diff mbox series

[v3,4/4] API to verify the STOP API and image compatibility

Message ID 5ab3ddf0e16836620eef8f317345feca10f151a8.1581048597.git.psampat@linux.ibm.com
State Changes Requested
Headers show
Series Support for Self Save API in OPAL | expand

Checks

Context Check Description
snowpatch_ozlabs/apply_patch success Successfully applied on branch master (179d53dfcca30436777b0c748d530a979bbc8a45)
snowpatch_ozlabs/snowpatch_job_snowpatch-skiboot success Test snowpatch/job/snowpatch-skiboot on branch master
snowpatch_ozlabs/snowpatch_job_snowpatch-skiboot-dco fail Signed-off-by missing

Commit Message

Pratik R. Sampat Feb. 7, 2020, 4:20 a.m. UTC 
From: Prem Shanker Jha <premjha2@in.ibm.com>

Commit defines a new API primarily intended for OPAL to determine
cpu register save API's compatibility with HOMER layout and
self save restore. It can help OPAL determine if version of
API integrated with OPAL is different from hostboot.

This is used in the context of identifying support for self save in the
firmware. In the case the version of the firmware is older then we
simply cut support for the feature in the device tree rather than
catching the failure when the call is made.

Change-Id: Ic0de45a336cfb8b6b6096a10ac1cd3ffbaa44fc0
Reviewed-on: http://rchgit01.rchland.ibm.com/gerrit1/77612
Tested-by: FSP CI Jenkins <fsp-CI-jenkins+hostboot@us.ibm.com>
Tested-by: Jenkins Server <pfd-jenkins+hostboot@us.ibm.com>
Tested-by: Hostboot CI <hostboot-ci+hostboot@us.ibm.com>
Reviewed-by: RANGANATHPRASAD G. BRAHMASAMUDRA <prasadbgr@in.ibm.com>
Reviewed-by: Gregory S Still <stillgs@us.ibm.com>
Reviewed-by: Jennifer A Stofer <stofer@us.ibm.com>
Reviewed-on: http://rchgit01.rchland.ibm.com/gerrit1/77614
Tested-by: Jenkins OP Build CI <op-jenkins+hostboot@us.ibm.com>
Tested-by: Jenkins OP HW <op-hw-jenkins+hostboot@us.ibm.com>
Reviewed-by: Daniel M Crowell <dcrowell@us.ibm.com>
Signed-off-by: Pratik Rajesh Sampat <psampat@linux.ibm.com>

Co-authored-by: Prem Shanker Jha <premjha2@in.ibm.com>
Co-authored-by: Pratik Rajesh Sampat <psampat@linux.ibm.com>
---
 hw/slw.c                                 | 22 ++++++++-
 include/p9_stop_api.H                    | 26 ++++++++++
 libpore/p9_cpu_reg_restore_instruction.H |  7 ++-
 libpore/p9_hcd_memmap_base.H             |  7 +++
 libpore/p9_stop_api.C                    | 60 +++++++++++++++++++++++-
 libpore/p9_stop_api.H                    | 26 +++++++++-
 6 files changed, 143 insertions(+), 5 deletions(-)

Comments

Oliver O'Halloran Feb. 10, 2020, 1:38 a.m. UTC | #1 
On Fri, Feb 7, 2020 at 3:21 PM Pratik Rajesh Sampat
<psampat@linux.ibm.com> wrote:
>
> From: Prem Shanker Jha <premjha2@in.ibm.com>
>
> Commit defines a new API primarily intended for OPAL to determine
> cpu register save API's compatibility with HOMER layout and
> self save restore. It can help OPAL determine if version of
> API integrated with OPAL is different from hostboot.
>
> This is used in the context of identifying support for self save in the
> firmware. In the case the version of the firmware is older then we
> simply cut support for the feature in the device tree rather than
> catching the failure when the call is made.
>
> Change-Id: Ic0de45a336cfb8b6b6096a10ac1cd3ffbaa44fc0
> Reviewed-on: http://rchgit01.rchland.ibm.com/gerrit1/77612
> Tested-by: FSP CI Jenkins <fsp-CI-jenkins+hostboot@us.ibm.com>
> Tested-by: Jenkins Server <pfd-jenkins+hostboot@us.ibm.com>
> Tested-by: Hostboot CI <hostboot-ci+hostboot@us.ibm.com>
> Reviewed-by: RANGANATHPRASAD G. BRAHMASAMUDRA <prasadbgr@in.ibm.com>
> Reviewed-by: Gregory S Still <stillgs@us.ibm.com>
> Reviewed-by: Jennifer A Stofer <stofer@us.ibm.com>
> Reviewed-on: http://rchgit01.rchland.ibm.com/gerrit1/77614
> Tested-by: Jenkins OP Build CI <op-jenkins+hostboot@us.ibm.com>
> Tested-by: Jenkins OP HW <op-hw-jenkins+hostboot@us.ibm.com>
> Reviewed-by: Daniel M Crowell <dcrowell@us.ibm.com>
> Signed-off-by: Pratik Rajesh Sampat <psampat@linux.ibm.com>
>
> Co-authored-by: Prem Shanker Jha <premjha2@in.ibm.com>
> Co-authored-by: Pratik Rajesh Sampat <psampat@linux.ibm.com>

