From: Jason A. Donenfeld <Jason@zx2c4.com>
Date: Sat, 23 Apr 2022 19:11:41 +0000 (+0200)
Subject: openrisc: start CPU timer early in boot
X-Git-Url: http://git.maquefel.me/?a=commitdiff_plain;h=516dd4aacd67a0f27da94f3fe63fe0f4dbab6e2b;p=linux.git

openrisc: start CPU timer early in boot

In order to measure the boot process, the timer should be switched on as
early in boot as possible. As well, the commit defines the get_cycles
macro, like the previous patches in this series, so that generic code is
aware that it's implemented by the platform, as is done on other archs.

Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Jonas Bonn <jonas@southpole.se>
Cc: Stefan Kristiansson <stefan.kristiansson@saunalahti.fi>
Acked-by: Stafford Horne <shorne@gmail.com>
Reported-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
---

diff --git a/arch/openrisc/include/asm/timex.h b/arch/openrisc/include/asm/timex.h
index d52b4e536e3f9..5487fa93dd9be 100644
--- a/arch/openrisc/include/asm/timex.h
+++ b/arch/openrisc/include/asm/timex.h
@@ -23,6 +23,7 @@ static inline cycles_t get_cycles(void)
 {
 	return mfspr(SPR_TTCR);
 }
+#define get_cycles get_cycles
 
 /* This isn't really used any more */
 #define CLOCK_TICK_RATE 1000
diff --git a/arch/openrisc/kernel/head.S b/arch/openrisc/kernel/head.S
index 15f1b38dfe03b..871f4c8588595 100644
--- a/arch/openrisc/kernel/head.S
+++ b/arch/openrisc/kernel/head.S
@@ -521,6 +521,15 @@ _start:
 	l.ori	r3,r0,0x1
 	l.mtspr	r0,r3,SPR_SR
 
+	/*
+	 * Start the TTCR as early as possible, so that the RNG can make use of
+	 * measurements of boot time from the earliest opportunity. Especially
+	 * important is that the TTCR does not return zero by the time we reach
+	 * rand_initialize().
+	 */
+	l.movhi r3,hi(SPR_TTMR_CR)
+	l.mtspr r0,r3,SPR_TTMR
+
 	CLEAR_GPR(r1)
 	CLEAR_GPR(r2)
 	CLEAR_GPR(r3)