MIPS: pci-ar724x: avoid data bus error due to a missing PCIe module

If the controller has no PCIe module attached, accessing of the device
configuration space causes a data bus error. Avoid this by checking the
status of the PCIe link in advance, and indicate an error if the link
is down.

Signed-off-by: Gabor Juhos <juhosg@openwrt.org>
Cc: stable@vger.kernel.org
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/4293/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

diff --git a/arch/mips/pci/pci-ar724x.c b/arch/mips/pci/pci-ar724x.c
index 414a7459858d4e06b837a08d375eccbc96804dae..86d77a666458bae80c60f94c9fc405dca5f8459c 100644 (file)
--- a/arch/mips/pci/pci-ar724x.c
+++ b/arch/mips/pci/pci-ar724x.c
@@ -23,9 +23,12 @@
 #define AR724X_PCI_MEM_BASE    0x10000000
 #define AR724X_PCI_MEM_SIZE    0x08000000
 
+#define AR724X_PCI_REG_RESET           0x18
 #define AR724X_PCI_REG_INT_STATUS      0x4c
 #define AR724X_PCI_REG_INT_MASK                0x50
 
+#define AR724X_PCI_RESET_LINK_UP       BIT(0)
+
 #define AR724X_PCI_INT_DEV0            BIT(14)
 
 #define AR724X_PCI_IRQ_COUNT           1
@@ -38,6 +41,15 @@ static void __iomem *ar724x_pci_ctrl_base;
 
 static u32 ar724x_pci_bar0_value;
 static bool ar724x_pci_bar0_is_cached;
+static bool ar724x_pci_link_up;
+
+static inline bool ar724x_pci_check_link(void)
+{
+       u32 reset;
+
+       reset = __raw_readl(ar724x_pci_ctrl_base + AR724X_PCI_REG_RESET);
+       return reset & AR724X_PCI_RESET_LINK_UP;
+}
 
 static int ar724x_pci_read(struct pci_bus *bus, unsigned int devfn, int where,
                            int size, uint32_t *value)
@@ -46,6 +58,9 @@ static int ar724x_pci_read(struct pci_bus *bus, unsigned int devfn, int where,
        void __iomem *base;
        u32 data;
 
+       if (!ar724x_pci_link_up)
+               return PCIBIOS_DEVICE_NOT_FOUND;
+
        if (devfn)
                return PCIBIOS_DEVICE_NOT_FOUND;
 
@@ -96,6 +111,9 @@ static int ar724x_pci_write(struct pci_bus *bus, unsigned int devfn, int where,
        u32 data;
        int s;
 
+       if (!ar724x_pci_link_up)
+               return PCIBIOS_DEVICE_NOT_FOUND;
+
        if (devfn)
                return PCIBIOS_DEVICE_NOT_FOUND;
 
@@ -280,6 +298,10 @@ int __init ar724x_pcibios_init(int irq)
        if (ar724x_pci_ctrl_base == NULL)
                goto err_unmap_devcfg;
 
+       ar724x_pci_link_up = ar724x_pci_check_link();
+       if (!ar724x_pci_link_up)
+               pr_warn("ar724x: PCIe link is down\n");
+
        ar724x_pci_irq_init(irq);
        register_pci_controller(&ar724x_pci_controller);