[PATCH RFC v1 03/10] riscv: use sched_clock() for random_get_entropy() instead of zero

[Jason A. Donenfeld]

In the event that random_get_entropy() can't access a cycle counter or
similar, falling back to returning 0 is really not the best we can do.
Instead, at least calling sched_clock() would be preferable, because
that always needs to return _something_, even falling back to jiffies
eventually. It's not as though sched_clock() is super high precision or
guaranteed to be entropic, but basically anything that's not zero all
the time is better than returning zero all the time.

Cc: Arnd Bergmann <arnd@xxxxxxxx>
Cc: Paul Walmsley <paul.walmsley@xxxxxxxxxx>
Cc: Palmer Dabbelt <palmer@xxxxxxxxxxx>
Signed-off-by: Jason A. Donenfeld <Jason@xxxxxxxxx>
---
 arch/riscv/include/asm/timex.h | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/arch/riscv/include/asm/timex.h b/arch/riscv/include/asm/timex.h
index 507cae273bc6..5b802755ca3a 100644
--- a/arch/riscv/include/asm/timex.h
+++ b/arch/riscv/include/asm/timex.h
@@ -7,6 +7,7 @@
 #define _ASM_RISCV_TIMEX_H
 
 #include <asm/csr.h>
+#include <linux/sched/clock.h>
 
 typedef unsigned long cycles_t;
 
@@ -41,7 +42,7 @@ static inline u32 get_cycles_hi(void)
 static inline unsigned long random_get_entropy(void)
 {
 	if (unlikely(clint_time_val == NULL))
-		return 0;
+		return sched_clock();
 	return get_cycles();
 }
 #define random_get_entropy()	random_get_entropy()
-- 
2.35.1