linux-kernel - [PATCH v7 11/17] openrisc: account for 0 starting value in random_get

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Date:   Fri, 29 Apr 2022 02:16:48 +0200
From:   "Jason A. Donenfeld" <Jason@...c4.com>
To:     linux-kernel@...r.kernel.org, linux-crypto@...r.kernel.org
Cc:     Stafford Horne <shorne@...il.com>,
        "Jason A. Donenfeld" <Jason@...c4.com>
Subject: [PATCH v7 11/17] openrisc: account for 0 starting value in random_get_entropy()

As a sanity check, this series makes sure that during early boot, the
cycle counter isn't returning all zeros. However, OpenRISC's TTCR timer
can be rather slow and starts out as zero during stages of early boot.
We know it works, however. So just always add 1 to random_get_entropy()
so that it doesn't trigger these checks.

Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: Arnd Bergmann <arnd@...db.de>
Cc: Jonas Bonn <jonas@...thpole.se>
Cc: Stefan Kristiansson <stefan.kristiansson@...nalahti.fi>
Acked-by: Stafford Horne <shorne@...il.com>
Signed-off-by: Jason A. Donenfeld <Jason@...c4.com>
---
Changes v6->v7:
- Add 1 to cycle counter to account for functional but slow-to-begin
  counter on QEMU.

 arch/openrisc/include/asm/timex.h | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/arch/openrisc/include/asm/timex.h b/arch/openrisc/include/asm/timex.h
index d52b4e536e3f..a78a5807c927 100644
--- a/arch/openrisc/include/asm/timex.h
+++ b/arch/openrisc/include/asm/timex.h
@@ -23,6 +23,9 @@ static inline cycles_t get_cycles(void)
 {
 	return mfspr(SPR_TTCR);
 }
+#define get_cycles get_cycles
+
+#define random_get_entropy() ((unsigned long)get_cycles() + 1)
 
 /* This isn't really used any more */
 #define CLOCK_TICK_RATE 1000
-- 
2.35.1