arm: Implement PMCCNTR 32b read-modify-write

The register is now 64bit, however a 32 bit write to the register
should leave the higher bits unchanged. The open coded write handler
does not implement this, so we need to read-modify-write accordingly.
Signed-off-by: NPeter Crosthwaite <peter.crosthwaite@xilinx.com>
Reviewed-by: NAlistair Francis <alistair23@gmail.com>
Message-id: ec350573424bb2adc1701c3b9278d26598e2f2d1.1409025949.git.peter.crosthwaite@xilinx.com
Signed-off-by: NPeter Maydell <peter.maydell@linaro.org>

target-arm/helper.c

@@ -623,6 +623,15 @@ static void pmccntr_write(CPUARMState *env, const ARMCPRegInfo *ri,
     }
     env->cp15.c15_ccnt = total_ticks - value;
 }
+
+static void pmccntr_write32(CPUARMState *env, const ARMCPRegInfo *ri,
+                            uint64_t value)
+{
+    uint64_t cur_val = pmccntr_read(env, NULL);
+
+    pmccntr_write(env, ri, deposit64(cur_val, 0, 32, value));
+}
+
 #endif
 
 static void pmcntenset_write(CPUARMState *env, const ARMCPRegInfo *ri,
@@ -754,7 +763,7 @@ static const ARMCPRegInfo v7_cp_reginfo[] = {
 #ifndef CONFIG_USER_ONLY
     { .name = "PMCCNTR", .cp = 15, .crn = 9, .crm = 13, .opc1 = 0, .opc2 = 0,
       .access = PL0_RW, .resetvalue = 0, .type = ARM_CP_IO,
-      .readfn = pmccntr_read, .writefn = pmccntr_write,
+      .readfn = pmccntr_read, .writefn = pmccntr_write32,
       .accessfn = pmreg_access },
 #endif
     { .name = "PMXEVTYPER", .cp = 15, .crn = 9, .crm = 13, .opc1 = 0, .opc2 = 1,