linux-kernel - Re: [RFC PATCH 1/7] serial: Emulate break using control characters

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Date:	Mon, 23 Mar 2015 19:05:11 +0000
From:	One Thousand Gnomes <gnomes@...rguk.ukuu.org.uk>
To:	Dave Martin <Dave.Martin@....com>
Cc:	Daniel Thompson <daniel.thompson@...aro.org>,
	linaro-kernel@...ts.linaro.org, patches@...aro.org,
	Marc Zyngier <marc.zyngier@....com>,
	Catalin Marinas <catalin.marinas@....com>,
	Will Deacon <will.deacon@....com>,
	linux-kernel@...r.kernel.org, John Stultz <john.stultz@...aro.org>,
	Andrew Thoelke <andrew.thoelke@....com>,
	Sumit Semwal <sumit.semwal@...aro.org>,
	linux-arm-kernel@...ts.infradead.org
Subject: Re: [RFC PATCH 1/7] serial: Emulate break using control characters

> > To be clear I included the patch in this series only because:
> > 
> > 1. I couldn't figure out any way to send a serial break to the ARM
> >    Foundation Model making it impossible for me to provoke SysRq actions
> >    from interrupt context,
> 
> Agreed, there's no direct way to do it (annoyingly).
> 
> Arguably that's a deficiency in the model, though that's not much help to
> you right now.

If it isn't affecting real hardware and it's just for a flawed model then
hack a check for a suitable symbol into the specific patches for
the model and its serial driver and claim it was a break - don't dump it
into the mainstream.

There are some "conventional" escapes platforms have used (ctrl and
symbols for example such as ctrl-^) which are less likely to cause
conflicts than sequences. Nevetheless its not something you want anywhere
mainstream if you can avoid it because those symbols could be sent over a
remote management modem or similar.

They may be better if it does need to end up in the core kernel.

Alan
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