Re: [PATCH 5/5] arm64: dts: qcom: x1e/x1p: Add EL2 overlay for WoA devices

[Marc Zyngier <maz@kernel.org>]

On Thu, 01 May 2025 18:03:45 +0100,
Nikita Travkin <nikita@trvn.ru> wrote:
> 
> WoA devices using x1e/x1p use android firmware to boot, which notably
> includes Gunyah hypervisor. This means that, so far, Linux-based OS
> could only boot in EL1 on those devices.
> 
> However Windows can replace Gunyah upon boot with it's own hypervisor,
> and with the use of tools such as "slbounce", it's possible to do the
> same for Linux-based OS, in which case some modifications to the DT are
> necessary to facilitate the absence of Gunyah services.
> 
> Add a EL2-specific DT overlay and apply it to x1e/x1p WoA devices to
> create -el2.dtb for each of them alongside "normal" dtb.
> 
> Signed-off-by: Nikita Travkin <nikita@trvn.ru>
> ---
>  arch/arm64/boot/dts/qcom/Makefile      | 36 +++++++++++++++++---------
>  arch/arm64/boot/dts/qcom/x1-el2.dtso   | 46 ++++++++++++++++++++++++++++++++++
>  arch/arm64/boot/dts/qcom/x1e80100.dtsi |  2 +-
>  3 files changed, 71 insertions(+), 13 deletions(-)
>

[...]

> diff --git a/arch/arm64/boot/dts/qcom/x1-el2.dtso b/arch/arm64/boot/dts/qcom/x1-el2.dtso
> new file mode 100644
> index 0000000000000000000000000000000000000000..7a818045ef098b44632df45253d32e31c5c7aeed
> --- /dev/null
> +++ b/arch/arm64/boot/dts/qcom/x1-el2.dtso
> @@ -0,0 +1,46 @@
> +// SPDX-License-Identifier: BSD-3-Clause
> +
> +/*
> + * x1 specific modifications required to boot in EL2.
> + */
> +
> +/dts-v1/;
> +/plugin/;
> +
> +/* We can't and don't need to use zap shader in EL2 as linux can zap the gpu on it's own. */
> +&gpu_zap_shader {
> +	status = "disabled";
> +};
> +
> +/*
> + * When running under Gunyah, this IOMMU is controlled by the firmware,
> + * however when we take ownership of it in EL2, we need to configure
> + * it properly to use PCIe.
> + */
> +&pcie3 {
> +	iommu-map = <0 &pcie_smmu 0x30000 0x10000>;
> +};
> +
> +&pcie4 {
> +	iommu-map = <0 &pcie_smmu 0x40000 0x10000>;
> +};
> +
> +&pcie5 {
> +	iommu-map = <0 &pcie_smmu 0x50000 0x10000>;
> +};
> +
> +&pcie6a {
> +	iommu-map = <0 &pcie_smmu 0x60000 0x10000>;
> +};
> +
> +&pcie_smmu {
> +	status = "okay";
> +};
> +
> +/*
> + * The "SBSA watchdog" is implemented in software in Gunyah
> + * and can't be used when running in EL2.
> + */
> +&sbsa_watchdog {
> +	status = "disabled";
> +};

I also carry this [1] patch to correctly route MSIs from pcie5 to the
ITS. There is no reason not to. The same treatment could be applied to
pcie3, but I never tried it.

Thanks,

	M.

[1] https://lore.kernel.org/linux-arm-kernel/20241024161814.1827514-1-maz@kernel.org/

-- 
Without deviation from the norm, progress is not possible.