mirror of
https://github.com/openwrt/openwrt.git
synced 2024-12-28 17:48:58 +00:00
eea5c0b166
get_cycles() is used in some places as one part of the seed for the kernel PRNG. This backports the following commit from mainline linux kernel: 9c9b415c50bc298ac61412dff856eae2f54889ee Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de> SVN-Revision: 38834
70 lines
1.9 KiB
Diff
70 lines
1.9 KiB
Diff
From 9c9b415c50bc298ac61412dff856eae2f54889ee Mon Sep 17 00:00:00 2001
|
|
From: Ralf Baechle <ralf@linux-mips.org>
|
|
Date: Thu, 12 Sep 2013 13:47:32 +0200
|
|
Subject: [PATCH] MIPS: Reimplement get_cycles().
|
|
|
|
This essentially reverts commit efb9ca08b5a2374b29938cdcab417ce4feb14b54
|
|
(kernel.org) / 58020a106879a8b372068741c81f0015c9b0b96dbv [[MIPS] Change
|
|
get_cycles to always return 0.]
|
|
|
|
Most users of get_cycles() invoke it as a timing interface. That's why
|
|
in modern kernels it was never very much missed for. /dev/random however
|
|
uses get_cycles() in the how the jitter in the interrupt timing contains
|
|
some useful entropy.
|
|
|
|
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
|
|
---
|
|
arch/mips/include/asm/timex.h | 33 ++++++++++++++++++++++++++++++++-
|
|
1 file changed, 32 insertions(+), 1 deletion(-)
|
|
|
|
--- a/arch/mips/include/asm/timex.h
|
|
+++ b/arch/mips/include/asm/timex.h
|
|
@@ -10,6 +10,7 @@
|
|
|
|
#ifdef __KERNEL__
|
|
|
|
+#include <asm/cpu-features.h>
|
|
#include <asm/mipsregs.h>
|
|
|
|
/*
|
|
@@ -33,9 +34,38 @@
|
|
|
|
typedef unsigned int cycles_t;
|
|
|
|
+/*
|
|
+ * On R4000/R4400 before version 5.0 an erratum exists such that if the
|
|
+ * cycle counter is read in the exact moment that it is matching the
|
|
+ * compare register, no interrupt will be generated.
|
|
+ *
|
|
+ * There is a suggested workaround and also the erratum can't strike if
|
|
+ * the compare interrupt isn't being used as the clock source device.
|
|
+ * However for now the implementaton of this function doesn't get these
|
|
+ * fine details right.
|
|
+ */
|
|
static inline cycles_t get_cycles(void)
|
|
{
|
|
- return 0;
|
|
+ switch (cpu_data[0].cputype) {
|
|
+ case CPU_R4400PC:
|
|
+ case CPU_R4400SC:
|
|
+ case CPU_R4400MC:
|
|
+ if ((read_c0_prid() & 0xff) >= 0x0050)
|
|
+ return read_c0_count();
|
|
+ break;
|
|
+
|
|
+ case CPU_R4000PC:
|
|
+ case CPU_R4000SC:
|
|
+ case CPU_R4000MC:
|
|
+ break;
|
|
+
|
|
+ default:
|
|
+ if (cpu_has_counter)
|
|
+ return read_c0_count();
|
|
+ break;
|
|
+ }
|
|
+
|
|
+ return 0; /* no usable counter */
|
|
}
|
|
|
|
#endif /* __KERNEL__ */
|