;
-
-	return 0;
 }
 
-static int p2sb_scan_and_read(struct pci_bus *bus, unsigned int devfn, struct resource *mem)
+static int p2sb_scan_and_cache(struct pci_bus *bus, unsigned int devfn)
 {
 	struct pci_dev *pdev;
 	int ret;
+	struct p2sb_res_cache *cache = &p2sb_resources[PCI_FUNC(devfn)];
 
 	pdev = pci_scan_single_device(bus, devfn);
-	if (!pdev)
+	if (!pdev || p2sb_invalid_resource(&pdev->resource[0]))
 		return -ENODEV;
 
-	ret = p2sb_read_bar0(pdev, mem);
+	p2sb_read_bar0(pdev, &cache->res);
+	cache->bus_dev_id = bus->dev.id;
 
 	pci_stop_and_remove_bus_device(pdev);
 	return ret;
 }
 
-/**
- * p2sb_bar - Get Primary to Sideband (P2SB) bridge device BAR
- * @bus: PCI bus to communicate with
- * @devfn: PCI slot and function to communicate with
- * @mem: memory resource to be filled in
- *
- * The BIOS prevents the P2SB device from being enumerated by the PCI
- * subsystem, so we need to unhide and hide it back to lookup the BAR.
- *
- * if @bus is NULL, the bus 0 in domain 0 will be used.
- * If @devfn is 0, it will be replaced by devfn of the P2SB device.
- *
- * Caller must provide a valid pointer to @mem.
- *
- * Locking is handled by pci_rescan_remove_lock mutex.
- *
- * Return:
- * 0 on success or appropriate errno value on error.
- */
-int p2sb_bar(struct pci_bus *bus, unsigned int devfn, struct resource *mem)
+static int p2sb_cache_resources(void)
 {
-	struct pci_dev *pdev_p2sb;
-	unsigned int devfn_p2sb;
+	struct pci_bus *bus;
+	unsigned int devfn_p2sb, slot_p2sb, fn;
 	u32 value = P2SBC_HIDE;
 	int ret;
 
@@ -106,8 +102,8 @@ int p2sb_bar(struct pci_bus *bus, unsigned int devfn, struct resource *mem)
 	if (ret)
 		return ret;
 
-	/* if @bus is NULL, use bus 0 in domain 0 */
-	bus = bus ?: pci_find_bus(0, 0);
+	/* Assume P2SB is on the bus 0 in domain 0 */
+	bus = pci_find_bus(0, 0);
 
 	/*
 	 * Prevent concurrent PCI bus scan from seeing the P2SB device and
@@ -115,18 +111,31 @@ int p2sb_bar(struct pci_bus *bus, unsigned int devfn, struct resource *mem)
 	 */
 	pci_lock_rescan_remove();
 
-	/* Unhide the P2SB device, if needed */
+	/*
+	 * The BIOS prevents the P2SB device from being enumerated by the PCI
+	 * subsystem, so we need to unhide and hide it back to lookup the BAR.
+	 * Unhide the P2SB device here, if needed.
+	 */
 	pci_bus_read_config_dword(bus, devfn_p2sb, P2SBC, &value);
 	if (value & P2SBC_HIDE)
 		pci_bus_write_config_dword(bus, devfn_p2sb, P2SBC, 0);
 
-	pdev_p2sb = pci_scan_single_device(bus, devfn_p2sb);
-	if (devfn)
-		ret = p2sb_scan_and_read(bus, devfn, mem);
-	else
-		ret = p2sb_read_bar0(pdev_p2sb, mem);
-	pci_stop_and_remove_bus_device(pdev_p2sb);
+	/* Scan the P2SB device and cache its BAR0 */
+	ret = p2sb_scan_and_cache(bus, devfn_p2sb);
+	if (ret)
+		goto out;
 
+	/*
+	 * When function number of the P2SB device is zero, scan other function
+	 * numbers. If devices are available, cache their BAR0.
+	 */
+	if (!PCI_FUNC(devfn_p2sb)) {
+		slot_p2sb = PCI_SLOT(devfn_p2sb);
+		for (fn = 1; fn < 8; fn++)
+			p2sb_scan_and_cache(bus, PCI_DEVFN(slot_p2sb, fn));
+	}
+
+out:
 	/* Hide the P2SB device, if it was hidden */
 	if (value & P2SBC_HIDE)
 		pci_bus_write_config_dword(bus, devfn_p2sb, P2SBC, P2SBC_HIDE);
@@ -136,9 +145,49 @@ int p2sb_bar(struct pci_bus *bus, unsigned int devfn, struct resource *mem)
 	if (ret)
 		return ret;
 
-	if (mem->flags == 0)
+	return 0;
+}
+
+/**
+ * p2sb_bar - Get Primary to Sideband (P2SB) bridge device BAR
+ * @bus: PCI bus to communicate with
+ * @devfn: PCI slot and function to communicate with
+ * @mem: memory resource to be filled in
+ *
+ * if @bus is NULL, the bus 0 in domain 0 will be used.
+ * If @devfn is 0, it will be replaced by devfn of the P2SB device.
+ *
+ * Caller must provide a valid pointer to @mem.
+ *
+ * Return:
+ * 0 on success or appropriate errno value on error.
+ */
+int p2sb_bar(struct pci_bus *bus, unsigned int devfn, struct resource *mem)
+{
+	int ret;
+	struct p2sb_res_cache *cache;
+
+	bus = bus ? bus : pci_find_bus(0, 0);
+
+	if (!devfn) {
+		ret = p2sb_get_devfn(&devfn);
+		if (ret)
+			return ret;
+	}
+
+	cache = &p2sb_resources[PCI_FUNC(devfn)];
+	if (p2sb_invalid_resource(&cache->res) ||
+	    cache->bus_dev_id != bus->dev.id)
 		return -ENODEV;
 
+	memcpy(mem, &cache->res, sizeof(*mem));
 	return 0;
 }
 EXPORT_SYMBOL_GPL(p2sb_bar);
+
+static int __init p2sb_fs_init(void)
+{
+	p2sb_cache_resources();
+	return 0;
+}
+fs_initcall(p2sb_fs_init);
-- 
2.43.0


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2023-12-01 10:47 [PATCH RFC] platform/x86: p2sb: Allow p2sb_bar() calls during PCI device probe Shin'ichiro Kawasaki
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