MIPS: CM: Avoid per-core locking with CM3 & higher

CM3 provides a GCR_CL_OTHER register per VP, rather than only per core.
This means that we don't need to prevent other VPs within a core from
racing with code that makes use of the core-other register region.

Reduce locking overhead by demoting the per-core spinlock providing
protection for CM2.5 & lower to a per-CPU/per-VP spinlock for CM3 &
higher.

Signed-off-by: Paul Burton <paul.burton@imgtec.com>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/16193/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

diff --git a/arch/mips/kernel/mips-cm.c b/arch/mips/kernel/mips-cm.c
index 659e6d3..99bb74d 100644 (file)
--- a/arch/mips/kernel/mips-cm.c
+++ b/arch/mips/kernel/mips-cm.c
@@ -265,15 +265,34 @@ void mips_cm_lock_other(unsigned int core, unsigned int vp)
        u32 val;
 
        preempt_disable();
-       curr_core = current_cpu_data.core;
-       spin_lock_irqsave(&per_cpu(cm_core_lock, curr_core),
-                         per_cpu(cm_core_lock_flags, curr_core));
 
        if (mips_cm_revision() >= CM_REV_CM3) {
                val = core << CM3_GCR_Cx_OTHER_CORE_SHF;
                val |= vp << CM3_GCR_Cx_OTHER_VP_SHF;
+
+               /*
+                * We need to disable interrupts in SMP systems in order to
+                * ensure that we don't interrupt the caller with code which
+                * may modify the redirect register. We do so here in a
+                * slightly obscure way by using a spin lock, since this has
+                * the neat property of also catching any nested uses of
+                * mips_cm_lock_other() leading to a deadlock or a nice warning
+                * with lockdep enabled.
+                */
+               spin_lock_irqsave(this_cpu_ptr(&cm_core_lock),
+                                 *this_cpu_ptr(&cm_core_lock_flags));
        } else {
                BUG_ON(vp != 0);
+
+               /*
+                * We only have a GCR_CL_OTHER per core in systems with
+                * CM 2.5 & older, so have to ensure other VP(E)s don't
+                * race with us.
+                */
+               curr_core = current_cpu_data.core;
+               spin_lock_irqsave(&per_cpu(cm_core_lock, curr_core),
+                                 per_cpu(cm_core_lock_flags, curr_core));
+
                val = core << CM_GCR_Cx_OTHER_CORENUM_SHF;
        }
 
@@ -288,10 +307,17 @@ void mips_cm_lock_other(unsigned int core, unsigned int vp)
 
 void mips_cm_unlock_other(void)
 {
-       unsigned curr_core = current_cpu_data.core;
+       unsigned int curr_core;
+
+       if (mips_cm_revision() < CM_REV_CM3) {
+               curr_core = current_cpu_data.core;
+               spin_unlock_irqrestore(&per_cpu(cm_core_lock, curr_core),
+                                      per_cpu(cm_core_lock_flags, curr_core));
+       } else {
+               spin_unlock_irqrestore(this_cpu_ptr(&cm_core_lock),
+                                      *this_cpu_ptr(&cm_core_lock_flags));
+       }
 
-       spin_unlock_irqrestore(&per_cpu(cm_core_lock, curr_core),
-                              per_cpu(cm_core_lock_flags, curr_core));
        preempt_enable();
 }