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Re: [PATCH 6/6] aarch64: Add hp-timing.h
- From: Andrew Pinski <pinskia at gmail dot com>
- To: Marcus Shawcroft <marcus dot shawcroft at gmail dot com>
- Cc: Richard Henderson <rth at twiddle dot net>, Andreas Schwab <schwab at suse dot de>, "libc-alpha at sourceware dot org" <libc-alpha at sourceware dot org>, "azanella at linux dot vnet dot ibm dot com" <azanella at linux dot vnet dot ibm dot com>, "davem at davemloft dot net" <davem at davemloft dot net>, "marcus dot shawcroft at arm dot com" <marcus dot shawcroft at arm dot com>
- Date: Sat, 20 Jun 2015 19:30:17 -0700
- Subject: Re: [PATCH 6/6] aarch64: Add hp-timing.h
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On Tue, Jul 22, 2014 at 2:38 AM, Marcus Shawcroft
<marcus.shawcroft@gmail.com> wrote:
>> On Mon, Jul 21, 2014 at 12:05 PM, Richard Henderson <rth@twiddle.net> wrote:
>
>> Do you know of any real hardware that doesn't have the timers? I really can't
>> imagine them being elided.
>
> I'd like to see the generic timers none optional in cortex-a class
> processors, however they are currently, unfortunately, defined as
> optional. The design choices made in the first few instances of armv8
> hardware are not necessarily a good basis for predicting the variety
> of design choices that will follow in subsequent implementations.
>
>> On 21 July 2014 21:42, Andrew Pinski <pinskia@gmail.com> wrote:
>
>> More than that, right now the Linux kernel requires the timings so it
>> is not optional for the linux kernel.
>> http://lists.infradead.org/pipermail/linux-arm-kernel/2012-August/114155.html
>>
>> That patch makes it sound like it is part of the kernel userland
>> ABI/API as it allows for a fast gettimeofday() (that does not have to
>> be in VDSO if I read the comment correctly).
>
> The counter is for the benefit of the VDSO in order for the VDSO to
> provide a fast gettimeofday on systems where the counter is present.
Can there be a HWCAP that says if virtual timer is available or not then?
Thanks,
Andrew
>
> Cheers
> /Marcus