2. Arm SiP Services

This document enumerates and describes the Arm SiP (Silicon Provider) services.

SiP services are non-standard, platform-specific services offered by the silicon implementer or platform provider. They are accessed via SMC (“SMC calls”) instruction executed from Exception Levels below EL3. SMC calls for SiP services:

  • Follow SMC Calling Convention;

  • Use SMC function IDs that fall in the SiP range, which are 0xc2000000 - 0xc200ffff for 64-bit calls, and 0x82000000 - 0x8200ffff for 32-bit calls.

The Arm SiP implementation offers the following services:

  • Performance Measurement Framework (PMF)

  • Execution State Switching service

  • DebugFS interface

Source definitions for Arm SiP service are located in the arm_sip_svc.h header file.

2.1. Performance Measurement Framework (PMF)

The Performance Measurement Framework allows callers to retrieve timestamps captured at various paths in TF-A execution.

2.2. Execution State Switching service

Execution State Switching service provides a mechanism for a non-secure lower Exception Level (either EL2, or NS EL1 if EL2 isn’t implemented) to request to switch its execution state (a.k.a. Register Width), either from AArch64 to AArch32, or from AArch32 to AArch64, for the calling CPU. This service is only available when Trusted Firmware-A (TF-A) is built for AArch64 (i.e. when build option ARCH is set to aarch64).

2.2.1. ARM_SIP_SVC_EXE_STATE_SWITCH

Arguments:
    uint32_t Function ID
    uint32_t PC hi
    uint32_t PC lo
    uint32_t Cookie hi
    uint32_t Cookie lo

Return:
    uint32_t

The function ID parameter must be 0x82000020. It uniquely identifies the Execution State Switching service being requested.

The parameters PC hi and PC lo defines upper and lower words, respectively, of the entry point (physical address) at which execution should start, after Execution State has been switched. When calling from AArch64, PC hi must be 0.

When execution starts at the supplied entry point after Execution State has been switched, the parameters Cookie hi and Cookie lo are passed in CPU registers 0 and 1, respectively. When calling from AArch64, Cookie hi must be 0.

This call can only be made on the primary CPU, before any secondaries were brought up with CPU_ON PSCI call. Otherwise, the call will always fail.

The effect of switching execution state is as if the Exception Level were entered for the first time, following power on. This means CPU registers that have a defined reset value by the Architecture will assume that value. Other registers should not be expected to hold their values before the call was made. CPU endianness, however, is preserved from the previous execution state. Note that this switches the execution state of the calling CPU only. This is not a substitute for PSCI SYSTEM_RESET.

The service may return the following error codes:

  • STATE_SW_E_PARAM: If any of the parameters were deemed invalid for a specific request.

  • STATE_SW_E_DENIED: If the call is not successful, or when TF-A is built for AArch32.

If the call is successful, the caller wouldn’t observe the SMC returning. Instead, execution starts at the supplied entry point, with the CPU registers 0 and 1 populated with the supplied Cookie hi and Cookie lo values, respectively.

2.3. DebugFS interface

The optional DebugFS interface is accessed through an SMC SiP service. Refer to the component documentation for details.

String parameters are passed through a shared buffer using a specific union:

union debugfs_parms {
    struct {
        char fname[MAX_PATH_LEN];
    } open;

    struct mount {
        char srv[MAX_PATH_LEN];
        char where[MAX_PATH_LEN];
        char spec[MAX_PATH_LEN];
    } mount;

    struct {
        char path[MAX_PATH_LEN];
        dir_t dir;
    } stat;

    struct {
        char oldpath[MAX_PATH_LEN];
        char newpath[MAX_PATH_LEN];
    } bind;
};

Format of the dir_t structure as such:

typedef struct {
    char            name[NAMELEN];
    long            length;
    unsigned char   mode;
    unsigned char   index;
    unsigned char   dev;
    qid_t           qid;
} dir_t;
  • Identifiers

SMC_OK

0

SMC_UNK

-1

DEBUGFS_E_INVALID_PARAMS

-2

MOUNT

0

CREATE

1

OPEN

2

CLOSE

3

READ

4

WRITE

5

SEEK

6

BIND

7

STAT

8

INIT

10

VERSION

11

2.3.1. MOUNT

2.3.1.1. Description

This operation mounts a blob of data pointed to by path stored in src, at filesystem location pointed to by path stored in where, using driver pointed to by path in spec.

