linux using usbserial and new board support

[bm16ton]

Hello,
Currently we are using the acm class driver for usb2cdc but this costs us in interrupt endpoints that arent being used. On a lot of f4 devices (most?) only have 4 endpoints so with bmp and uart we loose half of that precious resource to nothing. Usbserial drivers are without a doubt one of if not the simplest drivers to write, in this case take the template and add vid and pid. Tho adding simple functions for flow control and control messages would be recommended and easy enuff to do. Then your done any breaking changes in kernel will be fixed in the driver by whom ever introduced the breaking change. Im really hopeful your open to idea or at least a conversation about its merits. I have more fixes and filling in of missing pieces for sum of the stm32f4 boards, but im not sure if submitting them would be just a headache for boards you mightnot be keen on supporting and i dont want to be a bother. On that subject I have a handful of stm32's mostly f4'sand f7's if any particular models you would like to see support added for please let me know. Thank you for your time and excellent work!
-Ben Maddocks