Re: [PATCH 01/31] ARM: tegra: add missing clock documentation to DT bindings

[Thierry Reding <thierry.reding-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>]

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On Wed, Dec 04, 2013 at 10:34:17AM -0700, Stephen Warren wrote:
> On 12/04/2013 01:48 AM, Thierry Reding wrote:
> > On Tue, Dec 03, 2013 at 11:31:00AM -0700, Stephen Warren wrote:
> >> On 12/02/2013 01:52 AM, Thierry Reding wrote:
> >>> On Sun, Dec 01, 2013 at 12:05:44PM -0700, Stephen Warren 
> >>> wrote:
> >>>> On 11/29/2013 04:49 AM, Thierry Reding wrote:
> >>>>> On Fri, Nov 15, 2013 at 01:53:56PM -0700, Stephen Warren 
> >>>>> wrote: [...]
> >>>>>> @@ -60,6 +81,12 @@ of the following host1x client 
> >>>>>> modules: - compatible: "nvidia,tegra<chip>-dc" - reg: 
> >>>>>> Physical base address and length of the controller's 
> >>>>>> registers. - interrupts: The interrupt outputs from the 
> >>>>>> controller. +  - clocks : Must contain an entry for each 
> >>>>>> entry in clock-names. +    See 
> >>>>>> ../clocks/clock-bindings.txt for details. +  - 
> >>>>>> clock-names : Must include the following entries: +    -
> >>>>>>  disp1 or disp2 (depending on the controller instance)
> >>>>> 
> >>>>> I'm not sure if this makes sense. The name could be the 
> >>>>> same independent of which controller uses it. If it isn't 
> >>>>> then the driver would need additional code to find out 
> >>>>> which instance it is and construct a dynamic string.
> >>>>> 
> >>>>> Any objection to just make this entry "disp", or "dc"?
> >>>> 
> >>>> This patch simply documents the binding that the various 
> >>>> drivers already require and/or whatever is already in the DT 
> >>>> files if there are any clocks the drivers don't currently 
> >>>> use. I did consider fixing up all the current usage to 
> >>>> actually be sane, but that would require even more driver 
> >>>> changes (in addition to those required for the reset 
> >>>> framework patches).
> >>> 
> >>> Okay, I understand. I still think we should change the usage 
> >>> for this particular use-case subsequently. In retrospect the 
> >>> entry in clock-names wasn't thought out very well. It seems 
> >>> like the reason for using disp1 and disp2 respectively was so 
> >>> that it would match the system-wide clock name, rather than
> >>> the clock's label within the display controller's context.
> >>> 
> >>> Just to clarify what I mean, if we stick to the above, then 
> >>> we'll need to add code to the driver along the lines of:
> >>> 
> >>> char clock_name[6];
> >>> 
> >>> if (regs->start == 0x54200000) index = 1; else index = 2;
> >>> 
> >>> sprintf(clock_name, "disp%u", index);
> >>> 
> >>> clk = devm_clk_get(&pdev->dev, clock_name);
> >>> 
> >>> rather than the much more simple and elegant:
> >>> 
> >>> clk = devm_clk_get(&pdev->dev, "disp");
> >>> 
> >>> The whole purpose of the clock consumer ID is to be generic
> >>> and as such independent of the specific IP block or instance 
> >>> thereof.
> >> 
> >> I think if the code needs this clock, I'd be tempted to do the 
> >> following:
> >> 
> >> clk = clk_get(dev, "disp1"); if (IS_ERR(clk) && PTR_ERR(clk) != 
> >> -EPROBE_DEFERRED) clk = clk_get(dev, "disp2"); if (IS_ERR(clk)) 
> >> return PTR_ERR(clk);
> >> 
> >> That avoids having to hard-code IP block base addresses and 
> >> construct clock names at run-time.
> > 
> > I think perhaps we're getting our wires crossed. What I've been 
> > trying to say is that I think the binding should define the first 
> > clock to be named simply "disp".
> > 
> > The reason why I think "disp" is a better choice than "disp1" and 
> > "disp2" is that it merely encodes the purpose of the clock for the
> >  display controller, and doesn't contain knowledge about the 
> > particular instance of the display controller. That's analogous to 
> > I2C or SPI nodes where the clock isn't named "i2c1", "i2c2", ...
> > or "spi1", "spi2", ... but simply "i2c" or "spi" respectively.
> > 
> > I know that existing DTS files use "disp1" and "disp2", 
> > respectively, but I think that was a wrong choice back at the time 
> > and therefore I suggest that we change it while we still can (DTS 
> > files are changing in 3.14 anyway because of the reset and DMA 
> > binding updates).
> > 
> > Is that any clearer than what I was saying before?
> 
> No, because I know what you meant before:-)
> 
> The thing I was missing is that the existing disp1/disp2 naming is
> /only/ something that's in the DT. The driver (and hence the exiting
> as-yet-undocumented ABI) looks up this clock as "index 0" not as "name
> disp1". Hence, we /can/ change the documented name without affecting
> the ABI at all, and not affecting the ABI is something I was trying to
> avoid in this patch.

