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

[Andy Tang]

Hi Scott,

Please see my replay inline.

> -----Original Message-----
> From: linux-arm-kernel <linux-arm-kernel-bounces@xxxxxxxxxxxxxxxxxxx>
> On Behalf Of Scott Wood
> Sent: 2018å9æ4æ 4:34
> To: Andy Tang <andy.tang@xxxxxxx>; Vabhav Sharma
> <vabhav.sharma@xxxxxxx>; linux-kernel@xxxxxxxxxxxxxxx;
> devicetree@xxxxxxxxxxxxxxx; robh+dt@xxxxxxxxxx;
> mark.rutland@xxxxxxx; linuxppc-dev@xxxxxxxxxxxxxxxx;
> linux-arm-kernel@xxxxxxxxxxxxxxxxxxx; mturquette@xxxxxxxxxxxx;
> sboyd@xxxxxxxxxx; rjw@xxxxxxxxxxxxx; viresh.kumar@xxxxxxxxxx;
> linux-clk@xxxxxxxxxxxxxxx; linux-pm@xxxxxxxxxxxxxxx;
> linux-kernel-owner@xxxxxxxxxxxxxxx; catalin.marinas@xxxxxxx;
> will.deacon@xxxxxxx; gregkh@xxxxxxxxxxxxxxxxxxx; arnd@xxxxxxxx;
> kstewart@xxxxxxxxxxxxxxxxxxx; yamada.masahiro@xxxxxxxxxxxxx
> Cc: Yogesh Narayan Gaur <yogeshnarayan.gaur@xxxxxxx>;
> linux@xxxxxxxxxxxxxxx; Varun Sethi <V.Sethi@xxxxxxx>; Udit Kumar
> <udit.kumar@xxxxxxx>
> Subject: Re: [PATCH 3/5] drivers: clk-qoriq: Add clockgen support for
> lx2160a
> 
> On Mon, 2018-09-03 at 01:17 +0000, Andy Tang wrote:
> > Hi Scott,
> >
> > Please see my replay in line.
> >
> > > -----Original Message-----
> > > From: Linuxppc-dev
> > > <linuxppc-dev-bounces+b29983=freescale.com@xxxxxxxxxxxxxxxx> On
> > > Behalf Of Scott Wood
> > > Sent: 2018å9æ1æ 4:29
> > > To: Andy Tang <andy.tang@xxxxxxx>; Vabhav Sharma
> > > <vabhav.sharma@xxxxxxx>; linux-kernel@xxxxxxxxxxxxxxx;
> > > devicetree@xxxxxxxxxxxxxxx; robh+dt@xxxxxxxxxx;
> > > mark.rutland@xxxxxxx; linuxppc-dev@xxxxxxxxxxxxxxxx;
> > > linux-arm-kernel@xxxxxxxxxxxxxxxxxxx; mturquette@xxxxxxxxxxxx;
> > > sboyd@xxxxxxxxxx; rjw@xxxxxxxxxxxxx; viresh.kumar@xxxxxxxxxx;
> > > linux-clk@xxxxxxxxxxxxxxx; linux-pm@xxxxxxxxxxxxxxx;
> > > linux-kernel-owner@xxxxxxxxxxxxxxx; catalin.marinas@xxxxxxx;
> > > will.deacon@xxxxxxx; gregkh@xxxxxxxxxxxxxxxxxxx; arnd@xxxxxxxx;
> > > kstewart@xxxxxxxxxxxxxxxxxxx; yamada.masahiro@xxxxxxxxxxxxx
> > > Cc: Yogesh Narayan Gaur <yogeshnarayan.gaur@xxxxxxx>;
> > > linux@xxxxxxxxxxxxxxx; Udit Kumar <udit.kumar@xxxxxxx>; Varun
> Sethi
> > > <V.Sethi@xxxxxxx>
> > > 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:
> > > > 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.
> > >
> >
> > [Andy] Adding buffer to a limitation number is always a good habit
> > when coding. We often forget to increase this value when a new chip
> > with more cmuxes added.
> 
> "often"?  There has never been a new chip added with more cmuxes
> than p4080's 8, and if one does come along and you forget, the compiler
> should complain about exceeding the array length with a static initializer.
> This isn't like an array that is filled with a runtime-determined length.
> 
> > Like this patch, we didn't increase this value at first. We spent a
> > lot of time finding out that NUM_CMUX needs to be increased too.
> 
> Are you talking about some other chip that you haven't sent a patch for
> yet?
> Or is the cmux array for this chip wrong?  What specifically did you see
> happen "at first"?
> 
[Andy] Sorry, "Often" is not a right word. I meant we tend to add new soc without updating NUM_CMUX.
 
> > It is a personal preference how to set this value. I think it is
> > better to increase it to 16, not NUM_CMUX+1 as long as we fix the
> > P4080 issue even though it is a trivial change. And I agree the
> > description needs to be updated.
> 
> I'm not the clock maintainer, so it's not up to me, but I don't see the point
> in setting it to an arbitrary number, and I do not agree that increasing
> NUM_CMUX is a suitable replacement for NUM_CMUX+1 in
> cmux_to_group[], as that array should be one larger than cmux[] in order
> to allow every chip to have a
> -1 terminator.  In any case, any change to NUM_CMUX should be a
> separate patch because it's not required for lx2160a support (assuming
> lx2160a was correctly described by this patch).
[Andy] I don't see any impropriate about your suggestion. so we are going to do in your way.

Thanks,
Andy
> 
> -Scott
> 
> 
> 
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