On Fri, May 24, 2013 at 03:56:37PM +0200, Tobias Winter wrote: > Hi there, > > since my propblem is with usb to serial adapters I was unsure if this is > the right place. If not, please let me know. Not really, linux-usb@ is the proper one, I've included that on the cc: > After equipping a server with a lot of ftdi singleport usb2serial > devices, I ran into a serial device limit that is included in > include/linux/usb/serial.h . > > The limit of devices seems to be 255, resulting in ttyUSB254 to be the > last supported device. > > The codesnippet in question is: > > #define SERIAL_TTY_MINORS 254 /* loads of devices :) */ > #define SERIAL_TTY_NO_MINOR 255 /* No minor was assigned */ Yes, that's the limit of usb-serial devices in the system at the moment. In 10+ years, no one has complained yet, so it's been a good number :) > Output of `lsusb | sort` with 256 usb2serial devices connected: > http://pastebin.com/wqrYUbwZ Nice job. > In case you end up agreeing with me that there are no reasons to limit > the devices to 255, would you be inclined to fix this in the main kernel > tree? Do I have to open up a bug somewhere? You can send a patch making the number dynamic, that would be great to have. > I also tried increasing the numbers further but I run into rollover > issues as the kernel tries to reassign ttyUSB0 ttyUSB1 which is already > taken. It seems without some other modification 256 devices is the limit? Yes, there might be some limits in the tty layer as well for only 256 tty devices, but I haven't looked there in a long time, perhaps that is now no longer the case. > Bus 001 Device 091: ID 0403:6001 Future Technology Devices International, Ltd FT232 USB-Serial (UART) IC I'm just glad to see we can support 91 different devices on a single root hub, that's good to see, as I don't think anyone has tested that in a very long time :) thanks, greg k-h -- To unsubscribe from this list: send the line "unsubscribe linux-serial" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
