[PATCH] mach-snapdragon: handle platforms without PSCI support

[Mark Kettenis]

> Date: Mon, 27 Jan 2025 14:48:55 +0000
> From: Sam Day <me at samcday.com>

Hi Sam,

> Most MSM8916 devices shipped without PSCI support. The history is quite
> nuanced (a good overview can be found in [1]), but the end result is
> that the upstream DTs for this SoC pretend that PSCI exists, and it's
> expected that the bootloader handles the case where it doesn't. This is
> codified by the de-facto bootloader for MSM8916 devices, lk2nd [2].
> 
> So we handle it here by deleting the /psci node if we detect the absence
> of PSCI. We need to do this early to ensure sysreset works correctly,
> since the PSCI firmware driver is PRE_RELOC and binds the PSCI sysreset
> driver.

But deleting the /psci node isn't enough is it?  At least on systems
with more than a single core the OS will need a way to spin up the
additonal cores.  So you'll need to modify the CPU nodes as well and
change the "enable-method" property to "spin-table" and add the
necessary infrastructure for that.

> Additionally, show_psci_version is updated to check that PSCI exists.
> Currently this banner outputs "PSCI: 65535.65535" on devices without
> PSCI support, which isn't very useful :)
> 
> [1]: https://github.com/msm8916-mainline/linux/issues/388
> [2]: https://github.com/msm8916-mainline/lk2nd/blob/8183ea2/lk2nd/smp/spin-table/spin-table.c#L237
> 
> Signed-off-by: Sam Day <me at samcday.com>
> ---
>  arch/arm/mach-snapdragon/board.c | 43 ++++++++++++++++++++++++++++++++++++----
>  1 file changed, 39 insertions(+), 4 deletions(-)
> 
> diff --git a/arch/arm/mach-snapdragon/board.c b/arch/arm/mach-snapdragon/board.c
> index e87551784b8d7afb4186533d43b8bddacba9faec..75b9cf1a8a1b3383665eb2d4e6725efe59718de0 100644
> --- a/arch/arm/mach-snapdragon/board.c
> +++ b/arch/arm/mach-snapdragon/board.c
> @@ -162,11 +162,42 @@ static void show_psci_version(void)
>  
>  	arm_smccc_smc(ARM_PSCI_0_2_FN_PSCI_VERSION, 0, 0, 0, 0, 0, 0, 0, &res);
>  
> +	/* Some older SoCs like MSM8916 don't always support PSCI */
> +	if ((int)res.a0 == PSCI_RET_NOT_SUPPORTED)
> +		return;
> +
>  	debug("PSCI:  v%ld.%ld\n",
>  	      PSCI_VERSION_MAJOR(res.a0),
>  	      PSCI_VERSION_MINOR(res.a0));
>  }
>  
> +/**
> + * Most MSM8916 devices in the wild shipped without PSCI support, but the
> + * upstream DTs pretend that PSCI exists. If that situation is detected here,
> + * the /psci node is deleted. This is done very early to ensure the PSCI
> + * firmware driver doesn't bind (which then binds a sysreset driver that won't
> + * work).
> + */
> +static void qcom_psci_fixup(void *fdt)
> +{
> +	int offset, ret;
> +	struct arm_smccc_res res;
> +
> +	arm_smccc_smc(ARM_PSCI_0_2_FN_PSCI_VERSION, 0, 0, 0, 0, 0, 0, 0, &res);
> +
> +	if ((int)res.a0 != PSCI_RET_NOT_SUPPORTED)
> +		return;
> +
> +	offset = fdt_path_offset(fdt, "/psci");
> +	if (offset < 0)
> +		return;
> +
> +	debug("Found /psci DT node on device with no PSCI. Deleting.\n");
> +	ret = fdt_del_node(fdt, offset);
> +	if (ret)
> +		log_err("Failed to delete /psci node: %d\n", ret);
> +}
> +
>  /* We support booting U-Boot with an internal DT when running as a first-stage bootloader
>   * or for supporting quirky devices where it's easier to leave the downstream DT in place
>   * to improve ABL compatibility. Otherwise, we use the DT provided by ABL.
> @@ -212,12 +243,16 @@ int board_fdt_blob_setup(void **fdtp)
>  
>  	if (internal_valid) {
>  		debug("Using built in FDT\n");
> -		return -EEXIST;
> +		ret = -EEXIST;
> +	} else {
> +		debug("Using external FDT\n");
> +		*fdtp = external_fdt;
> +		ret = 0;
>  	}
>  
> -	debug("Using external FDT\n");
> -	*fdtp = external_fdt;
> -	return 0;
> +	qcom_psci_fixup(*fdtp);
> +
> +	return ret;
>  }
>  
>  void reset_cpu(void)
> 
> ---
> base-commit: 2eed5a1ff36217372e19f7513bd07077fc76718a
> change-id: 20250127-qcom-handle-absent-psci-6e8e8af7bcd7
> prerequisite-change-id: 20250120-qcom-parse-memory-updates-96ffe248cdf1:v3
> prerequisite-patch-id: 65448b5a93120d2117c1361035afc9bd911d005f
> 
> Best regards,
> -- 
> Sam Day <me at samcday.com>
> 
> 
>