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ath5k/ath9k: Fix 64 bits TSF reads

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According to tests, both TSF lower and upper registers kept counting, so
the higher part could have been updated after the lower part has been
read, as shown in the following log where the upper part is read first
and the lower part next.

tsf = {00000003-fffffffd}
tsf = {00000003-00000001}
tsf = {00000004-0000000b}

This patch corrects this by checking that the upper part has not been
changed while the lower part was read. It has been tested in an IBSS
network where artifical IBSS merges have been done in order to trigger
hundreds of rollover for the TSF lower part.

It follows the logic mentionned by Derek, with only 2 register reads
needed at each additional steps instead of 3 (the minimum number of
register reads is still 3).

Signed-off-by: Benoit Papillault <benoit.papillault@free.fr>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
This commit is contained in:
Benoit Papillault 2010-04-16 00:07:26 +02:00 committed by John W. Linville
parent 733f0ea449
commit 1c0fc65e6d
2 changed files with 44 additions and 6 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

31
drivers/net/wireless/ath/ath5k/pcu.c
View File

@ -496,6 +496,8 @@ void ath5k_hw_set_rx_filter(struct ath5k_hw *ah, u32 filter)
* Beacon control *
\****************/
#define ATH5K_MAX_TSF_READ 10
/**
* ath5k_hw_get_tsf64 - Get the full 64bit TSF
*
@ -505,10 +507,35 @@ void ath5k_hw_set_rx_filter(struct ath5k_hw *ah, u32 filter)
*/
u64 ath5k_hw_get_tsf64(struct ath5k_hw *ah)
{
u64 tsf = ath5k_hw_reg_read(ah, AR5K_TSF_U32);
u32 tsf_lower, tsf_upper1, tsf_upper2;
int i;
/*
* While reading TSF upper and then lower part, the clock is still
* counting (or jumping in case of IBSS merge) so we might get
* inconsistent values. To avoid this, we read the upper part again
* and check it has not been changed. We make the hypothesis that a
* maximum of 3 changes can happens in a row (we use 10 as a safe
* value).
*
* Impact on performance is pretty small, since in most cases, only
* 3 register reads are needed.
*/
tsf_upper1 = ath5k_hw_reg_read(ah, AR5K_TSF_U32);
for (i = 0; i < ATH5K_MAX_TSF_READ; i++) {
tsf_lower = ath5k_hw_reg_read(ah, AR5K_TSF_L32);
tsf_upper2 = ath5k_hw_reg_read(ah, AR5K_TSF_U32);
if (tsf_upper2 == tsf_upper1)
break;
tsf_upper1 = tsf_upper2;
}
WARN_ON( i == ATH5K_MAX_TSF_READ );
ATH5K_TRACE(ah->ah_sc);
return ath5k_hw_reg_read(ah, AR5K_TSF_L32) | (tsf << 32);
return (((u64)tsf_upper1 << 32) | tsf_lower);
}
/**

19
drivers/net/wireless/ath/ath9k/hw.c
View File

@ -2420,14 +2420,25 @@ void ath9k_hw_write_associd(struct ath_hw *ah)
}
EXPORT_SYMBOL(ath9k_hw_write_associd);
#define ATH9K_MAX_TSF_READ 10
u64 ath9k_hw_gettsf64(struct ath_hw *ah)
{
u64 tsf;
u32 tsf_lower, tsf_upper1, tsf_upper2;
int i;
tsf = REG_READ(ah, AR_TSF_U32);
tsf = (tsf << 32) | REG_READ(ah, AR_TSF_L32);
tsf_upper1 = REG_READ(ah, AR_TSF_U32);
for (i = 0; i < ATH9K_MAX_TSF_READ; i++) {
tsf_lower = REG_READ(ah, AR_TSF_L32);
tsf_upper2 = REG_READ(ah, AR_TSF_U32);
if (tsf_upper2 == tsf_upper1)
break;
tsf_upper1 = tsf_upper2;
}
return tsf;
WARN_ON( i == ATH9K_MAX_TSF_READ );
return (((u64)tsf_upper1 << 32) | tsf_lower);
}
EXPORT_SYMBOL(ath9k_hw_gettsf64);