On Tue, May 09, 2017 at 11:31:04AM +0200, Anthony Mallet wrote: > On Monday 8 May 2017, at 17:38, Johan Hovold wrote: > > You can read (and also change) the latency-timer value used through > > sysfs: > > > > # cat /sys/bus/usb-serial/devices/ttyUSB0/latency_timer > > 16 > > > > if that's what you needed? But unless you change it, you can infer the > > value to be either 16 (default) or 1 depending on if ASYNC_LOW_LATENCY > > is set as indicated by TIOCGSERIAL. > > Yes, but the sysfs path has a lots a drawbacks: > > - 666 permissions by default, so unprivileged users cannot change it You said you wanted to read it, and an unprivileged user can now again change it through ASYNC_LOW_LATENCY. > - if ASYNC_LOW_LATENCY is not set, the current latency value cannot > be infered (it could have been changed from the default, by e.g. a > udev rule). True, but again you can read it through sysfs also after you (or udev) have changed the default value. > - I don't know any way to guess the sysfs path from a tty device > path, at least not without requiring a lot of extra dependencies > and very linux-specific code. This is all the more complex if you > consider that the tty path can either be a pty, a ftdi_sio tty or > anything else provided that isatty(3) returns 1 ... You can use libudev (or a custom implementation) to find out whether the tty is an FTDI device with the latency_timer sysfs attribute. Yes, this is all both Linux and FTDI specific (the async flags, sysfs, the latency timer, etc). 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
