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ARM: 8335/1: Documentation: DT bindings: Tegra AHB: document the legacy base address

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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
Acked-by: Stephen Warren <swarren@nvidia.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
This commit is contained in:
Paul Walmsley 2015-03-26 08:58:31 +01:00 committed by Russell King
parent ce7a10b0ff
commit 38e42f1216
1 changed files with 5 additions and 2 deletions
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7
Documentation/devicetree/bindings/arm/tegra/nvidia,tegra20-ahb.txt
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@ -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>.
Example:
Example (for a Tegra20 chip):
ahb: ahb@6000c004 {
compatible = "nvidia,tegra20-ahb";
reg = <0x6000c004 0x10c>; /* AHB Arbitration + Gizmo Controller */