The LC bit in the PMCR_EL0 register is supposed to be:
 * read/write
 * RES1 on an AArch64-only implementation
 * an architecturally UNKNOWN value on reset
(and use of LC==0 by software is deprecated).

We were implementing it incorrectly as read-only always zero,
though we do have all the code needed to test it and behave
accordingly.

Instead make it a read-write bit which resets to 1 always, which
satisfies all the architectural requirements above.

Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
---
 target/arm/helper.c | 13 +++++++++----
 1 file changed, 9 insertions(+), 4 deletions(-)

diff --git a/target/arm/helper.c b/target/arm/helper.c
index 2ebfa6c6545..468e4e89848 100644
--- a/target/arm/helper.c
+++ b/target/arm/helper.c
@@ -1023,6 +1023,11 @@ static const ARMCPRegInfo v6_cp_reginfo[] = {
 #define PMCRC   0x4
 #define PMCRP   0x2
 #define PMCRE   0x1
+/*
+ * Mask of PMCR bits writeable by guest (not including WO bits like C, P,
+ * which can be written as 1 to trigger behaviour but which stay RAZ).
+ */
+#define PMCR_WRITEABLE_MASK (PMCRLC | PMCRDP | PMCRX | PMCRD | PMCRE)
 
 #define PMXEVTYPER_P          0x80000000
 #define PMXEVTYPER_U          0x40000000
@@ -1577,9 +1582,8 @@ static void pmcr_write(CPUARMState *env, const ARMCPRegInfo *ri,
         }
     }
 
-    /* only the DP, X, D and E bits are writable */
-    env->cp15.c9_pmcr &= ~0x39;
-    env->cp15.c9_pmcr |= (value & 0x39);
+    env->cp15.c9_pmcr &= ~PMCR_WRITEABLE_MASK;
+    env->cp15.c9_pmcr |= (value & PMCR_WRITEABLE_MASK);
 
     pmu_op_finish(env);
 }
@@ -6370,7 +6374,8 @@ static void define_pmu_regs(ARMCPU *cpu)
         .access = PL0_RW, .accessfn = pmreg_access,
         .type = ARM_CP_IO,
         .fieldoffset = offsetof(CPUARMState, cp15.c9_pmcr),
-        .resetvalue = (cpu->midr & 0xff000000) | (pmcrn << PMCRN_SHIFT),
+        .resetvalue = (cpu->midr & 0xff000000) | (pmcrn << PMCRN_SHIFT) |
+                      PMCRLC,
         .writefn = pmcr_write, .raw_writefn = raw_write,
     };
     define_one_arm_cp_reg(cpu, &pmcr);
-- 
2.20.1