Re: [PATCH] ath9k: fix TSF after reset on AR913x

[Felix Fietkau <nbd@openwrt.org>]

On 2010-07-01 8:39 AM, Johannes Berg wrote:
> On Thu, 2010-07-01 at 02:47 +0200, Felix Fietkau wrote:
> 
>> No, the TSF value at this point is not accurate. It differs
>> semi-randomly by a few orders of magnitude from the time measured by the
>> CPU timer. The value I put in above is just an approximation, but since
>> making it completely accurate is impossible, I figured this is good
>> enough, especially since the value will most likely not deviate much
>> from what I've measured here.
> 
> Are you sure it doesn't depend on CPU speed as well since the driver is
> involved here? Or DMA speed?
Yes, it depends on CPU speed, but there's not a lot of variation
possible, because this only affects one, maybe two different SoC types
with similar CPU speed, and a large part of the delay is probably
constant because of udelay calls.
As I said, being precise here is impossible anyway, this is only a
workaround for a hw issue, and this simple approximation should not
cause any problems for anything. Even if the AP's TSF jumps by a few
microseconds, the clients will catch on to that pretty quickly.

- Felix