[ARM] Kirkwood: enable PCIe before reading device ID register

PCIe may have been disabled (by kirkwood_clock_gate)
if this kernel was started by kexec.  Make sure PCIe
is enabled before attempting to access the device ID
register, otherwise the system will hang.
Signed-off-by: Eric Cooper <ecc@cmu.edu>
Signed-off-by: Nicolas Pitre <nico@fluxnic.net>

arch/arm/mach-kirkwood/common.h

@@ -32,6 +32,7 @@ void kirkwood_init_irq(void);
 extern struct mbus_dram_target_info kirkwood_mbus_dram_info;
 void kirkwood_setup_cpu_mbus(void);
 
+void kirkwood_enable_pcie(void);
 void kirkwood_pcie_id(u32 *dev, u32 *rev);
 
 void kirkwood_ehci_init(void);

arch/arm/mach-kirkwood/pcie.c

@@ -18,8 +18,16 @@
 #include <mach/bridge-regs.h>
 #include "common.h"
 
+void kirkwood_enable_pcie(void)
+{
+	u32 curr = readl(CLOCK_GATING_CTRL);
+	if (!(curr & CGC_PEX0))
+		writel(curr | CGC_PEX0, CLOCK_GATING_CTRL);
+}
+
 void __init kirkwood_pcie_id(u32 *dev, u32 *rev)
 {
+	kirkwood_enable_pcie();
 	*dev = orion_pcie_dev_id((void __iomem *)PCIE_VIRT_BASE);
 	*rev = orion_pcie_rev((void __iomem *)PCIE_VIRT_BASE);
 }