Excellent. Glad we're finally on the same page.

> So, how about I fold the following into this patch:
> 
> > diff --git a/Documentation/devicetree/bindings/gpu/nvidia,tegra20-host1x.txt b/Documentation/devicetree/bindings/gpu/nvidia,tegra20-host1x.txt
> > index 42fe3a498e71..ab45c02aa658 100644
> > --- a/Documentation/devicetree/bindings/gpu/nvidia,tegra20-host1x.txt
> > +++ b/Documentation/devicetree/bindings/gpu/nvidia,tegra20-host1x.txt
> > @@ -111,7 +111,7 @@ of the following host1x client modules:
> >    - clocks: Must contain an entry for each entry in clock-names.
> >      See ../clocks/clock-bindings.txt for details.
> >    - clock-names: Must include the following entries:
> > -    - disp1 or disp2 (depending on the controller instance)
> > +    - dc
> >        This MUST be the first entry.
> >      - parent
> >    - resets: Must contain an entry for each entry in reset-names.
> > diff --git a/arch/arm/boot/dts/tegra20.dtsi b/arch/arm/boot/dts/tegra20.dtsi
> > index 01c20c7dbb51..648c494e927f 100644
> > --- a/arch/arm/boot/dts/tegra20.dtsi
> > +++ b/arch/arm/boot/dts/tegra20.dtsi
> > @@ -89,7 +89,7 @@
> >                         interrupts = <GIC_SPI 73 IRQ_TYPE_LEVEL_HIGH>;
> >                         clocks = <&tegra_car TEGRA20_CLK_DISP1>,
> >                                  <&tegra_car TEGRA20_CLK_PLL_P>;
> > -                       clock-names = "disp1", "parent";
> > +                       clock-names = "dc", "parent";
> >                         resets = <&tegra_car 27>;
> >                         reset-names = "dc";
> >  
> > @@ -104,7 +104,7 @@
> >                         interrupts = <GIC_SPI 74 IRQ_TYPE_LEVEL_HIGH>;
> >                         clocks = <&tegra_car TEGRA20_CLK_DISP2>,
> >                                  <&tegra_car TEGRA20_CLK_PLL_P>;
> > -                       clock-names = "disp2", "parent";
> > +                       clock-names = "dc", "parent";
> >                         resets = <&tegra_car 26>;
> >                         reset-names = "dc";
> >  
> > diff --git a/arch/arm/boot/dts/tegra30.dtsi b/arch/arm/boot/dts/tegra30.dtsi
> > index 58a3dca24c49..829eb4b5091d 100644
> > --- a/arch/arm/boot/dts/tegra30.dtsi
> > +++ b/arch/arm/boot/dts/tegra30.dtsi
> > @@ -165,7 +165,7 @@
> >                         interrupts = <GIC_SPI 73 IRQ_TYPE_LEVEL_HIGH>;
> >                         clocks = <&tegra_car TEGRA30_CLK_DISP1>,
> >                                  <&tegra_car TEGRA30_CLK_PLL_P>;
> > -                       clock-names = "disp1", "parent";
> > +                       clock-names = "dc", "parent";
> >                         resets = <&tegra_car 27>;
> >                         reset-names = "dc";
> >  
> > @@ -180,7 +180,7 @@
> >                         interrupts = <GIC_SPI 74 IRQ_TYPE_LEVEL_HIGH>;
> >                         clocks = <&tegra_car TEGRA30_CLK_DISP2>,
> >                                  <&tegra_car TEGRA30_CLK_PLL_P>;
> > -                       clock-names = "disp2", "parent";
> > +                       clock-names = "dc", "parent";
> >                         resets = <&tegra_car 26>;
> >                         reset-names = "dc";
> >  

That looks perfect. Thanks!

Thierry

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