Hi Dave, On Thu, 23 Apr 2009 09:19:21 +1000, Dave Airlie wrote: > Hi to any i2c people, i2c people tend to live on the linux-i2c list, Cc'd. > So I've been debugging some EDID fetching failures and wanted to ask > about the use of time_after_eq in the i2c bit banging code. > > EDID specification recommends 2ms timeout for the ack on the initial > read, so we set the timeout in our code to usecs_to_jiffies(2200) (10% > margin of error). On my systems this ends up as 1, and we seem to fail > to retrieve EDID one in 10-20 times. Changing the value to 2, always > gets me the EDID I want. > > So looking at drivers/i2c/algos/i2c-algo-bit.c it appears it uses > time_after_eq on jiffies, start + timeout value. So if we have a 10ms > jiffie resolution and enter this at the 9ms point in the 10ms window, > we will seem to exit the loop after 1ms instead of the minimum which I > asked for which is 2.2ms. Should this code use time_after instead of > time_after_eq? Yes, I think it should. This bug has been there pretty much since forever. I suppose people didn't notice because they usually use a large timeout value. Please send a patch fixing this and I'll apply it. -- Jean Delvare -- To unsubscribe from this list: send the line "unsubscribe linux-i2c" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
