linux-kernel - Re: [PATCH 3/5] drivers: clk-qoriq: Add clockgen support for lx2160a

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Message-ID: <f6707cb54c3e6da1b50f45f915c996dfccfeacda.camel@buserror.net>
Date:   Fri, 31 Aug 2018 15:28:44 -0500
From:   Scott Wood <oss@...error.net>
To:     Andy Tang <andy.tang@....com>,
        Vabhav Sharma <vabhav.sharma@....com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "robh+dt@...nel.org" <robh+dt@...nel.org>,
        "mark.rutland@....com" <mark.rutland@....com>,
        "linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "mturquette@...libre.com" <mturquette@...libre.com>,
        "sboyd@...nel.org" <sboyd@...nel.org>,
        "rjw@...ysocki.net" <rjw@...ysocki.net>,
        "viresh.kumar@...aro.org" <viresh.kumar@...aro.org>,
        "linux-clk@...r.kernel.org" <linux-clk@...r.kernel.org>,
        "linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
        "linux-kernel-owner@...r.kernel.org" 
        <linux-kernel-owner@...r.kernel.org>,
        "catalin.marinas@....com" <catalin.marinas@....com>,
        "will.deacon@....com" <will.deacon@....com>,
        "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
        "arnd@...db.de" <arnd@...db.de>,
        "kstewart@...uxfoundation.org" <kstewart@...uxfoundation.org>,
        "yamada.masahiro@...ionext.com" <yamada.masahiro@...ionext.com>
Cc:     Yogesh Narayan Gaur <yogeshnarayan.gaur@....com>,
        "linux@...linux.org.uk" <linux@...linux.org.uk>,
        Varun Sethi <V.Sethi@....com>, Udit Kumar <udit.kumar@....com>
Subject: Re: [PATCH 3/5] drivers: clk-qoriq: Add clockgen support for lx2160a

On Fri, 2018-08-31 at 06:12 +0000, Andy Tang wrote:
> Hi Scott,
> 
> Please see my replay inline.
> 
> > -----Original Message-----
> > From: linux-arm-kernel <linux-arm-kernel-bounces@...ts.infradead.org>
> > On Behalf Of Scott Wood
> > Sent: 2018年8月31日 1:43
> > To: Vabhav Sharma <vabhav.sharma@....com>;
> > linux-kernel@...r.kernel.org; devicetree@...r.kernel.org;
> > robh+dt@...nel.org; mark.rutland@....com;
> > linuxppc-dev@...ts.ozlabs.org; linux-arm-kernel@...ts.infradead.org;
> > mturquette@...libre.com; sboyd@...nel.org; rjw@...ysocki.net;
> > viresh.kumar@...aro.org; linux-clk@...r.kernel.org;
> > linux-pm@...r.kernel.org; linux-kernel-owner@...r.kernel.org;
> > catalin.marinas@....com; will.deacon@....com;
> > gregkh@...uxfoundation.org; arnd@...db.de;
> > kstewart@...uxfoundation.org; yamada.masahiro@...ionext.com
> > Cc: Yogesh Narayan Gaur <yogeshnarayan.gaur@....com>; Andy Tang
> > <andy.tang@....com>; linux@...linux.org.uk; Varun Sethi
> > <V.Sethi@....com>; Udit Kumar <udit.kumar@....com>
> > Subject: Re: [PATCH 3/5] drivers: clk-qoriq: Add clockgen support for
> > lx2160a
> > 
> > On Thu, 2018-08-30 at 12:39 -0500, Scott Wood wrote:
> > > On Thu, 2018-08-30 at 07:36 +0000, Vabhav Sharma wrote:
> > > > > 
> > > > > Why are you increasing NUM_CMUX beyond 8 for a chip that only
> > 
> > has
> > > > > 8 entries in cmux_to_group?
> > > > 
> > > > Configuration is 16 cores,8 cluster with 2 cores in each cluster
> > > 
> > > So?  This is about cmuxes, not cores.  You're increasing the array
> > > without ever using the new size.
> > 
> > Oh, and you also broke p4080 which has 8 cmuxes but no -1 terminator,
> > because the array was of length 8.  Probably the array should be changed
> > to NUM_CMUX+1 so every array can be -1 terminated.
> > 
> 
> [Andy] How about we add -1 terminator to p4080 and increase NUM_CMUX to 16?

Why 16?  What does such a change have to do with this chip, which according to
the rest of the patch has 8 cmuxes?

> We don't want to increase NUM_CMUX each time new soc with more cmuxes added.

You don't want to have to make a trivial change each time you exceed a limit
that has yet to be exceeded once since NUM_CMUX was added?  This isn't ABI or
in any other way hard to change.  It's right in the same file as the chip
description you'd be adding.

And even if a chip did come along with 16 cmuxes, you'd then need to increase
the array to 17 to hold the -1 if you don't want to leave a situation like the
p4080 is in now, where a chip's cmux array could be broken by increasing
NUM_CMUX further.

-Scott