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Subject: RE: [PATCH] tty/serial: add support for Xilinx PS UART
Date: Wed, 20 Apr 2011 07:43:29 -0600
In-Reply-To: <20110420102501.1e395f14@lxorguk.ukuu.org.uk>
Thread-Topic: [PATCH] tty/serial: add support for Xilinx PS UART
Thread-Index: Acv/PLPOl8sNLEFuS8uTsbXQH/yfoQAI/x0A
References: <e35578a9-909d-4594-bbe4-41d89b5f9b3e@VA3EHSMHS014.ehs.local><20110419221530.7370d013@lxorguk.ukuu.org.uk><551928f1-72b8-432e-879e-8721b5c87414@VA3EHSMHS017.ehs.local> <20110420102501.1e395f14@lxorguk.ukuu.org.uk>
From: John Linn <John.Linn@xilinx.com>
To: Alan Cox <alan@lxorguk.ukuu.org.uk>
CC: <linux-kernel@vger.kernel.org>, <linux-serial@vger.kernel.org>
Message-ID: <b744d309-dbb5-44d4-9d51-98e50970c2a2@VA3EHSMHS018.ehs.local>
Sender: linux-kernel-owner@vger.kernel.org
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> -----Original Message-----
> From: Alan Cox [mailto:alan@lxorguk.ukuu.org.uk]
> Sent: Wednesday, April 20, 2011 3:25 AM
> To: John Linn
> Cc: linux-kernel@vger.kernel.org; linux-serial@vger.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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