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[PATCH 1/2] regmap: Add explict native endian flag to DT bindings

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  [PATCH 1/2] regmap: Add explict native endian flag to DT bindings Mark Brown <broonie@kernel.org> - 2016-01-26 23:50 +0100
    Re: [PATCH 1/2] regmap: Add explict native endian flag to DT bindings Arnd Bergmann <arnd@arndb.de> - 2016-01-27 12:10 +0100
      Re: [PATCH 1/2] regmap: Add explict native endian flag to DT bindings Mark Brown <broonie@kernel.org> - 2016-01-27 13:20 +0100

#1318452 — [PATCH 1/2] regmap: Add explict native endian flag to DT bindings

Currently the binding document says that if no endianness is configured
we use native endian but this is not in fact true for all binding types
and we do have some devices that really want native endianness such as
Broadcom MIPS SoCs where switching the endianness of the CPU also
switches the endianness of external IPs.

Provide an explicit option for this.

Signed-off-by: Mark Brown <broonie@kernel.org>
---
 Documentation/devicetree/bindings/regmap/regmap.txt | 11 +++++++----
 drivers/base/regmap/regmap.c                        |  2 ++
 2 files changed, 9 insertions(+), 4 deletions(-)

diff --git a/Documentation/devicetree/bindings/regmap/regmap.txt b/Documentation/devicetree/bindings/regmap/regmap.txt
index b494f8b8ef72..e98a9652ccc8 100644
--- a/Documentation/devicetree/bindings/regmap/regmap.txt
+++ b/Documentation/devicetree/bindings/regmap/regmap.txt
@@ -5,15 +5,18 @@ Index     Device     Endianness properties
 ---------------------------------------------------
 1         BE         'big-endian'
 2         LE         'little-endian'
+3	  Native     'native-endian'
 
 For one device driver, which will run in different scenarios above
 on different SoCs using the devicetree, we need one way to simplify
 this.
 
-Required properties:
-- {big,little}-endian: these are boolean properties, if absent
-  meaning that the CPU and the Device are in the same endianness mode,
-  these properties are for register values and all the buffers only.
+Optional properties:
+- {big,little,native}-endian: these are boolean properties, if absent
+  then the implementation will choose a default based on the device
+  being controlled.  These properties are for register values and all
+  the buffers only.  Native endian means that the CPU and device have
+  the same endianness.
 
 Examples:
 Scenario 1 : CPU in LE mode & device in LE mode.
diff --git a/drivers/base/regmap/regmap.c b/drivers/base/regmap/regmap.c
index 4ac63c0e50c7..57a7d144e629 100644
--- a/drivers/base/regmap/regmap.c
+++ b/drivers/base/regmap/regmap.c
@@ -500,6 +500,8 @@ enum regmap_endian regmap_get_val_endian(struct device *dev,
 			endian = REGMAP_ENDIAN_BIG;
 		else if (of_property_read_bool(np, "little-endian"))
 			endian = REGMAP_ENDIAN_LITTLE;
+		else if (of_property_read_bool(np, "native-endian"))
+			endian = REGMAP_ENDIAN_NATIVE;
 
 		/* If the endianness was specified in DT, use that */
 		if (endian != REGMAP_ENDIAN_DEFAULT)
-- 
2.7.0.rc3

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#1318859

On Tuesday 26 January 2016 22:46:49 Mark Brown wrote:
> -Required properties:
> -- {big,little}-endian: these are boolean properties, if absent
> -  meaning that the CPU and the Device are in the same endianness mode,
> -  these properties are for register values and all the buffers only.
> +Optional properties:
> +- {big,little,native}-endian: these are boolean properties, if absent
> +  then the implementation will choose a default based on the device
> +  being controlled.  These properties are for register values and all
> +  the buffers only.  Native endian means that the CPU and device have
> +  the same endianness.

I think the rest of the file also needs to be changed, and we need some
more explanation about native-endian, which people might think is the
right one for them when it rarely is in reality (Broadcom MIPS being
one notable exception).

How about this version below?

	Arnd


diff --git a/Documentation/devicetree/bindings/regmap/regmap.txt b/Documentation/devicetree/bindings/regmap/regmap.txt
dissimilarity index 91%
index b494f8b8ef72..0127be360fe8 100644
--- a/Documentation/devicetree/bindings/regmap/regmap.txt
+++ b/Documentation/devicetree/bindings/regmap/regmap.txt
@@ -1,47 +1,29 @@
-Device-Tree binding for regmap
-
-The endianness mode of CPU & Device scenarios:
-Index     Device     Endianness properties
----------------------------------------------------
-1         BE         'big-endian'
-2         LE         'little-endian'
-
-For one device driver, which will run in different scenarios above
-on different SoCs using the devicetree, we need one way to simplify
-this.
-
-Required properties:
-- {big,little}-endian: these are boolean properties, if absent
-  meaning that the CPU and the Device are in the same endianness mode,
-  these properties are for register values and all the buffers only.
-
-Examples:
-Scenario 1 : CPU in LE mode & device in LE mode.
-dev: dev@40031000 {
-	      compatible = "name";
-	      reg = <0x40031000 0x1000>;
-	      ...
-};
-
-Scenario 2 : CPU in LE mode & device in BE mode.
-dev: dev@40031000 {
-	      compatible = "name";
-	      reg = <0x40031000 0x1000>;
-	      ...
-	      big-endian;
-};
-
-Scenario 3 : CPU in BE mode & device in BE mode.
-dev: dev@40031000 {
-	      compatible = "name";
-	      reg = <0x40031000 0x1000>;
-	      ...
-};
-
-Scenario 4 : CPU in BE mode & device in LE mode.
-dev: dev@40031000 {
-	      compatible = "name";
-	      reg = <0x40031000 0x1000>;
-	      ...
-	      little-endian;
-};
+Devicetree binding for regmap
+
+Optional properties:
+
+   little-endian,
+   big-endian,
+   native-endian:	See common-properties.txt for a definition
+
+Note:
+Regmap defaults to little-endian register access on MMIO based
+devices, this is by far the most common setting. On CPU
+architectures that typically run big-endian operating systems
+(e.g. PowerPC), registers can be defined as big-endian and must
+be marked that way in the devicetree.
+
+On SoCs that can be operated in both big-endian and little-endian
+modes, with a single hardware switch controlling both the endianess
+of the CPU and a byteswap for MMIO registers (e.g. many Broadcom MIPS
+chips), "native-endian" is used to allow using the same device tree
+blob in both cases.
+
+Examples:
+Scenario 1 : a register set in big-endian mode.
+dev: dev@40031000 {
+	      compatible = "syscon";
+	      reg = <0x40031000 0x1000>;
+	      big-endian;
+	      ...
+};

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#1318912

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On Wed, Jan 27, 2016 at 12:02:19PM +0100, Arnd Bergmann wrote:

> I think the rest of the file also needs to be changed, and we need some
> more explanation about native-endian, which people might think is the
> right one for them when it rarely is in reality (Broadcom MIPS being
> one notable exception).

I'm not sure it's *that* confusing at this point but this is definitely
a lot clearer.

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