[PATCH v2 2/4] hw/arm/sbsa-ref: Force CPU generic timer to 62.5MHz

[Peter Maydell]

Currently QEMU CPUs always run with a generic timer counter frequency
of 62.5MHz, but ARMv8.6 CPUs will run at 1GHz.  For older versions of
the TF-A firmware that sbsa-ref runs, the frequency of the generic
timer is hardcoded into the firmware, and so if the CPU actually has
a different frequency then timers in the guest will be set
incorrectly.

The default frequency used by the 'max' CPU is about to change, so
make the sbsa-ref board force the CPU frequency to the value which
the firmware expects.

Newer versions of TF-A will read the frequency from the CPU's
CNTFRQ_EL0 register:
 
https://github.com/ARM-software/arm-trusted-firmware/commit/4c77fac98dac0bebc63798aae9101ac865b87148
so in the longer term we could make this board use the 1GHz
frequency. We will need to make sure we update the binaries used
by our avocado test
 Aarch64SbsarefMachine.test_sbsaref_alpine_linux_max_pauth_impdef
before we can do that.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
---
I leave it up to the sbsa-ref maintainers exactly when they
want to shift to 1GHz (probably after a TF-A release with the fix?)
---
 hw/arm/sbsa-ref.c | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/hw/arm/sbsa-ref.c b/hw/arm/sbsa-ref.c
index f5709d6c141..36f6f717b4b 100644
--- a/hw/arm/sbsa-ref.c
+++ b/hw/arm/sbsa-ref.c
@@ -60,6 +60,19 @@
 #define NUM_SMMU_IRQS   4
 #define NUM_SATA_PORTS  6
 
+/*
+ * Generic timer frequency in Hz (which drives both the CPU generic timers
+ * and the SBSA watchdog-timer). Older versions of the TF-A firmware
+ * typically used with sbsa-ref (including the binaries in our Avocado test
+ * Aarch64SbsarefMachine.test_sbsaref_alpine_linux_max_pauth_impdef
+ * assume it is this value.
+ *
+ * TODO: this value is not architecturally correct for an Armv8.6 or
+ * better CPU, so we should move to 1GHz once the TF-A fix above has
+ * made it into a release and into our Avocado test.
+ */
+#define SBSA_GTIMER_HZ 62500000
+
 enum {
     SBSA_FLASH,
     SBSA_MEM,
@@ -767,6 +780,8 @@ static void sbsa_ref_init(MachineState *machine)
                                     &error_abort);
         }
 
+        object_property_set_int(cpuobj, "cntfrq", SBSA_GTIMER_HZ, 
&error_abort);
+
         object_property_set_link(cpuobj, "memory", OBJECT(sysmem),
                                  &error_abort);
 
-- 
2.34.1