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

Hello Weizhao,

On Fri, Feb 2, 2024 at 4:43 AM Weizhao Ouyang o451686892@gmail.com wrote:

Hi Igor,

On Thu, Feb 1, 2024 at 10:36 PM Igor Opaniuk igor.opaniuk@foundries.io wrote:

...

Hello Weizhao,

On Wed, Jan 31, 2024 at 3:15 PM Weizhao Ouyang o451686892@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@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

Thanks for your review. The 9 Appendix B describes an approach to discovery the maximize ability without causing unsafe behavior on existing platforms. Regarding the second step, it is just using SMCCC_ARCH_WORKAROUND_1 as an example to test SMCCC_ARCH_FEATURES.

For the U-Boot case, we can revisit this from two perspectives:

1. SMCCC_ARCH_FEATURES is MANDATORY from SMCCC v1.1.
2. SMCCC_VERSION is OPTIONAL for SMCCC v1.0, so we should consider a

safe behavior. 3. U-Boot is using CONFIG_ARM_SMCCC_FEATURES to probe and bind SMCCC service driver if this driver is reported as supported. 4. U-Boot SMCCC service driver can embed its discovery process in is_supported() callback.

So now we can choose the following approach in U-Boot:

• Use firmware data (check "arm,psci-1.0") to determine whether a PSCI

implementation is present.

• Use PSCI_VERSION (psci_0_2_get_version() major version >= 0) to learn

whether PSCI_FEATURES is provided.

• Use PSCI_FEATURES with the SMCCC_VERSION Function Identifier as a

parameter to determine that SMCCC_VERSION is implemented.

• Use SMCCC_VERSION to learn whether the calling convention complies to

version 1.1 or above.

• Trying to probe and bind SMCCC service driver.

Thanks for the detailed explanation! Reviewed-by: Igor Opaniuk igor.opaniuk@foundries.io

BR, Weizhao

...

...

    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@foundries.io W: www.foundries.io