Re: [PATCH v2] ARM: tegra: Restore DT ABI on Tegra124 Chromebooks

[Tristan Bastian <tristan-c.bastian@gmx.de>]

Thierry Reding – Mon, 11. February 2019 12:09
> From: Thierry Reding <treding@nvidia.com>
> 
> Commit 482997699ef0 ("ARM: tegra: Fix unit_address_vs_reg DTC warnings
> for /memory") inadventently broke device tree ABI by adding a unit-
> address to the "/memory" node because the device tree compiler flagged
> the missing unit-address as a warning.
> 
> Tegra124 Chromebooks (a.k.a. Nyan) use a bootloader that relies on the
> full name of the memory node in device tree being exactly "/memory". It
> can be argued whether this was a good decision or not, and some other
> bootloaders (such as U-Boot) do accept a unit-address in the name of the
> node, but the device tree is an ABI and we can't break existing setups
> just because the device tree compiler considers it bad practice to omit
> the unit-address nowadays.
> 
> This partially reverts the offending commit and restores device tree ABI
> compatibility.
> 
> Fixes: 482997699ef0 ("ARM: tegra: Fix unit_address_vs_reg DTC warnings for
> /memory")
> Reported-by: Tristan Bastian <tristan-c.bastian@gmx.de>
> Signed-off-by: Thierry Reding <treding@nvidia.com>
> ---
> Changes in v2:
> - remove memory@80000000 node pulled in from tegra124.dtsi
> - add device_type = "memory" property
> 
> arch/arm/boot/dts/tegra124-nyan.dtsi | 17 ++++++++++++++++-
> 1 file changed, 16 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/arm/boot/dts/tegra124-nyan.dtsi
> b/arch/arm/boot/dts/tegra124-nyan.dtsi
> index d5f11d6d987e..bc85b6a166c7 100644
> --- a/arch/arm/boot/dts/tegra124-nyan.dtsi
> +++ b/arch/arm/boot/dts/tegra124-nyan.dtsi
> @@ -13,10 +13,25 @@
> stdout-path = "serial0:115200n8";
> };
> 
> - memory@80000000 {
> + /*
> + * Note that recent version of the device tree compiler (starting with
> + * version 1.4.2) warn about this node containing a reg property, but
> + * missing a unit-address. However, the bootloader on these Chromebook
> + * devices relies on the full name of this node to be exactly /memory.
> + * Adding the unit-address causes the bootloader to create a /memory
> + * node and write the memory bank configuration to that node, which in
> + * turn leads the kernel to believe that the device has 2 GiB of
> + * memory instead of the amount detected by the bootloader.
> + *
> + * The name of this node is effectively ABI and must not be changed.
> + */
> + memory {
> + device_type = "memory";
> reg = <0x0 0x80000000 0x0 0x80000000>;
> };
> 
> + /delete-node/ memory@80000000;
> +
> host1x@50000000 {
> hdmi@54280000 {
> status = "okay";
> -- 
> 2.19.1

Thanks Thierry

Tristan

Tested-by: Tristan Bastian <tristan-c.bastian@gmx.de>

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