+static inline unsigned int rdhwr_count(void)
+{
+ unsigned int count;
+
+ __asm__ __volatile__(
+ " .set push\n"
+ " .set mips32r2\n"
+ " rdhwr %0, $2\n"
+ " .set pop\n"
+ : "=r" (count));
+
+ return count;
+}
+
+static bool rdhwr_count_usable(void)
+{
+ unsigned int prev, curr, i;
+
+ /*
+ * Older QEMUs have a broken implementation of RDHWR for the CP0 count
+ * which always returns a constant value. Try to identify this and don't
+ * use it in the VDSO if it is broken. This workaround can be removed
+ * once the fix has been in QEMU stable for a reasonable amount of time.
+ */
+ for (i = 0, prev = rdhwr_count(); i < 100; i++) {
+ curr = rdhwr_count();
+
+ if (curr != prev)
+ return true;
+
+ prev = curr;
+ }
+
+ pr_warn("Not using R4K clocksource in VDSO due to broken RDHWR\n");
+ return false;
+}
+