2.3.1.2. Parameters

uint32_t

FunctionID (0x82000030 / 0xC2000030)

uint32_t

MOUNT

2.3.1.3. Return values

int32_t

w0 == SMC_OK on success

w0 == DEBUGFS_E_INVALID_PARAMS if mount operation failed

2.3.2. OPEN

2.3.2.1. Description

This operation opens the file path pointed to by fname.

2.3.2.2. Parameters

uint32_t

FunctionID (0x82000030 / 0xC2000030)

uint32_t

OPEN

uint32_t

mode

mode can be one of:

enum mode {
    O_READ   = 1 << 0,
    O_WRITE  = 1 << 1,
    O_RDWR   = 1 << 2,
    O_BIND   = 1 << 3,
    O_DIR    = 1 << 4,
    O_STAT   = 1 << 5
};

2.3.2.3. Return values

int32_t

w0 == SMC_OK on success

w0 == DEBUGFS_E_INVALID_PARAMS if open operation failed

uint32_t

w1: file descriptor id on success.

2.3.3. CLOSE

2.3.3.1. Description

This operation closes a file described by a file descriptor obtained by a previous call to OPEN.

2.3.3.2. Parameters

uint32_t

FunctionID (0x82000030 / 0xC2000030)

uint32_t

CLOSE

uint32_t

File descriptor id returned by OPEN

2.3.3.3. Return values

int32_t

w0 == SMC_OK on success

w0 == DEBUGFS_E_INVALID_PARAMS if close operation failed

2.3.4. READ

2.3.4.1. Description

This operation reads a number of bytes from a file descriptor obtained by a previous call to OPEN.

2.3.4.2. Parameters

uint32_t

FunctionID (0x82000030 / 0xC2000030)

uint32_t

READ

uint32_t

File descriptor id returned by OPEN

uint32_t

Number of bytes to read

2.3.4.3. Return values

On success, the read data is retrieved from the shared buffer after the operation.

int32_t

w0 == SMC_OK on success

w0 == DEBUGFS_E_INVALID_PARAMS if read operation failed

uint32_t

w1: number of bytes read on success.

2.3.5. SEEK

2.3.5.1. Description

Move file pointer for file described by given file descriptor of given offset related to whence.

2.3.5.2. Parameters

uint32_t

FunctionID (0x82000030 / 0xC2000030)

uint32_t

SEEK

uint32_t

File descriptor id returned by OPEN

sint32_t

offset in the file relative to whence

uint32_t

whence

whence can be one of:

KSEEK_SET

0

KSEEK_CUR

1

KSEEK_END

2

2.3.5.3. Return values

int32_t

w0 == SMC_OK on success

w0 == DEBUGFS_E_INVALID_PARAMS if seek operation failed

2.3.6. BIND

2.3.6.1. Description

Create a link from oldpath to newpath.

2.3.6.2. Parameters

uint32_t

FunctionID (0x82000030 / 0xC2000030)

uint32_t

BIND

2.3.6.3. Return values

int32_t

w0 == SMC_OK on success

w0 == DEBUGFS_E_INVALID_PARAMS if bind operation failed

2.3.7. STAT

2.3.7.1. Description

Perform a stat operation on provided file name and returns the directory entry statistics into dir.

2.3.7.2. Parameters

uint32_t

FunctionID (0x82000030 / 0xC2000030)

uint32_t

STAT

2.3.7.3. Return values

int32_t

w0 == SMC_OK on success

w0 == DEBUGFS_E_INVALID_PARAMS if stat operation failed

2.3.8. INIT

2.3.8.1. Description

Initial call to setup the shared exchange buffer. Notice if successful once, subsequent calls fail after a first initialization. The caller maps the same page frame in its virtual space and uses this buffer to exchange string parameters with filesystem primitives.

2.3.8.2. Parameters

uint32_t

FunctionID (0x82000030 / 0xC2000030)

uint32_t

INIT

uint64_t

Physical address of the shared buffer.

2.3.8.3. Return values

int32_t

w0 == SMC_OK on success

w0 == DEBUGFS_E_INVALID_PARAMS if already initialized, or internal error occurred.

2.3.9. VERSION

2.3.9.1. Description

Returns the debugfs interface version if implemented in TF-A.

2.3.9.2. Parameters

uint32_t

FunctionID (0x82000030 / 0xC2000030)

uint32_t

VERSION

2.3.9.3. Return values

int32_t

w0 == SMC_OK on success

w0 == SMC_UNK if interface is not implemented

uint32_t

w1: On success, debugfs interface version, 32 bits value with major version number in upper 16 bits and minor version in lower 16 bits.

  • CREATE(1) and WRITE (5) command identifiers are unimplemented and return SMC_UNK.


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