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

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Date:	Fri, 9 Oct 2015 12:53:17 -0500
From:	Rob Herring <robherring2@...il.com>
To:	Måns Rullgård <mans@...sr.com>,
	Stephen Boyd <sboyd@...eaurora.org>
Cc:	Mark Rutland <mark.rutland@....com>,
	Pawel Moll <pawel.moll@....com>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	Kumar Gala <galak@...eaurora.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 1/2] devicetree: add binding for generic mmio clocksource

+Stephen who has worked on this code.

On Fri, Oct 9, 2015 at 11:19 AM, Måns Rullgård <mans@...sr.com> wrote:
> 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.)

Adding a ptr to the callback seems fine to me.

Rob
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