From: slash.tmp@free•fr (Mason)
To: linux-arm-kernel@lists•infradead.org
Subject: Dropping "depends on SMP" for HAVE_ARM_TWD -- take 2
Date: Sat, 3 Oct 2015 11:49:41 +0200 [thread overview]
Message-ID: <560FA4B5.1040709@free.fr> (raw)
In-Reply-To: <20151003103219.1e10bdeb@arm.com>
On 03/10/2015 11:32, Marc Zyngier wrote:
> On Sat, 3 Oct 2015 00:34:02 +0100
> M?ns Rullg?rd wrote:
>> Mason writes:
>>
>>> My port requires the TWD to function. So I'm using
>>> select HAVE_ARM_TWD (no "if SMP") to have it work
>>> even on MULTIPLATFORM UP configs.
>>
>> You could just let it use another timer in the non-smp case if you
>> didn't have that weird aversion towards using my code.
>
> I have no idea what your code does, but using the timer that is
> integrated into the core (just like on any other A9 implementation)
> feels like the right thing to do, unless the HW is too broken to use
> TWD.
>
> Another timer is a nice thing to have (it probably comes in handy for
> suspend/resume, and it may have a much better resolution), but this
> seems like icing on the cake at this point. Let's see the cake first.
Marc,
I have a quick question for you :-)
As I stated several months ago, my goal is to produce the simplest
port possible, which is why I chose the TWD instead of platform
timers. At one point, I was also considering the global timer.
(I have a Cortex A9 MPCore.) But as far as I could tell, the
code for the global timer does not handle CPU frequency changes
(while smp_twd.c does), is that correct?
AFAIU, TWD timers and global timer "tick" at the frequency of
PERIPHCLK (which is CPUCLK/2 in my implementation). Therefore,
code needs to be specifically written to handle cpufreq events.
Is that a correct understanding?
As for you comment about resolution, nominal PERIPHCLK is 600 MHz.
Hard to beat that kind of resolution, I think.
Have a nice week end.
Regards.
next prev parent reply other threads:[~2015-10-03 9:49 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-10-02 9:52 Dropping "depends on SMP" for HAVE_ARM_TWD -- take 2 Mason
2015-10-02 13:24 ` Mason
2015-10-02 18:02 ` Stephen Boyd
2015-10-02 18:48 ` Felipe Balbi
2015-10-02 18:55 ` Russell King - ARM Linux
2015-10-02 19:18 ` Felipe Balbi
2015-10-02 18:50 ` Mason
2015-10-02 19:41 ` Stephen Boyd
2015-10-02 23:34 ` Måns Rullgård
2015-10-03 9:32 ` Marc Zyngier
2015-10-03 9:49 ` Mason [this message]
2015-10-03 10:12 ` Marc Zyngier
2015-10-05 5:46 ` Sören Brinkmann
2015-10-05 7:38 ` Mason
2015-10-05 9:03 ` Linus Walleij
2015-10-05 11:49 ` Afzal Mohammed
2015-10-05 15:13 ` Sören Brinkmann
2015-10-05 15:25 ` Russell King - ARM Linux
2015-10-06 8:21 ` Mason
2015-10-06 19:38 ` Stephen Boyd
2015-10-06 20:01 ` Felipe Balbi
2015-10-06 20:17 ` Mason
2015-10-06 21:05 ` Felipe Balbi
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