[PATCH v3 1/3] firmware: psci: Fix bind_smccc_features psci check

[Igor Opaniuk]

Hello Weizhao,

On Wed, Jan 31, 2024 at 3:15 PM Weizhao Ouyang <o451686892 at gmail.com> wrote:
>
> According to PSCI specification DEN0022F, PSCI_FEATURES is used to check
> whether the SMCCC is implemented by discovering SMCCC_VERSION.
>
Could you please add more details to your commit message or as a comment
explaining what exact steps should be done for a full discovery sequence of Arm
Architecture Service functions, so people don't need to search for
that information explicitly?

For instance:
Step 1: Determine if SMCCC_VERSION is implemented
- Use firmware data, device tree PSCI node, or ACPI FADT PSCI flag, to
determine whether a
PSCI implementation is present.
- Use PSCI_VERSION to learn whether PSCI_FEATURES is provided. PSCI_FEATURES is
mandatory from version 1.0 of PSCI
Step 2. etc.

I would just pull that info from the latest SMC Calling Convention version 1.5,
from 9 Appendix B: Discovery of Arm Architecture Service functions.

Thank you!
> Signed-off-by: Weizhao Ouyang <o451686892 at gmail.com>
> ---
> v3: remove fallback smc call
> v2: check SMCCC_ARCH_FEATURES
> ---
>  drivers/firmware/psci.c   | 5 ++++-
>  include/linux/arm-smccc.h | 6 ++++++
>  2 files changed, 10 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/firmware/psci.c b/drivers/firmware/psci.c
> index c6b9efab41..03544d76ed 100644
> --- a/drivers/firmware/psci.c
> +++ b/drivers/firmware/psci.c
> @@ -135,10 +135,13 @@ static int bind_smccc_features(struct udevice *dev, int psci_method)
>             PSCI_VERSION_MAJOR(psci_0_2_get_version()) == 0)
>                 return 0;
>
> -       if (request_psci_features(ARM_SMCCC_ARCH_FEATURES) ==
> +       if (request_psci_features(ARM_SMCCC_VERSION) ==
>             PSCI_RET_NOT_SUPPORTED)
>                 return 0;
>
> +       if (invoke_psci_fn(ARM_SMCCC_VERSION, 0, 0, 0) < ARM_SMCCC_VERSION_1_1)
> +               return 0;
> +
IMO, to fully comply with SMC Calling Convention version 1.5
we should also check for SMCCC_ARCH_WORKAROUND_1:

>From 9 Appendix B: Discovery of Arm Architecture Service functions,
Step 2: Determine if Arm Architecture Service function is implemented
- Use SMCCC_VERSION to learn whether the calling convention complies
to version 1.1 or above.
- Use SMCCC_ARCH_FEATURES to query whether the Arm Architecture
Service function is implemented
on this system <--- we lack of this step

>         if (psci_method == PSCI_METHOD_HVC)
>                 pdata->invoke_fn = smccc_invoke_hvc;
>         else
> diff --git a/include/linux/arm-smccc.h b/include/linux/arm-smccc.h
> index f44e9e8f93..da3d29aabe 100644
> --- a/include/linux/arm-smccc.h
> +++ b/include/linux/arm-smccc.h
> @@ -55,8 +55,14 @@
>  #define ARM_SMCCC_QUIRK_NONE           0
>  #define ARM_SMCCC_QUIRK_QCOM_A6                1 /* Save/restore register a6 */
>
> +#define ARM_SMCCC_VERSION              0x80000000
>  #define ARM_SMCCC_ARCH_FEATURES                0x80000001
>
> +#define ARM_SMCCC_VERSION_1_0          0x10000
> +#define ARM_SMCCC_VERSION_1_1          0x10001
> +#define ARM_SMCCC_VERSION_1_2          0x10002
> +#define ARM_SMCCC_VERSION_1_3          0x10003
> +
>  #define ARM_SMCCC_RET_NOT_SUPPORTED    ((unsigned long)-1)
>
>  #ifndef __ASSEMBLY__
> --
> 2.39.2
>


-- 
Best regards - Freundliche Grüsse - Meilleures salutations

Igor Opaniuk
Senior Software Engineer, Embedded & Security
E: igor.opaniuk at foundries.io
W: www.foundries.io