On Wed, Oct 06, 2010 at 05:52:13PM +0200, Xavier Oswald wrote: > Hi, > > I have a device using the ftdi_sio driver. With a 2.6.32 or 2.6.36 > kernel, this device reacts 2 or 3 times slower as with the 2.6.24 or > 2.6.26 kernel. This is ver annoying. My first think is that It's a > matter of latency or such. What do you think ? What do you mean by "reacts 2 to 3 times slower"? What is your application and setup? > Have you heard anyone having somehow a same problem with latest > kernels ? No, I'm afraid not. > The problem is the same with 2.6.32 and 2.6.36. The device well works > using 2.6.24 and 2.6.26. Does mainline 2.6.32 (i.e. not stable 2.6.32.x) have the same issue? You could run git bisect on 2.6.26..2.6.32 in order to figure what commit caused the change in behaviour your experiencing. > Is it a possibility to change the latency timer when loading the > module or maybe after having it loaded? Yes, you can set the read latency time-out this way: echo 16 > /sys/bus/usb-serial/devices/ttyUSB0/latency_timer where valid latencies are in the range 2..255 ms according to FTDI-documents. For the change to take effect, however, you also need to clear the ASYNC_LOW_LATENCY flag for the port, e.g.: setserial /dev/ttyUSB0 ^low_latency If the low_latency flag is set (which is the default) the lowest possible timeout is used (reported as 1 ms). Consequently, you can only _increase_ the latency this way so this is perhaps not related to your problem. > By the way, when using a serial cable it well works with all kernels > mentioned above. > > I know that it's not very nice to send you a mail directly. I was > wondering if there is an active mailing list or an irc chan related to > ftdi. The one I have found seems deprecated and/or not used anymore. The linux-usb@xxxxxxxxxxxxxxx mailing list is used for all usb-serial drivers. > Thanks a lot. Greetings, Thanks, Johan -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
