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

[Scott Wood <oss@buserror.net>]

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@lists.infradead.org>
> > On Behalf Of Scott Wood
> > Sent: 2018年8月31日 1:43
> > To: Vabhav Sharma <vabhav.sharma@nxp.com>;
> > linux-kernel@vger.kernel.org; devicetree@vger.kernel.org;
> > robh+dt@kernel.org; mark.rutland@arm.com;
> > linuxppc-dev@lists.ozlabs.org; linux-arm-kernel@lists.infradead.org;
> > mturquette@baylibre.com; sboyd@kernel.org; rjw@rjwysocki.net;
> > viresh.kumar@linaro.org; linux-clk@vger.kernel.org;
> > linux-pm@vger.kernel.org; linux-kernel-owner@vger.kernel.org;
> > catalin.marinas@arm.com; will.deacon@arm.com;
> > gregkh@linuxfoundation.org; arnd@arndb.de;
> > kstewart@linuxfoundation.org; yamada.masahiro@socionext.com
> > Cc: Yogesh Narayan Gaur <yogeshnarayan.gaur@nxp.com>; Andy Tang
> > <andy.tang@nxp.com>; linux@armlinux.org.uk; Varun Sethi
> > <V.Sethi@nxp.com>; Udit Kumar <udit.kumar@nxp.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