MIPS: Lemote 2F: Ensure atomic execution of _rdmsr and _wrmsr

On Lemote 2F CS5536 MSRs are accessed through a index / data register pair.
The access sequence must be protected by a spinlock to be atomic.

Without this rebooting in fs2f_reboot() may fail.

Signed-off-by: Wu Zhangjin <wuzhangjin@gmail.com>
Cc: linux-mips@linux-mips.org
Cc: David Daney <ddaney@caviumnetworks.com>
Patchwork: http://patchwork.linux-mips.org/patch/1058/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

arch/mips/pci/ops-loongson2.c

@@ -180,15 +180,21 @@ struct pci_ops loongson_pci_ops = {
 };
 
 #ifdef CONFIG_CS5536
+DEFINE_RAW_SPINLOCK(msr_lock);
+
 void _rdmsr(u32 msr, u32 *hi, u32 *lo)
 {
 	struct pci_bus bus = {
 		.number = PCI_BUS_CS5536
 	};
 	u32 devfn = PCI_DEVFN(PCI_IDSEL_CS5536, 0);
+	unsigned long flags;
+
+	raw_spin_lock_irqsave(&msr_lock, flags);
 	loongson_pcibios_write(&bus, devfn, PCI_MSR_ADDR, 4, msr);
 	loongson_pcibios_read(&bus, devfn, PCI_MSR_DATA_LO, 4, lo);
 	loongson_pcibios_read(&bus, devfn, PCI_MSR_DATA_HI, 4, hi);
+	raw_spin_unlock_irqrestore(&msr_lock, flags);
 }
 EXPORT_SYMBOL(_rdmsr);
 
@@ -198,9 +204,13 @@ void _wrmsr(u32 msr, u32 hi, u32 lo)
 		.number = PCI_BUS_CS5536
 	};
 	u32 devfn = PCI_DEVFN(PCI_IDSEL_CS5536, 0);
+	unsigned long flags;
+
+	raw_spin_lock_irqsave(&msr_lock, flags);
 	loongson_pcibios_write(&bus, devfn, PCI_MSR_ADDR, 4, msr);
 	loongson_pcibios_write(&bus, devfn, PCI_MSR_DATA_LO, 4, lo);
 	loongson_pcibios_write(&bus, devfn, PCI_MSR_DATA_HI, 4, hi);
+	raw_spin_unlock_irqrestore(&msr_lock, flags);
 }
 EXPORT_SYMBOL(_wrmsr);
 #endif