linux-kernel - RE: [PATCH] tty/serial: add support for Xilinx PS UART

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Date:	Wed, 20 Apr 2011 07:43:29 -0600
From:	John Linn <John.Linn@...inx.com>
To:	Alan Cox <alan@...rguk.ukuu.org.uk>
CC:	<linux-kernel@...r.kernel.org>, <linux-serial@...r.kernel.org>
Subject: RE: [PATCH] tty/serial: add support for Xilinx PS UART

> -----Original Message-----
> From: Alan Cox [mailto:alan@...rguk.ukuu.org.uk]
> Sent: Wednesday, April 20, 2011 3:25 AM
> To: John Linn
> Cc: linux-kernel@...r.kernel.org; linux-serial@...r.kernel.org
> Subject: Re: [PATCH] tty/serial: add support for Xilinx PS UART
> 
> > > > +	/* Min baud rate = 6bps and Max Baud Rate is 10Mbps for
> 100Mhz
> > > clk */
> > > > +	baud = uart_get_baud_rate(port, termios, old, 0,
460800);
> > > > +	xuartps_set_baud_rate(port, baud);
> > >
> > > So why pass 460800 ?
> >
> > Seems like 115200 is better number.
> 
> Well if it can do 10Mbit why not pass 10Mbit as the upper limit ?

The only reason would be because we don't test it, but yes that could be
done.

> 
> > > And set the baud rate (see 8250.c for an example). Note that the
> > helper
> > > functions know about mapping slight errors so if you are asked for
> > 9600
> > > and the hardware does 9575 it will report B9600 as you'd expect
not
> do
> > > something crazy.
> > >
> >
> > Sorry I didn't follow what you meant above. The h/w is a bit
> different
> > with it's
> > baud rate settings due to 2 different dividers.
> 
> After you've worked out what baud rate you actually set do
> 
> 	       /* Don't rewrite B0 */
>         if (tty_termios_baud_rate(termios))
>                 tty_termios_encode_baud_rate(termios, baud, baud);
> 
> 
> which will ensure that the termios reflects the actual rate.

Thanks for clarifying, I'll look at that.

-- John

> 
> Alan


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