On Mon, Mar 4, 2019 at 8:27 PM Greg KH <gregkh@xxxxxxxxxxxxxxxxxxx> wrote: > > On Mon, Mar 04, 2019 at 08:19:44PM +0530, Subhashini Rao Beerisetty wrote: > > On Mon, Mar 4, 2019 at 6:53 PM Greg KH <gregkh@xxxxxxxxxxxxxxxxxxx> wrote: > > > > > > On Mon, Mar 04, 2019 at 05:46:54PM +0530, Subhashini Rao Beerisetty wrote: > > > > Hi All, > > > > > > > > > > > > I’ve an UART ports on Xilinx FPGA board and it gets connected to PC > > > > via PCIe bus. I could not find any kernel serial driver which supports > > > > our hardware so I plan to develop a new driver. I see two approaches > > > > to develop an UART driver i.e. either by using tty_register_driver() > > > > or an uart_register_driver(). > > > > > > > > > > > > Regarding my UART module, it has a counter of 16 bits and runs on a > > > > 32Mhz clock. It supports all the standard & non-standard baud’s up to > > > > 4Mbps. > > > > > > What type of UART is it? Odds are it is based on an existing design, no > > > one creates a brand-new UART anymore. Hopefully. If not, what a > > > waste... > > > > For UART type, I see the permitted types are none, 8250, 16450, 16550, > > 16550A, 16650, 16650V2, 16654, 16750, 16850, 16950, and 16954 etc. > > Looking into the data sheet I haven’t found any register or parameter > > defining any of those UART types. Is ‘UART type’ is determined from a > > register settings point of view or a pinout point of view? > > register settings point of view. > > I suggest you do some basic research into how UARTs work before > continuing with this effort, it will save you a lot of time in the end > :) Thanks for you suggestion. I will study on this, I’m glad if you can point some good documentation links on this. > > > > > If I used struct tty_operations, I noticed that baud rate changing is > > > > done via “.set_termios” API, but this method only supports standard > > > > baud rates. I’d like to know why this API does not support > > > > non-standard baud rates? > > > > > > Why do you think it does not? > > From data sheet point of view I'm clear on how to set the non-standard > > baud rate, even I exposed a custom Ioctl for this. But here I’m trying > > to understand how it is achieved by using available UART kernel > > framework. > > For non-standard baud rate requests, observed that > > tty->termios.c_ispeed & tty->termios.c_ospeed set to 38400. I did not > > understood why it changes? > > Have you read the documentation on how to set custom baud rates? I > can't find the link to it at the moment, but it is very possible to do > that today, no special ioctls are needed at all. I think someone was > finally working on getting glibc to support it directly, but I do not > know if those patches ever got merged, so you would just have to "open > code" it in userspace if you want to do this. I could not find clear documentation on this, I’m very much thankful if someone point me on this. I thought of exploring TIOCGSERIAL and TIOCSSERIAL Ioctl’s to set custom baud rates. Now it looks like I should read the kernel code to understand how to achieve this without special ioctls. > > good luck! > > greg k-h
