[PATCH v3] Loongson: Lemote-2F: Fixup of _rdmsr and _wrmsr

[Wu Zhangjin <wuzhangjin@gmail.com>]

From: Wu Zhangjin <wuzhangjin@gmail.com>

v2 --> v3:
  o Using the right operations for the raw spinlock.
v1 --> v2:
  o Using raw spinlock instead of spinlock as suggested by David Daney.

The _rdmsr, _wrmsr operation must be atomic to ensure the accessing to msr
address is what we want.

Without this patch, in some cases, the reboot operation(fs2f_reboot) defined in
arch/mips/loongson/lemote-2f/reset.c may fail for it called _rdmsr, _wrmsr but
may be interrupted/preempted by the other related operations and make the
_rdmsr get the wrong value or make the _wrmsr write a wrong value to an
unexpected target.

Signed-off-by: Wu Zhangjin <wuzhangjin@gmail.com>
---
 arch/mips/pci/ops-loongson2.c |   10 ++++++++++
 1 files changed, 10 insertions(+), 0 deletions(-)

diff --git a/arch/mips/pci/ops-loongson2.c b/arch/mips/pci/ops-loongson2.c
index 2bb4057..d657ee0 100644
--- a/arch/mips/pci/ops-loongson2.c
+++ b/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
-- 
1.7.0.1