RE: [PATCH] clk: clk-fixed-factor: Use new macro CLK_OF_DECLARE_DRIVER

[Rajan Vaja <RAJANV@xilinx.com>]

Hi Stephen,

> -----Original Message-----
> From: Rajan Vaja
> Sent: 16 March 2018 05:20 PM
> To: 'Stephen Boyd' <sboyd@kernel.org>
> Cc: linux-clk@vger.kernel.org; linux-kernel@vger.kernel.org; Jolly Shah
> <JOLLYS@xilinx.com>; Michal Simek <michals@xilinx.com>;
> mturquette@baylibre.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@kernel.org]
> > Sent: 16 March 2018 12:17 AM
> > To: Rajan Vaja <RAJANV@xilinx.com>
> > Cc: linux-clk@vger.kernel.org; linux-kernel@vger.kernel.org; Jolly Shah
> > <JOLLYS@xilinx.com>; Michal Simek <michals@xilinx.com>;
> > mturquette@baylibre.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@kernel.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.
[Rajan] Any comments on this?
Unless we have proper solution ready, we need to have some mechanism to handle this scenario.
clock-output-names is optional and without this, it mandates to use clock-output-names.

> 
> >
> > 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.