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 17:09:04 +0000 [thread overview]
Message-ID: <50D34630.9020708@arm.com> (raw)
In-Reply-To: <20121220.164230.292625215885249791.hdoyu@nvidia.com>
On 20/12/12 14:42, Hiroshi Doyu wrote:
> Marc Zyngier <marc.zyngier@arm•com> wrote @ Thu, 20 Dec 2012 14:32:21 +0100:
>
>> 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).
>
> "tegra114.dtsi" has the folloiwng "tsc" entry. So can we consider that
> if dts has this entry, CNTFRQ is not set, which implies it's in secure
> mode. kernel should set it up by itself? Otherwise, skip this setup
> and use it. For example:
>
> tsc {
> compatible = "nvidia,tegra114-tsc";
> reg = <0x700f0000 0x20000>;
> + setup-cntfrq;
> };
>
> Is this what you explained in the above?
> At least, kernel can survive without bootloader/firmware support, ATM.
No. The DT should only describe the hardware, and not something that is
Linux specific.
Just use the "clock-frequency" attribute in the timer arch-timer node,
and get rid of this CNTFRQ setting. The driver already knows how to deal
with this situation if this attribute is set.
Thanks,
M.
--
Jazz is not dead. It just smells funny...
next prev parent reply other threads:[~2012-12-20 17:09 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
2012-12-20 14:42 ` Hiroshi Doyu
2012-12-20 17:09 ` Marc Zyngier [this message]
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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