linux-kernel - Re: [PATCH v2 02/16] arm64: dts: add sp804 timer node for Hi6220

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Date:	Mon, 4 Apr 2016 13:21:00 +0200
From:	Linus Walleij <linus.walleij@...aro.org>
To:	Leo Yan <leo.yan@...aro.org>
Cc:	Guodong Xu <guodong.xu@...aro.org>, Xu Wei <xuwei5@...ilicon.com>,
	Mark Rutland <mark.rutland@....com>,
	Rob Herring <robh@...nel.org>,
	Grant Likely <grant.likely@...retlab.ca>,
	Arnd Bergmann <arnd.bergmann@...aro.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	XinWei Kong <kong.kongxinwei@...ilicon.com>
Subject: Re: [PATCH v2 02/16] arm64: dts: add sp804 timer node for Hi6220

On Mon, Apr 4, 2016 at 3:43 AM, Leo Yan <leo.yan@...aro.org> wrote:
> On Sun, Apr 03, 2016 at 09:23:42PM +0200, Linus Walleij wrote:
>> On Sat, Apr 2, 2016 at 11:29 AM, Guodong Xu <guodong.xu@...aro.org> wrote:

>> By chance the code in the driver will allow just one clock and
>> will then assume that both the bus to the timer and the timer
>> itself is clocked from the same clock. But I highly doubt that this
>> is the case.
>
> This patch has been sent out for review previously [1]; So I refered
> other platforms and changed to only enable apb bus clock due I have
> not found timer enabling bits in Hi6220's spec.

This is not about enabling/disabling the clock(s) to the timer.
It doesn't matter if these clocks are always on.

It is about determining the *frequency* of the timers.

It is vital that the timer driver get the right frequency of the clock
to the block from the clock implementation, and I do not think
it is the same as the "apb_pclk".

The thing is that of course "any frequency" will
work but what you will notice is that the timer runs very
weirdly compared to wall-clock time unless the right clock
yielding the right frequency has been specified here.

Yours,
Linus Walleij