Hi Vivien, On Fri, Jul 10, 2015 at 02:20:47PM -0400, Vivien Didelot wrote: > > > > is this really beneficial and/or needed ? > > Except using existing generic code, no. > > > It adds at least 1ms delay to a loop which did not have any delay at > > all unless the register read itself was sleeping. > > I must have missed where is the benefit from spin reading 10 times this > register, rather than sleeping 1ms between tests. Does this busy bit > behaves differently from the phy, atu, scratch, or vtu busy bits? > Benefit is reaction time, mostly. If the result isn't ready after the first spin, the new code path adds a mandatory 1-2ms delay. This could add up to a lot if that kind of retry is seen a lot.
I don't now if there is a specific time limit for this busy bit, and/or if it behaves differently than the others in terms of timing. > > Is the original function seen to return a timeout error under some > > circumstances ? > > I didn't experience it myself, but I guess it may happen. In addition to > that, the current implementation doesn't check eventual read error. > That's why I saw a benefit in using _mv88e6xxx_wait(). Checking for a read error (or a timeout) is definitely a good thing. I could also imagine that, for example, a "clear statistics" request takes more time than currently supported. This is why I asked if you had seen a timeout with the old code. Personally I'd rather leave the wait loop alone and only introduce error checking unless there is a reason to introduce a sleep, but I'd like to hear Andrew's and/or Florian's opinion. Thanks, Guenter -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
