[MIPS] SMTC: Interrupt mask backstop hack

To support multiple TC microthreads acting as "CPUs" within a VPE,
VPE-wide interrupt mask bits must be specially manipulated during
interrupt handling. To support legacy drivers and interrupt controller
management code, SMTC has a "backstop" to track and if necessary restore
the interrupt mask. This has some performance impact on interrupt service
overhead. Disable it only if you know what you are doing.

Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

diff --git a/arch/mips/Kconfig b/arch/mips/Kconfig
index a00fabe..49f02e3 100644 (file)
--- a/arch/mips/Kconfig
+++ b/arch/mips/Kconfig
@@ -1404,6 +1404,19 @@ config MIPS_MT_SMTC_INSTANT_REPLAY
          it off), but ensures that IPIs are handled promptly even under
          heavy I/O interrupt load.
 
+config MIPS_MT_SMTC_IM_BACKSTOP
+       bool "Use per-TC register bits as backstop for inhibited IM bits"
+       depends on MIPS_MT_SMTC
+       default y
+       help
+         To support multiple TC microthreads acting as "CPUs" within
+         a VPE, VPE-wide interrupt mask bits must be specially manipulated
+         during interrupt handling. To support legacy drivers and interrupt
+         controller management code, SMTC has a "backstop" to track and
+         if necessary restore the interrupt mask. This has some performance
+         impact on interrupt service overhead. Disable it only if you know
+         what you are doing.
+
 config MIPS_VPE_LOADER_TOM
        bool "Load VPE program into memory hidden from linux"
        depends on MIPS_VPE_LOADER

diff --git a/arch/mips/kernel/entry.S b/arch/mips/kernel/entry.S
index 686249c..e29598a 100644 (file)
--- a/arch/mips/kernel/entry.S
+++ b/arch/mips/kernel/entry.S
@@ -84,6 +84,7 @@ FEXPORT(restore_all)                  # restore full frame
        LONG_S  sp, TI_REGS($28)
        jal     deferred_smtc_ipi
        LONG_S  s0, TI_REGS($28)
+#ifdef CONFIG_MIPS_MT_SMTC_IM_BACKSTOP
 /* Re-arm any temporarily masked interrupts not explicitly "acked" */
        mfc0    v0, CP0_TCSTATUS
        ori     v1, v0, TCSTATUS_IXMT
@@ -110,6 +111,7 @@ FEXPORT(restore_all)                        # restore full frame
        _ehb
        xor     t0, t0, t3
        mtc0    t0, CP0_TCCONTEXT
+#endif /* CONFIG_MIPS_MT_SMTC_IM_BACKSTOP */
 #endif /* CONFIG_MIPS_MT_SMTC */
        .set    noat
        RESTORE_TEMP

diff --git a/arch/mips/kernel/genex.S b/arch/mips/kernel/genex.S
index 297bd56..c0f19d6 100644 (file)
--- a/arch/mips/kernel/genex.S
+++ b/arch/mips/kernel/genex.S
@@ -243,9 +243,11 @@ NESTED(except_vec_vi_handler, 0, sp)
         */
        mfc0    t1, CP0_STATUS
        and     t0, a0, t1
+#ifdef CONFIG_MIPS_MT_SMTC_IM_BACKSTOP
        mfc0    t2, CP0_TCCONTEXT
        or      t0, t0, t2
        mtc0    t0, CP0_TCCONTEXT
+#endif /* CONFIG_MIPS_MT_SMTC_IM_BACKSTOP */
        xor     t1, t1, t0
        mtc0    t1, CP0_STATUS
        _ehb

diff --git a/include/asm-mips/irq.h b/include/asm-mips/irq.h
index 3ca6a07..97102eb 100644 (file)
--- a/include/asm-mips/irq.h
+++ b/include/asm-mips/irq.h
@@ -24,7 +24,7 @@ static inline int irq_canonicalize(int irq)
 #define irq_canonicalize(irq) (irq)    /* Sane hardware, sane code ... */
 #endif
 
-#ifdef CONFIG_MIPS_MT_SMTC
+#ifdef CONFIG_MIPS_MT_SMTC_IM_BACKSTOP
 /*
  * Clear interrupt mask handling "backstop" if irq_hwmask
  * entry so indicates. This implies that the ack() or end()