Re: [PATCH RFC 2/2] MIPS: dt: Explicitly specify native endian behaviour for syscon

[Florian Fainelli]

On 26/01/16 14:46, Mark Brown wrote:
> On many MIPS systems the endianness of IP blocks is kept the same as
> that of the CPU by the hardware.  This includes the system controllers
> on these systems which are controlled via syscon which uses the regmap
> API which used readl() and writel() to interact with the hardware,
> meaning that all writes are converted to little endian when writing to
> the hardware.  This caused a bad interaction with the regmap core in big
> endian mode since it was not aware of the byte swapping and so ended up
> performing little endian writes.
> 
> Unfortunately when this issue was noticed it was addressed by updating
> the DT for the affected devices to specify them as little endian.  This
> happened to work since it resulted in two endianness swaps which
> cancelled each other out and gave little endian behaviour but meant that
> the DT was clearly not accurately describing the hardware.
> 
> The intention of commit 29bb45f25ff305 (regmap-mmio: Use native
> endianness for read/write) was to fix this by making regmap default to
> native endianness but this breaks most other MMIO users where the
> hardware has a fixed endianness and the implementation uses the __raw
> accessors which are not intended to be used outside of architecture
> code.  Instead use the newly added native-endian DT property to say
> exactly what we want for these systems.
> 
> Fixes: 29bb45f25ff305 (regmap-mmio: Use native endianness for read/write)
> Reported-by: Johannes Berg <johannes@xxxxxxxxxxxxxxxx>
> Signed-off-by: Mark Brown <broonie@xxxxxxxxxx>
> ---
> 
> Posted for review only, this will interact with some other patches
> fixing the implementation of regmap-mmio and will probably need to be
> merged along with them.
> 
>  arch/mips/boot/dts/brcm/bcm6328.dtsi | 1 +

v4.5-rc1 now contains an arch/mips/boot/dts/brcm/bcm6368.dtsi which
copied the 6328.dtsi and therefore needs this hunk to be added to your
patch series:

diff --git a/arch/mips/boot/dts/brcm/bcm6368.dtsi
b/arch/mips/boot/dts/brcm/bcm6368.dtsi
index 9c8d3fe28b31..1f6b9b5cddb4 100644
--- a/arch/mips/boot/dts/brcm/bcm6368.dtsi
+++ b/arch/mips/boot/dts/brcm/bcm6368.dtsi
@@ -54,7 +54,7 @@
                periph_cntl: syscon@10000000 {
                        compatible = "syscon";
                        reg = <0x10000000 0x14>;
-                       little-endian;
+                       native-endian;
                };

                reboot: syscon-reboot@10000008 {
-- 
Florian