linux-kernel - RE: [PATCH] clk: clk-fixed-factor: Use new macro CLK_OF_DECLARE

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Date:   Fri, 16 Mar 2018 11:49:37 +0000
From:   Rajan Vaja <RAJANV@...inx.com>
To:     Stephen Boyd <sboyd@...nel.org>
CC:     "linux-clk@...r.kernel.org" <linux-clk@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Jolly Shah <JOLLYS@...inx.com>,
        Michal Simek <michals@...inx.com>,
        "mturquette@...libre.com" <mturquette@...libre.com>
Subject: RE: [PATCH] clk: clk-fixed-factor: Use new macro
 CLK_OF_DECLARE_DRIVER

Hi Stephen,

Thanks for the comment.

> -----Original Message-----
> From: Stephen Boyd [mailto:sboyd@...nel.org]
> Sent: 16 March 2018 12:17 AM
> To: Rajan Vaja <RAJANV@...inx.com>
> Cc: linux-clk@...r.kernel.org; linux-kernel@...r.kernel.org; Jolly Shah
> <JOLLYS@...inx.com>; Michal Simek <michals@...inx.com>;
> mturquette@...libre.com
> Subject: RE: [PATCH] clk: clk-fixed-factor: Use new macro
> CLK_OF_DECLARE_DRIVER
> 
> Quoting Rajan Vaja (2018-03-09 11:27:40)
> > > From: Stephen Boyd [mailto:sboyd@...nel.org]
> > >
> > > Is the intent to register the clk twice? I believe things are working as
> > > intended without this patch, so maybe you can explain a little more what
> > > you're trying to fix.
> > [Rajan] Yes. During of_clk_init() if some DT fixed factor clock has
> > parent which is neither mentioned in output-clock-names of clock
> > controller nor registered as clock provider, of_clk_init() will try to
> > forcefully register in second loop.
> >
> >                         if (force || parent_ready(clk_provider->np)) {
> >
> >                                 /* Don't populate platform devices */
> >                                 of_node_set_flag(clk_provider->np,
> >                                                  OF_POPULATED);
> >
> > So registration of this DT fixed-factor clock would fail as parent
> > would be NULL as below (called from _of_fixed_factor_clk_setup()):
> > parent_name = of_clk_get_parent_name(node, 0);
> >
> > On the other hand, even if registration failed, that node will be
> > marked as OF_POPULATED, so probe of clk-fixed-factor.c will also not
> > be called and that DT fixed-factor clock would never be registered.
> >
> > Same thing is discussed at  https://lkml.org/lkml/2017/6/5/681 .
> 
> Ok. I believe the answer is to fix the DT to describe the parent chain
> properly with clock-output-names. Otherwise, we have no good way of
> figuring out what the name should be.
[Rajan] clock DT binding doc says that clock-output-names property
is optional and sometimes not recommended. 
I think this patch fixes the issue we have which mandates to add clock-output-names
property (for this particular case). Also, IIUC platform driver probe in clk-fixed-factor.c
will never be called unless we use CLK_OF_DECLARE_DRIVER.
I completely agree that proper solution would be to stop using strings to
describe clock topology.

> 
> The alternative is to start working on a solution for having the clk
> framework stop using strings to describe clk topology. My plan there is
> to allow clk registration to indicate that another parent names array
> should be used with clk_get() of the device or node pointer that's
> associated with the clk during registration to find the parent . If we
> had that, then we could hook up clks into the tree by calling clk_get()
> in the framework and map through the clock-names property. This also
> gets us to a point where clk names don't have to be globally unique,
> which would be nice.