[PATCH v10 4/6] ARM: add vdso user-space code

On Fri, Feb 13, 2015 at 04:36:25AM +0000, Venkappa Mala wrote:

Nathan Lynch <nathan_lynch <at> mentor.com> writes:

quoted

+#ifdef CONFIG_ARM_ARCH_TIMER
+
+static notrace u64 get_ns(struct vdso_data *vdata)
+{
+	u64 cycle_delta;
+	u64 cycle_now;
+	u64 nsec;
+
+	cycle_now = arch_counter_get_cntvct();

Regarding ARM:vDSO, I have enabled your patch set on Cortex-A7/ARMv7, 
the vDSO is up and running using generic arch timer using physical 
counter but not with VCT.
I anticipate, the issue could be due to VCT cycles.

[...]

Perhaps, either we need to revise the vDSO frame work to choose VCT or 
PCT dynamically Otherwise CNTVOFF reset to be zero but CNTVOFF could not 
be accessed in SVC mode (PL1).

I assume on your platform, the DT also contains
"arm,cpu-registers-not-fw-configured". In such case, the VDSO
optimisation for gettimeofday should just be disabled (as it would be if
the generic timers are not present). Really, just fix the firmware.

-- 
Catalin