linux-kernel - Re: [PATCH v2 1/2] devicetree: add binding for generic mmio clocksource

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Date:	Fri, 09 Oct 2015 17:19:40 +0100
From:	Måns Rullgård <mans@...sr.com>
To:	Rob Herring <robherring2@...il.com>
Cc:	Mark Rutland <mark.rutland@....com>,
	Rob Herring <robh+dt@...nel.org>,
	Pawel Moll <pawel.moll@....com>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	Kumar Gala <galak@...eaurora.org>,
	"devicetree\@vger.kernel.org" <devicetree@...r.kernel.org>,
	"linux-kernel\@vger.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 1/2] devicetree: add binding for generic mmio clocksource

Måns Rullgård <mans@...sr.com> writes:

> Rob Herring <robherring2@...il.com> writes:
>
>> On Wed, Oct 7, 2015 at 11:47 AM, Måns Rullgård <mans@...sr.com> wrote:
>>> What would be a proper way to select a sched_clock source?  I realise
>>> it's a Linux-specific thing and DT is supposed to be generic, but the
>>> information must be provided somehow.
>>
>> The kernel already has some logic to do this. Most number of bits
>> followed by highest frequency will be the winning sched_clock. You
>> might also want to look at things like always on or not.
>
> The problem is that sched_clock_register() doesn't take a pointer to be
> passed back to the read_sched_clock callback like most interfaces of
> this type do.  This means the callback must use global variables set up
> before the register call, but at that time there's no way of knowing
> which one will be used.  If there were a way of getting a pointer to the
> callback, it would be a simple matter of registering all instances and
> letting the kernel choose which to use.

Anyone got a comment on this?  Do I have to send a patch adding this
before anyone will tell me why it's a bad idea?  (That method almost
always works.)

-- 
Måns Rullgård
mans@...sr.com
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