On Mon, Mar 4, 2019 at 8:27 PM Greg KH <gregkh@linuxfoundation.org> 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@linuxfoundation.org> 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