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

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Message-ID: <20110420103928.4049573f@lxorguk.ukuu.org.uk>
Date:	Wed, 20 Apr 2011 10:39:28 +0100
From:	Alan Cox <alan@...rguk.ukuu.org.uk>
To:	John Linn <John.Linn@...inx.com>
Cc:	Greg KH <greg@...ah.com>, <linux-kernel@...r.kernel.org>,
	<linux-serial@...r.kernel.org>
Subject: Re: [PATCH] tty/serial: add support for Xilinx PS UART

> Reading up on it a bit as I'm not an expert on it (like you). 
> It's not clear to me what the device driver uses for it's major/minor in
> this case.  

If you don't specify then the kernel picks one. udev can then create the
right /dev/ttyPS1/2/3 nodes itself. If you have devtmpfs enabled then
devtmpfs is a virtual file system which will just have the nodes in at as
specified by the drivers. It eliminates all the hard work maintaining
device nodes/ranges in user space.

> The only reason we didn't just use ttyS0 was that it's not a 8250 really

If you'd attempted to use ttyS0 you would indeed have been told to change
it
> and
> since we have are an FPGA people can add real 8250s in soft logic and
> then
> the system would get confusing.

and that's exactly why !

Alan
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