[U-Boot] [PATCH 6/8] ARMv8: PSCI: Fixup the device tree for PSCI v0.2

Mark Rutland
2014-08-28T12:44:48Z

Hi,

On Wed, Aug 27, 2014 at 09:29:59PM +0100, Arnab Basu wrote:
> Set the enable-method in the cpu node to psci, create the psci
> device tree node and also add a reserve section for the psci code
> that lives in in normal RAM, so that the kernel leaves it alone
>
> Signed-off-by: Arnab Basu <arnab.basu@freescale.com>
> Reviewed-by: Bhupesh Sharma <bhupesh.sharma@freescale.com>
> Cc: Marc Zyngier <marc.zyngier@arm.com>
> ---
> arch/arm/cpu/armv8/cpu-dt.c | 67 +++++++++++++++++++++++++++++++++++++++++
> arch/arm/include/asm/system.h | 4 ++
> 2 files changed, 71 insertions(+), 0 deletions(-)
>
> diff --git a/arch/arm/cpu/armv8/cpu-dt.c b/arch/arm/cpu/armv8/cpu-dt.c
> index 9792bc0..c2c8fe7 100644
> --- a/arch/arm/cpu/armv8/cpu-dt.c
> +++ b/arch/arm/cpu/armv8/cpu-dt.c
> @@ -9,7 +9,69 @@
> #include <fdt_support.h>
>
> #ifdef CONFIG_MP
> +#ifdef CONFIG_ARMV8_PSCI
>
> +static void psci_reserve_mem(void *fdt)
> +{
> +#ifndef CONFIG_ARMV8_SECURE_BASE
> + /* secure code lives in RAM, keep it alive */
> + fdt_add_mem_rsv(fdt, (unsigned long)__secure_start,
> + __secure_end - __secure_start);
> +#endif
> +}

With PSCI I'd be worried about telling the OS about this memory at all.

If the OS maps the memory we could encounter issues with mismatched
aliases and/or unexpected hits in the D-cache, which can result in a
loss of ordering and/or visbility guarantees, which could break the PSCI
implementation.

With the KVM or trusted firmware PSCI implementations the (guest) OS
cannot map the implementation's memory, preventing such problems. The
arm64 Linux boot-wrapper is dodgy in this regard currently.

> +static int cpu_update_dt_psci(void *fdt)
> +{
> + int nodeoff;
> + int tmp;
> +
> + psci_reserve_mem(fdt);
> +
> + nodeoff = fdt_path_offset(fdt, "/cpus");
> + if (nodeoff < 0) {
> + printf("couldn't find /cpus\n");
> + return nodeoff;
> + }
> +
> + /* add 'enable-method = "psci"' to each cpu node */
> + for (tmp = fdt_first_subnode(fdt, nodeoff);
> + tmp >= 0;
> + tmp = fdt_next_subnode(fdt, tmp)) {
> + const struct fdt_property *prop;
> + int len;
> +
> + prop = fdt_get_property(fdt, tmp, "device_type", &len);
> + if (!prop)
> + continue;
> + if (len < 4)
> + continue;
> + if (strcmp(prop->data, "cpu"))
> + continue;
> +
> + fdt_setprop_string(fdt, tmp, "enable-method", "psci");

Do we need to check the return code here, as we do when setting up the
psci node?

> + }
> +
> + nodeoff = fdt_path_offset(fdt, "/psci");

We might need to search by compatible string. All psci nodes so far have
been called /psci, but that's not guaranteed. Linux looks for nodes
compatible with "arm,psci" and/or "arm,psci-0.2".

> + if (nodeoff < 0) {
> + nodeoff = fdt_path_offset(fdt, "/");
> + if (nodeoff < 0)
> + return nodeoff;
> +
> + nodeoff = fdt_add_subnode(fdt, nodeoff, "psci");
> + if (nodeoff < 0)
> + return nodeoff;
> + }
> +
> + tmp = fdt_setprop_string(fdt, nodeoff, "compatible", "arm,psci-0.2");
> + if (tmp)
> + return tmp;
> + tmp = fdt_setprop_string(fdt, nodeoff, "method", "smc");
> + if (tmp)
> + return tmp;
> +
> + return 0;
> +}

Otherwise this looks fine.

Mark.