linux-kernel - Re: [PATCH] dt-bindings: timer: Use non-empty ranges in example

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Date:   Mon, 16 Dec 2019 22:16:56 -0800
From:   Doug Anderson <dianders@...omium.org>
To:     Rob Herring <robh+dt@...nel.org>
Cc:     Bjorn Andersson <bjorn.andersson@...aro.org>,
        Matthias Kaehlcke <mka@...omium.org>,
        Andy Gross <agross@...nel.org>,
        Rajendra Nayak <rnayak@...eaurora.org>,
        Stephen Boyd <swboyd@...omium.org>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>, LKML <linux-kernel@...r.kernel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Mark Rutland <mark.rutland@....com>,
        Daniel Lezcano <daniel.lezcano@...aro.org>
Subject: Re: [PATCH] dt-bindings: timer: Use non-empty ranges in example

Hi,

On Mon, Dec 16, 2019 at 10:06 PM Douglas Anderson <dianders@...omium.org> wrote:
>
> On many arm64 qcom device trees, running `make dtbs_check` yells:
>
>   timer@...20000: #size-cells:0:0: 1 was expected
>
> It appears that someone was trying to assert the fact that sub-nodes
> describing frames would never have a size that's more than 32-bits
> big.  That does indeed appear to be true for all cases I could find.
>
> Currently many arm64 qcom device tree files have a #address-cells and
> about in commit bede7d2dc8f3 ("arm64: dts: qcom: sdm845: Increase
> address and size cells for soc").  That means the only way we can
> shrink them down is to use a non-empty ranges.
>
> Since forever it has said in "writing-bindings.txt" to "DO use
> non-empty 'ranges' to limit the size of child buses/devices".  I guess
> we should start listening to it.
>
> I believe (but am not certain) that this also means that we should use
> "ranges" to simplify the "reg" of our sub devices by specifying an
> offset.  Let's update the example in the bindings to make this
> obvious.
>
> Signed-off-by: Douglas Anderson <dianders@...omium.org>
> ---
> See:
>   https://lore.kernel.org/r/20191212113540.7.Ia9bd3fca24ad34a5faaf1c3e58095c74b38abca1@changeid
>
> ...for the patch that sparked this change.
>
>  .../devicetree/bindings/timer/arm,arch_timer_mmio.yaml | 10 +++++-----
>  1 file changed, 5 insertions(+), 5 deletions(-)
>
> diff --git a/Documentation/devicetree/bindings/timer/arm,arch_timer_mmio.yaml b/Documentation/devicetree/bindings/timer/arm,arch_timer_mmio.yaml
> index b3f0fe96ff0d..d927b42ddeb8 100644
> --- a/Documentation/devicetree/bindings/timer/arm,arch_timer_mmio.yaml
> +++ b/Documentation/devicetree/bindings/timer/arm,arch_timer_mmio.yaml
> @@ -99,22 +99,22 @@ examples:
>        compatible = "arm,armv7-timer-mem";
>        #address-cells = <1>;
>        #size-cells = <1>;
> -      ranges;
> +      ranges = <0 0xf0000000 0x1000>;

I checked this over a few times and yet I still screwed it up.  :(
This should be:

ranges = <0 0xf0001000 0x1000>;

...which makes the first "frame" below actually start at 0.  I'll wait
before sending out a v2, though, in case this patch is totally wrong
or something.


>        reg = <0xf0000000 0x1000>;
>        clock-frequency = <50000000>;
>
> -      frame@...01000 {
> +      frame@0 {
>          frame-number = <0>;
>          interrupts = <0 13 0x8>,
>                 <0 14 0x8>;
> -        reg = <0xf0001000 0x1000>,
> -              <0xf0002000 0x1000>;
> +        reg = <0x0000 0x1000>,
> +              <0x1000 0x1000>;
>        };
>
>        frame@...03000 {
>          frame-number = <1>;
>          interrupts = <0 15 0x8>;
> -        reg = <0xf0003000 0x1000>;
> +        reg = <0x2000 0x1000>;
>        };
>      };