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author | Theodore Ts'o <tytso@mit.edu> | 2013-09-21 21:58:22 +0400 |
---|---|---|
committer | Ben Hutchings <ben@decadent.org.uk> | 2013-11-28 18:02:03 +0400 |
commit | ee698d67a4af1fd37ba5b40733f103a62f223774 (patch) | |
tree | 37238290039918cfdc4765548ae8dd5e026cbcf4 /include | |
parent | 52d4f668a2ebb3d33b2ece452d4f3bcec6c87b7d (diff) | |
download | linux-ee698d67a4af1fd37ba5b40733f103a62f223774.tar.xz |
random: allow architectures to optionally define random_get_entropy()
commit 61875f30daf60305712e25b209ef41ced2635bad upstream.
Allow architectures which have a disabled get_cycles() function to
provide a random_get_entropy() function which provides a fine-grained,
rapidly changing counter that can be used by the /dev/random driver.
For example, an architecture might have a rapidly changing register
used to control random TLB cache eviction, or DRAM refresh that
doesn't meet the requirements of get_cycles(), but which is good
enough for the needs of the random driver.
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
Diffstat (limited to 'include')
-rw-r--r-- | include/linux/timex.h | 14 |
1 files changed, 14 insertions, 0 deletions
diff --git a/include/linux/timex.h b/include/linux/timex.h index 08e90fb81acc..5fee575ebccf 100644 --- a/include/linux/timex.h +++ b/include/linux/timex.h @@ -173,6 +173,20 @@ struct timex { #include <asm/timex.h> +#ifndef random_get_entropy +/* + * The random_get_entropy() function is used by the /dev/random driver + * in order to extract entropy via the relative unpredictability of + * when an interrupt takes places versus a high speed, fine-grained + * timing source or cycle counter. Since it will be occurred on every + * single interrupt, it must have a very low cost/overhead. + * + * By default we use get_cycles() for this purpose, but individual + * architectures may override this in their asm/timex.h header file. + */ +#define random_get_entropy() get_cycles() +#endif + /* * SHIFT_PLL is used as a dampening factor to define how much we * adjust the frequency correction for a given offset in PLL mode. |