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Date:	Mon, 15 Sep 2014 12:14:52 -0700
From:	Guenter Roeck <>
To:	James Hogan <>
Cc:	Greg Kroah-Hartman <>,
	Jiri Slaby <>,,
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 <>
> Cc: Greg Kroah-Hartman <>
> Cc: Jiri Slaby <>
> Cc: Guenter Roeck <>

Tested-by: Guenter Roeck <>

Thanks a lot!

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