[PATCH V15 4/7] PCI: loongson: Don't access non-existant devices

[Huacai Chen <chenhuacai@xxxxxxxxxxx>]

On LS2K/LS7A, some non-existant devices don't return 0xffffffff when
scanning (they are hidden devices for debug in fact, access the config
space may cause machine hang). This is a hardware flaw but we can only
avoid it by software now.

Signed-off-by: Huacai Chen <chenhuacai@xxxxxxxxxxx>
---
 drivers/pci/controller/pci-loongson.c | 30 +++++++++++++++++++++------
 1 file changed, 24 insertions(+), 6 deletions(-)

diff --git a/drivers/pci/controller/pci-loongson.c b/drivers/pci/controller/pci-loongson.c
index a1222fc15454..de5be6d9bcbc 100644
--- a/drivers/pci/controller/pci-loongson.c
+++ b/drivers/pci/controller/pci-loongson.c
@@ -26,6 +26,7 @@
 #define FLAG_CFG0	BIT(0)
 #define FLAG_CFG1	BIT(1)
 #define FLAG_DEV_FIX	BIT(2)
+#define FLAG_DEV_HIDDEN	BIT(3)
 
 struct loongson_pci_data {
 	u32 flags;
@@ -134,10 +135,17 @@ static void __iomem *cfg0_map(struct loongson_pci *priv, int bus,
 	return priv->cfg0_base + addroff;
 }
 
+static bool pdev_may_exist(struct pci_bus *bus, unsigned int device, unsigned int function)
+{
+	return !(pci_is_root_bus(bus) && (device >= 9 && device <= 20) && (function > 0));
+}
+
 static void __iomem *pci_loongson_map_bus(struct pci_bus *bus, unsigned int devfn,
 			       int where)
 {
 	unsigned char busnum = bus->number;
+	unsigned int device = PCI_SLOT(devfn);
+	unsigned int function = PCI_FUNC(devfn);
 	struct loongson_pci *priv = pci_bus_to_loongson_pci(bus);
 
 	if (pci_is_root_bus(bus))
@@ -147,9 +158,16 @@ static void __iomem *pci_loongson_map_bus(struct pci_bus *bus, unsigned int devf
 	 * Do not read more than one device on the bus other than
 	 * the host bus.
 	 */
-	if (priv->data->flags & FLAG_DEV_FIX &&
-			!pci_is_root_bus(bus) && PCI_SLOT(devfn) > 0)
-		return NULL;
+	if ((priv->data->flags & FLAG_DEV_FIX) && bus->self) {
+		if (!pci_is_root_bus(bus) && (device > 0))
+			return NULL;
+	}
+
+	/* Don't access non-existant devices */
+	if (priv->data->flags & FLAG_DEV_HIDDEN) {
+		if (!pdev_may_exist(bus, device, function))
+			return NULL;
+	}
 
 	/* CFG0 can only access standard space */
 	if (where < PCI_CFG_SPACE_SIZE && priv->cfg0_base)
@@ -197,12 +215,12 @@ static struct pci_ops loongson_pci_ops32 = {
 };
 
 static const struct loongson_pci_data ls2k_pci_data = {
-	.flags = FLAG_CFG1 | FLAG_DEV_FIX,
+	.flags = FLAG_CFG1 | FLAG_DEV_FIX | FLAG_DEV_HIDDEN,
 	.ops = &loongson_pci_ops,
 };
 
 static const struct loongson_pci_data ls7a_pci_data = {
-	.flags = FLAG_CFG1 | FLAG_DEV_FIX,
+	.flags = FLAG_CFG1 | FLAG_DEV_FIX | FLAG_DEV_HIDDEN,
 	.ops = &loongson_pci_ops,
 };
 
@@ -297,7 +315,7 @@ static int loongson_pci_ecam_init(struct pci_config_window *cfg)
 		return -ENOMEM;
 
 	cfg->priv = priv;
-	data->flags = FLAG_CFG1;
+	data->flags = FLAG_CFG1 | FLAG_DEV_HIDDEN;
 	priv->data = data;
 	priv->cfg1_base = cfg->win - (cfg->busr.start << 16);
 
-- 
2.27.0