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Diffstat (limited to 'arch/mips/kernel/csrc-r4k.c')
-rw-r--r--arch/mips/kernel/csrc-r4k.c44
1 files changed, 44 insertions, 0 deletions
diff --git a/arch/mips/kernel/csrc-r4k.c b/arch/mips/kernel/csrc-r4k.c
index e5ed7ada1..1f910563f 100644
--- a/arch/mips/kernel/csrc-r4k.c
+++ b/arch/mips/kernel/csrc-r4k.c
@@ -28,6 +28,43 @@ static u64 notrace r4k_read_sched_clock(void)
return read_c0_count();
}
+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;
+}
+
int __init init_r4k_clocksource(void)
{
if (!cpu_has_counter || !mips_hpt_frequency)
@@ -36,6 +73,13 @@ int __init init_r4k_clocksource(void)
/* Calculate a somewhat reasonable rating value */
clocksource_mips.rating = 200 + mips_hpt_frequency / 10000000;
+ /*
+ * R2 onwards makes the count accessible to user mode so it can be used
+ * by the VDSO (HWREna is configured by configure_hwrena()).
+ */
+ if (cpu_has_mips_r2_r6 && rdhwr_count_usable())
+ clocksource_mips.archdata.vdso_clock_mode = VDSO_CLOCK_R4K;
+
clocksource_register_hz(&clocksource_mips, mips_hpt_frequency);
sched_clock_register(r4k_read_sched_clock, 32, mips_hpt_frequency);