linux-kernel - Re: [PATCH v7 1/5] ARM: add basic support for Trusted Foundations

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Date:	Thu, 10 Oct 2013 15:25:46 -0700
From:	Olof Johansson <olof@...om.net>
To:	Stephen Warren <swarren@...dotorg.org>
Cc:	Alexandre Courbot <gnurou@...il.com>,
	Alexandre Courbot <acourbot@...dia.com>,
	Russell King <linux@....linux.org.uk>,
	Tomasz Figa <t.figa@...sung.com>,
	Dave Martin <Dave.Martin@....com>,
	Arnd Bergmann <arnd@...db.de>,
	Kevin Hilman <khilman@...aro.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-tegra@...r.kernel.org" <linux-tegra@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH v7 1/5] ARM: add basic support for Trusted Foundations

On Thu, Oct 10, 2013 at 3:22 PM, Stephen Warren <swarren@...dotorg.org> wrote:
> On 10/10/2013 02:58 PM, Alexandre Courbot wrote:
>> On Wed, Oct 9, 2013 at 4:47 PM, Olof Johansson <olof@...om.net> wrote:
>>> On Fri, Oct 4, 2013 at 9:37 AM, Alexandre Courbot <acourbot@...dia.com> wrote:
> ...
>>> But do we really need to panic here? It's a PITA to debug since it'll
>>> be a very early panic. I'd rather have the system log errors in dmesg
>>> but continue booting with one cpu.
>>
>> Actually the first version of this series continued on one CPU if TF
>> support was missing (as secondary CPUs would simply fail to boot), but
>> IIRC Stephen advocated for the current behavior (panic) instead. I
>> agree such an early panic is hard to debug, especially considering
>> that most devices using TF (Tegra retail devices) do not even feature
>> a serial port.
>>
>> On the other hand, if we continue booting in these conditions the
>> system freezes as soon as cpuidle kicks in, so we won't be going very
>> far anyway. However the console is up when it happens.
>>
>> Maybe if there is a way to disable the kernel features TF is supposed
>> to manage (SMP & cpuidle at the moment) when registration fails, the
>> system could continue more gracefully (even if on one leg) and warn
>> the user about this condition. Stephen, can I have your thoughts on
>> this?
>
> If we can disable the features that rely on TF/secure-mode when support
> is missing, then doing that rather than panic is fine. We do something
> similar for PCIe on Tegra20, where LP2 cpuidle state must be disabled or
> PCIe interrupts won't work.
>
> I would be inclined to merge the patch as-is right now, since it's only
> enabling a new feature that won't see any regressions due to this panic,
> and then add the disable-other-features with a separate patch/series
> later. Does that seem reasonable?

Yes, I tried to make that clear with my initial feedback: I think it
would be good to get away from the panic, but we can merge with it now
and fix it with later patches.


-Olof
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