linux-kernel - Re: [PATCH 1/3] hvc_dcc: bind driver to core0 for reads and writes

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Date:	Tue, 30 Jun 2015 14:58:15 +0100
From:	Will Deacon <will.deacon@....com>
To:	Timur Tabi <timur@...eaurora.org>
Cc:	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Shanker Donthineni <shankerd@...eaurora.org>,
	"awallis@...eaurora.org" <awallis@...eaurora.org>,
	"abhimany@...eaurora.org" <abhimany@...eaurora.org>,
	"sboyd@...eaurora.org" <sboyd@...eaurora.org>,
	Vipul Gandhi <vgandhi@...eaurora.org>
Subject: Re: [PATCH 1/3] hvc_dcc: bind driver to core0 for reads and writes

On Fri, Jun 26, 2015 at 07:52:34PM +0100, Timur Tabi wrote:
> Some debuggers, such as Trace32 from Lauterbach GmbH, do not handle
> reads/writes from/to DCC on secondary cores.  Each core has its
> own DCC device registers, so when a core reads or writes from/to DCC,
> it only accesses its own DCC device.  Since kernel code can run on
> any core, every time the kernel wants to write to the console, it
> might write to a different DCC.
> 
> In SMP mode, Trace32 only uses the DCC on core 0.  In AMP mode, it
> creates multiple windows, and each window shows the DCC output
> only from that core's DCC.  The result is that console output is
> either lost or scattered across windows.
> 
> Selecting this option will enable code that serializes all console
> input and output to core 0.  The DCC driver will create input and
> output FIFOs that all cores will use.  Reads and writes from/to DCC
> are handled by a workqueue that runs only core 0.

What happens if CPU0 is hotplugged off?

Will
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