linux-kernel - RE: [Question] Ask for arm arch timer

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Date:	Wed, 16 Oct 2013 18:25:43 -0700
From:	Neil Zhang <zhangwm@...vell.com>
To:	Catalin Marinas <catalin.marinas@....com>,
	Rob Herring <robherring2@...il.com>
CC:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Yu Tang <ytang5@...vell.com>, Zhou Zhu <zzhu3@...vell.com>,
	Will Deacon <Will.Deacon@....com>
Subject: RE: [Question] Ask for arm arch timer

> -----Original Message-----
> From: Catalin Marinas [mailto:catalin.marinas@....com]
> Sent: 2013年10月16日 21:21
> To: Rob Herring
> Cc: Neil Zhang; linux-kernel@...r.kernel.org; Yu Tang; Zhou Zhu; Will Deacon
> Subject: Re: [Question] Ask for arm arch timer
> 
> On Wed, Oct 16, 2013 at 01:59:25PM +0100, Rob Herring wrote:
> > On 10/16/2013 07:39 AM, Neil Zhang wrote:
> > > I saw your following patch called clocksource_of_init() directly in
> > > time_init() for arm64.
> > > My question is that what should we do if there are some Soc special
> > > work need to be done before arch timer can be used?
> > > Thanks in advance.
> >
> > If the timer itself is different, then you should have a different DT
> > compatible string which you can use to trigger additional initialization.
> >
> > Integration level initialization like enabling clocks would need
> > something different as no machine descriptors exist for arm64.
> >
> > Another option would be do the setup in secure world or the bootloader.
> 
> The generic timer should indeed be initialised in the firmware (bootloader may
> not be suitable if initialisation needs to happen on each CPU). Linux doesn't need
> to do other things than reading the frequency, programming the interrupts,
> counters (but definitely not SoC-specific initialisation).
> 
> > Can you be more specific what initialization is needed.
> 
> I'm interested in this as well.

Thanks Catalin and Rob!
Yes, we need to select the clk source and enable it.
Seems we need to put more and more works into firmware on arm64.

> 
> --
> Catalin

Best Regards,
Neil Zhang