From: marc.zyngier@arm•com (Marc Zyngier)
To: linux-arm-kernel@lists•infradead.org
Subject: [PATCH 5/9] clocksource: tegra: Enable ARM arch_timer with TSC
Date: Thu, 20 Dec 2012 13:32:21 +0000 [thread overview]
Message-ID: <50D31365.9000009@arm.com> (raw)
In-Reply-To: <20121220125507.GB6819@tbergstrom-lnx.Nvidia.com>
On 20/12/12 12:55, Peter De Schrijver wrote:
> On Thu, Dec 20, 2012 at 01:33:42PM +0100, Marc Zyngier wrote:
>> On 20/12/12 12:22, Peter De Schrijver wrote:
>>>>>>> +
>>>>>>> + /* CNTFRQ */
>>>>>>> + asm("mcr p15, 0, %0, c14, c0, 0\n" : : "r" (freq));
>>>>>>> + asm("mrc p15, 0, %0, c14, c0, 0\n" : "=r" (val));
>>>>>>> + BUG_ON(val != freq);
>>>>>>
>>>>>> This is scary. CNTFRQ is only writable from secure mode, and will
>>>>>> explode in any other situation.
>>>>>>
>>>>>> Also, writing to CNTFRQ doesn't change the timer frequency! This is just
>>>>>> a way for secure mode to tell the rest of the world the frequency the
>>>>>> timer is ticking at. Unless you've wired the input clock to be able to
>>>>>> change the frequency?
>>>>>
>>>>> ATM, our upstream kernel is expected in secure mode. This situation
>>>>> may be changed later, though....
>>>>
>>>> I appreciate this. But I expect this kernel to be also used on the
>>>> non-secure side if someone tried to run KVM with it. And this would go
>>>> bang right away.
>>>>
>>>
>>> But the guest wouldn't necessarily have this peripheral, or any other Tegra114
>>> peripheral for that matter?
>>
>> The problem is not so much the guest but the host. The host has to be
>> booted in non-secure, so just saying "we do not support non-secure" is
>> not a very convincing argument.
>>
>> Unless of course you've already decided that you don't want to support
>> KVM on this SoC...
>>
>
> I guess that means we can't support KVM yet. Tegra does not have a secure
> monitor by default. It all depends on what that system integrator does.
VExpress doesn't have a secure monitor either, and yet we run KVM on it
(by switching to non-secure before loading the kernel). Same for Exynos5.
What I'm trying to say is that this code is rather pointless (this
should be done by the firmware/bootloader, not the kernel, or the
information should be provided in DT if CNTFRQ is not set).
This way, no breakage, no dependency on the security level.
M.
--
Jazz is not dead. It just smells funny...
next prev parent reply other threads:[~2012-12-20 13:32 UTC|newest]
Thread overview: 37+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-12-20 9:43 [PATCH 0/9] ARM: Initial support for Tegra 114 SoC Hiroshi Doyu
2012-12-20 9:43 ` [PATCH 1/9] ARM: tegra: fuse: Add chipid TEGRA114 0x35 Hiroshi Doyu
2012-12-20 9:44 ` [PATCH 2/9] HACK: ARM: tegra: Use CLK_IGNORE_UNUSED for Tegra 114 SoC Hiroshi Doyu
2012-12-20 9:44 ` [PATCH 3/9] ARM: tegra: # of CPU cores detection w/ & w/o HAVE_ARM_SCU Hiroshi Doyu
2012-12-20 10:06 ` Felipe Balbi
2012-12-20 11:21 ` Hiroshi Doyu
2012-12-20 18:18 ` Felipe Balbi
2012-12-20 11:17 ` Marc Zyngier
2012-12-20 11:26 ` Hiroshi Doyu
2012-12-20 11:32 ` Marc Zyngier
2012-12-20 9:44 ` [PATCH 4/9] clocksource: tegra: Reorganize funcs by clock functionarities Hiroshi Doyu
2012-12-20 9:44 ` [PATCH 5/9] clocksource: tegra: Enable ARM arch_timer with TSC Hiroshi Doyu
2012-12-20 11:01 ` Marc Zyngier
2012-12-20 11:57 ` Hiroshi Doyu
2012-12-20 12:05 ` Marc Zyngier
2012-12-20 12:22 ` Peter De Schrijver
2012-12-20 12:33 ` Marc Zyngier
2012-12-20 12:55 ` Peter De Schrijver
2012-12-20 13:32 ` Marc Zyngier [this message]
2012-12-20 14:42 ` Hiroshi Doyu
2012-12-20 17:09 ` Marc Zyngier
2012-12-20 22:13 ` Peter De Schrijver
2012-12-20 13:25 ` Hiroshi Doyu
2012-12-20 13:33 ` Marc Zyngier
2012-12-20 9:44 ` [PATCH 6/9] ARM: dt: tegra114: Add new SoC base, Tegra 114 SoC Hiroshi Doyu
2012-12-20 11:27 ` Marc Zyngier
2012-12-29 6:39 ` Olof Johansson
2012-12-31 7:12 ` Hiroshi Doyu
2012-12-20 9:44 ` [PATCH 7/9] ARM: dt: tegra114: Add new board, Dalmore Hiroshi Doyu
2012-12-20 9:44 ` [PATCH 8/9] ARM: dt: tegra114: Add new board, Pluto Hiroshi Doyu
2012-12-20 9:44 ` [PATCH 9/9] ARM: tegra: Add initial support for Tegra 114 SoC Hiroshi Doyu
2013-01-03 16:28 ` Arnd Bergmann
2013-01-04 7:16 ` Hiroshi Doyu
2012-12-24 9:58 ` [PATCH 0/9] ARM: Initial " Mark Zhang
2013-01-03 14:06 ` Hiroshi Doyu
2013-01-03 21:00 ` Thierry Reding
2013-01-03 21:16 ` Stephen Warren
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