Re: [PATCH v5 04/19] firmware/psci: Add psci_early_test_conduit()

[Gavin Shan <gshan@redhat.com>]

On 8/19/24 11:19 PM, Steven Price wrote:
> From: Jean-Philippe Brucker <jean-philippe@linaro.org>
> 
> Add a function to test early if PSCI is present and what conduit it
> uses. Because the PSCI conduit corresponds to the SMCCC one, this will
> let the kernel know whether it can use SMC instructions to discuss with
> the Realm Management Monitor (RMM), early enough to enable RAM and
> serial access when running in a Realm.
> 
> Signed-off-by: Jean-Philippe Brucker <jean-philippe@linaro.org>
> Signed-off-by: Steven Price <steven.price@arm.com>
> ---
> v4: New patch
> ---
>   drivers/firmware/psci/psci.c | 25 +++++++++++++++++++++++++
>   include/linux/psci.h         |  5 +++++
>   2 files changed, 30 insertions(+)
> 

Question: Do we need same check for ACPI based system?

> diff --git a/drivers/firmware/psci/psci.c b/drivers/firmware/psci/psci.c
> index 2328ca58bba6..2b308f97ef2c 100644
> --- a/drivers/firmware/psci/psci.c
> +++ b/drivers/firmware/psci/psci.c
> @@ -13,6 +13,7 @@
>   #include <linux/errno.h>
>   #include <linux/linkage.h>
>   #include <linux/of.h>
> +#include <linux/of_fdt.h>
>   #include <linux/pm.h>
>   #include <linux/printk.h>
>   #include <linux/psci.h>
> @@ -769,6 +770,30 @@ int __init psci_dt_init(void)
>   	return ret;
>   }
>   
> +/*
> + * Test early if PSCI is supported, and if its conduit matches @conduit
> + */

Nit: The comments needn't span into multiple lines.

> +bool __init psci_early_test_conduit(enum arm_smccc_conduit conduit)
> +{
> +	int len;
> +	int psci_node;
> +	const char *method;
> +	unsigned long dt_root;
> +
> +	/* DT hasn't been unflattened yet, we have to work with the flat blob */
> +	dt_root = of_get_flat_dt_root();
> +	psci_node = of_get_flat_dt_subnode_by_name(dt_root, "psci");
> +	if (psci_node <= 0)
> +		return false;
> +

Nit: Strictly speaking, "psci_node == 0" isn't an error. So the check would be
"if (psci_node < 0)" if I'm correct.

> +	method = of_get_flat_dt_prop(psci_node, "method", &len);
> +	if (!method)
> +		return false;
> +
> +	return  (conduit == SMCCC_CONDUIT_SMC && strncmp(method, "smc", len) == 0) ||
> +		(conduit == SMCCC_CONDUIT_HVC && strncmp(method, "hvc", len) == 0);
> +}
> +
>   #ifdef CONFIG_ACPI
>   /*
>    * We use PSCI 0.2+ when ACPI is deployed on ARM64 and it's
> diff --git a/include/linux/psci.h b/include/linux/psci.h
> index 4ca0060a3fc4..a1fc1703ba20 100644
> --- a/include/linux/psci.h
> +++ b/include/linux/psci.h
> @@ -45,8 +45,13 @@ struct psci_0_1_function_ids get_psci_0_1_function_ids(void);
>   
>   #if defined(CONFIG_ARM_PSCI_FW)
>   int __init psci_dt_init(void);
> +bool __init psci_early_test_conduit(enum arm_smccc_conduit conduit);
>   #else
>   static inline int psci_dt_init(void) { return 0; }
> +static inline bool psci_early_test_conduit(enum arm_smccc_conduit conduit)
> +{
> +	return false;
> +}
>   #endif
>   
>   #if defined(CONFIG_ARM_PSCI_FW) && defined(CONFIG_ACPI)

Thanks,
Gavin