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author | Grant Likely <grant.likely@secretlab.ca> | 2010-12-23 00:41:14 -0700 |
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committer | Grant Likely <grant.likely@secretlab.ca> | 2010-12-23 00:41:14 -0700 |
commit | cfb13c5db08c90311a5defdde9a0328ee788cca5 (patch) | |
tree | 842cb60d1d19b99e550fdbc653723e4b13e51ee5 /include/linux/cnt32_to_63.h | |
parent | 4b6ba8aacbb3185703b797286547d0f8f3859b02 (diff) | |
parent | 90a8a73c06cc32b609a880d48449d7083327e11a (diff) |
Merge commit 'v2.6.37-rc7' into devicetree/next
Diffstat (limited to 'include/linux/cnt32_to_63.h')
-rw-r--r-- | include/linux/cnt32_to_63.h | 20 |
1 files changed, 19 insertions, 1 deletions
diff --git a/include/linux/cnt32_to_63.h b/include/linux/cnt32_to_63.h index 7605fdd1eb65..e3d8bf26e5eb 100644 --- a/include/linux/cnt32_to_63.h +++ b/include/linux/cnt32_to_63.h @@ -61,13 +61,31 @@ union cnt32_to_63 { * * 2) this code must not be preempted for a duration longer than the * 32-bit counter half period minus the longest period between two - * calls to this code. + * calls to this code; * * Those requirements ensure proper update to the state bit in memory. * This is usually not a problem in practice, but if it is then a kernel * timer should be scheduled to manage for this code to be executed often * enough. * + * And finally: + * + * 3) the cnt_lo argument must be seen as a globally incrementing value, + * meaning that it should be a direct reference to the counter data which + * can be evaluated according to a specific ordering within the macro, + * and not the result of a previous evaluation stored in a variable. + * + * For example, this is wrong: + * + * u32 partial = get_hw_count(); + * u64 full = cnt32_to_63(partial); + * return full; + * + * This is fine: + * + * u64 full = cnt32_to_63(get_hw_count()); + * return full; + * * Note that the top bit (bit 63) in the returned value should be considered * as garbage. It is not cleared here because callers are likely to use a * multiplier on the returned value which can get rid of the top bit |