From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1759126AbbJISqh (ORCPT ); Fri, 9 Oct 2015 14:46:37 -0400 Received: from smtp.codeaurora.org ([198.145.29.96]:59821 "EHLO smtp.codeaurora.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756337AbbJISqf (ORCPT ); Fri, 9 Oct 2015 14:46:35 -0400 Date: Fri, 9 Oct 2015 11:46:32 -0700 From: Stephen Boyd To: Rob Herring Cc: =?iso-8859-1?Q?M=E5ns_Rullg=E5rd?= , Mark Rutland , Pawel Moll , Ian Campbell , Kumar Gala , "devicetree@vger.kernel.org" , "linux-kernel@vger.kernel.org" Subject: Re: [PATCH v2 1/2] devicetree: add binding for generic mmio clocksource Message-ID: <20151009184632.GR26883@codeaurora.org> References: <1444232234-2133-1-git-send-email-mans@mansr.com> <20151007154727.GC28981@leverpostej> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 10/09, Rob Herring wrote: > +Stephen who has worked on this code. > > On Fri, Oct 9, 2015 at 11:19 AM, Måns Rullgård wrote: > > Måns Rullgård writes: > > > >> Rob Herring writes: > >> > >>> On Wed, Oct 7, 2015 at 11:47 AM, Måns Rullgård 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. > Does that mean a flag day? Urgh. Pain. I'm not opposed to adding a pointer, in fact it might be better for performance so that we don't take a cache miss in read() functions that need to load some pointer. We were talking about that problem a few months ago, but nothing came of it. -- Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, a Linux Foundation Collaborative Project