linux-kernel - Re: [PATCH] tty/metag_da: Add console

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Message-ID: <20140915191452.GA18175@roeck-us.net>
Date:	Mon, 15 Sep 2014 12:14:52 -0700
From:	Guenter Roeck <linux@...ck-us.net>
To:	James Hogan <james.hogan@...tec.com>
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Jiri Slaby <jslaby@...e.cz>, linux-kernel@...r.kernel.org,
	linux-metag@...r.kernel.org
Subject: Re: [PATCH] tty/metag_da: Add console_poll module parameter

On Fri, Sep 12, 2014 at 11:15:22PM +0100, James Hogan wrote:
> Currently the metag_da console channel is write only, it doesn't get
> polled for incoming data. This is for performance & latency reasons as
> polling blocks the processor for a significant amount of time waiting
> for the JTAG probe to respond to the request and restart the thread.
> This means that the console channel cannot be used for a login prompt,
> so ttyDA2 is usually used instead.
> 
> In a virtual environment with a virtual DA such as QEMU however the
> polling is much cheaper as the request can be handled immediately. It is
> useful to be able to enable polling in such an environment in order to
> get both the kernel log and a usable login prompt on the same DA
> channel.
> 
> Add a console_poll module parameter which allows polling to be enabled
> for the console channel. It defaults to off as that is the current
> behaviour for good reason on real hardware.
> 
> It can be enabled by appending metag_da.console_poll to the kernel
> command line.
> 
> Signed-off-by: James Hogan <james.hogan@...tec.com>
> Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
> Cc: Jiri Slaby <jslaby@...e.cz>
> Cc: Guenter Roeck <linux@...ck-us.net>

Tested-by: Guenter Roeck <linux@...ck-us.net>

Thanks a lot!

Guenter
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