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: 04 June 2018 09:11 AM
> 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 reply.
> 
> > -----Original Message-----
> > From: Stephen Boyd [mailto:sboyd@kernel.org]
> > Sent: 02 June 2018 12:11 PM
> > 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 (2018-05-03 02:18:30)
> > > 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.
> > >
> >
> > I couldn't read your outlook sent email and I was too busy to go
> > translate it. Some bug in my MUA it seems.
> >
> > Can you add the output-names property? In this case it's practically
> > mandatory, so if you can't do it I'd like to hear why not.
> [Rajan] In our case, we are firmware maintains clock database and driver query
> clocks
> from firmware and registers clock based on information received from
> firmware. So
> output clock names are not fixed.
> https://patchwork.kernel.org/patch/10439893/ - dt-bindings: clock: Add
> bindings for ZynqMP clock driver
> https://patchwork.kernel.org/patch/10439891/ - drivers: clk: Add ZynqMP
> clock driver
[Rajan] Any comments?