Re: Questions regarding adding a patch in linux/drivers/char/8250.c

[Alan Cox <alan@lxorguk.ukuu.org.uk>]

On Mon, 21 May 2012 14:19:34 +0800
"Donald" <donald@asix.com.tw> wrote:

> Hi,
> 
> This is Donald from ASIX Electronics Corp. My company has three PCI to Serial controllers, including MCS9845, MCS9835, and MCS9820.
> Currently those serial devices using these three chips can directly use the Linux kernel's serial driver in
> linux/drivers/char/8250.c. Recently we find these three chips have a hardware bug relating to parity error count function. We have a
> software workaround for this issue. Below for reference is a pseudo code for this workaround.
> 
> serial8250_do_set_termios() {
> 	If ((PID == MCS9845 || PID == MCS935 || PID == MCS9820) && ((termios->c_cflag & PARENB))) {
> 		port->fifosize = 1; /* Change RX FIFO size to 1 byte */
> 		up->ier &= ~UART_IER_RLSI; /* Disable RLSI interrupt */
> 	}	
> }
> 
> Is it possible to add a patch into linux/drivers/char/8250.c for our chips' hardware issue? 

Sure.

The only question I would have is how do we reliably detect the presence
of the UART devices with this erratum. Can we do it from the PCI
identifier ?

Alan