[v3,3/3] Documentation: DT bindings: Tegra AHB: require the legacy base address for existing chips

Per Stephen Warren, note in the Tegra AHB DT binding documentation
that we specifically deprecate any attempt to use the IP block's
actual hardware base address, and advocate the use of the legacy
"off-by-four" address in the 'regs' property, for Tegra chips with
existing upstream Linux DT files that include a Tegra AHB node.  This
patch updates the documentation accordingly.

Changing the existing kernel DT data isn't under consideration because
Linux kernel DT data policy is to preserve compatibility between newer
DT data files and older kernels.  However, this additional step of
changing the documentation should discourage others from sending
kernel patches to try to change the legacy kernel DT data.
Furthermore, for out-of-tree software (such as bootloaders or other
operating systems) that may rely on Linux kernel DT binding
documentation as an ABI (but not the Linux kernel DT data itself),
such a change may allow future convergence with the Linux kernel DT
data without additional code changes.

Signed-off-by: Paul Walmsley <paul@pwsan.com>
Cc: Paul Walmsley <pwalmsley@nvidia.com>
Cc: Stephen Warren <swarren@wwwdotorg.org>
Cc: Alexandre Courbot <gnurou@gmail.com>
Cc: Eduardo Valentin <edubezval@gmail.com>
Cc: Ian Campbell <ijc+devicetree@hellion.org.uk>
Cc: Kumar Gala <galak@codeaurora.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Pawel Moll <pawel.moll@arm.com>
Cc: Rob Herring <robh+dt@kernel.org>
Cc: Thierry Reding <thierry.reding@gmail.com>
Cc: devicetree@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
---
 .../bindings/arm/tegra/nvidia,tegra20-ahb.txt      |    7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)



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On 03/20/2015 12:11 AM, Paul Walmsley wrote:
> Per Stephen Warren, note in the Tegra AHB DT binding documentation
> that we specifically deprecate any attempt to use the IP block's
> actual hardware base address, and advocate the use of the legacy
> "off-by-four" address in the 'regs' property, for Tegra chips with
> existing upstream Linux DT files that include a Tegra AHB node.  This
> patch updates the documentation accordingly.
>
> Changing the existing kernel DT data isn't under consideration because
> Linux kernel DT data policy is to preserve compatibility between newer
> DT data files and older kernels.  However, this additional step of
> changing the documentation should discourage others from sending
> kernel patches to try to change the legacy kernel DT data.
> Furthermore, for out-of-tree software (such as bootloaders or other
> operating systems) that may rely on Linux kernel DT binding
> documentation as an ABI (but not the Linux kernel DT data itself),
> such a change may allow future convergence with the Linux kernel DT
> data without additional code changes.

> diff --git a/Documentation/devicetree/bindings/arm/tegra/nvidia,tegra20-ahb.txt b/Documentation/devicetree/bindings/arm/tegra/nvidia,tegra20-ahb.txt
> index 067c9790062f..9a4295b54539 100644
> --- a/Documentation/devicetree/bindings/arm/tegra/nvidia,tegra20-ahb.txt
> +++ b/Documentation/devicetree/bindings/arm/tegra/nvidia,tegra20-ahb.txt
> @@ -5,9 +5,12 @@ Required properties:
>     Tegra30, must contain "nvidia,tegra30-ahb".  Otherwise, must contain
>     '"nvidia,<chip>-ahb", "nvidia,tegra30-ahb"' where <chip> is tegra124,
>     tegra132, or tegra210.
> -- reg : Should contain 1 register ranges(address and length)
> +- reg : Should contain 1 register ranges(address and length).  For
> +  Tegra20, Tegra30, and Tegra114 chips, the value must be <0x6000c004
> +  0x10c>.  For Tegra124, Tegra132 and Tegra210 chips, the value should
> +  be be <0x6000c000 0x150>.

I would have expected the exception to exist on Tegra124 too since 
that's long been supported upstream. However, since we haven't actually 
added the AHB node into the DT files on Tegra124 yet, I suppose we can 
assume that nobody has anywhere so the slightly retro-active change on 
Tegra124 is OK.

The series,
Acked-by: Stephen Warren <swarren@nvidia.com>

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