There is a bisect hazard between patch 3 (where self-save is added)
and patch 4 (where we check if it's supported). IMO, best way to
resolve this would be:

1. Take the slw.c changes out of this patch and move them into the current 3/4.
2. Re-order 3/4 and 4/4 so we add support for checking for support
before we add code to use it.


> ---
>  hw/slw.c                                 | 22 ++++++++-
>  include/p9_stop_api.H                    | 26 ++++++++++
>  libpore/p9_cpu_reg_restore_instruction.H |  7 ++-
>  libpore/p9_hcd_memmap_base.H             |  7 +++
>  libpore/p9_stop_api.C                    | 60 +++++++++++++++++++++++-
>  libpore/p9_stop_api.H                    | 26 +++++++++-
>  6 files changed, 143 insertions(+), 5 deletions(-)
>
> diff --git a/hw/slw.c b/hw/slw.c
> index 087a8619..95ba8dcd 100644
> --- a/hw/slw.c
> +++ b/hw/slw.c
> @@ -756,9 +756,12 @@ static void slw_late_init_p9(struct proc_chip *chip)
>  /* Add device tree properties to determine self-save | restore */
>  void add_cpu_self_save_properties()
>  {
> -       int i;
> +       int i, rc;
> +       bool self_save_supported = true;
>         struct dt_node *self_restore, *self_save, *power_mgt;
>         bitmap_t *self_restore_map, *self_save_map;
> +       uint64_t compVector = -1;
> +       struct proc_chip *chip;
>
>         const uint64_t self_restore_regs[] = {
>                 P8_SPR_HRMOR,
> @@ -791,6 +794,21 @@ void add_cpu_self_save_properties()
>         self_save_map = zalloc(BITMAP_BYTES(SPR_BITMAP_LENGTH));
>         self_restore_map = zalloc(BITMAP_BYTES(SPR_BITMAP_LENGTH));
>
> +       chip = next_chip(NULL);
> +       assert(chip);
> +       rc = proc_stop_api_discover_capability((void *) chip->homer_base,
> +                                              &compVector);
> +       if (rc == STOP_SAVE_ARG_INVALID_IMG) {
> +               prlog(PR_DEBUG, "HOMER BASE INVALID\n");
> +               goto bail;
> +       } else if (rc == STOP_SAVE_API_IMG_INCOMPATIBLE) {
> +               prlog(PR_DEBUG, "STOP API running incompatible versions\n");
> +               if ((compVector & SELF_RESTORE_VER_MISMATCH) == 0) {
> +                       prlog(PR_DEBUG, "Self-save API unsupported\n");
> +                       self_save_supported = false;
> +               }
> +       }
> +
>         for (i = 0; i < ARRAY_SIZE(self_save_regs); i++)
>                 bitmap_set_bit(*self_save_map, self_save_regs[i]);
>
> @@ -818,7 +836,7 @@ void add_cpu_self_save_properties()
>                 prerror("OCC: Failed to create self save node");
>                 goto bail;
>         }
> -       if (proc_gen == proc_gen_p9) {
> +       if (proc_gen == proc_gen_p9 && self_save_supported) {
>                 dt_add_property_string(self_save, "status", "enabled");
>
>                 dt_add_property(self_save, "sprn-bitmask", *self_save_map,
> diff --git a/include/p9_stop_api.H b/include/p9_stop_api.H
> index c304f70f..09ce3dc1 100644
> --- a/include/p9_stop_api.H
> +++ b/include/p9_stop_api.H
> @@ -110,6 +110,7 @@ typedef enum
>      STOP_SAVE_FAIL                       = 14,  // for internal failure within firmware.
>      STOP_SAVE_SPR_ENTRY_MISSING          =  15,
>      STOP_SAVE_SPR_BIT_POS_RESERVE        =  16,
> +    STOP_SAVE_API_IMG_INCOMPATIBLE       =  18,
>  } StopReturnCode_t;
>
>  /**
> @@ -164,6 +165,14 @@ typedef enum
>
>  } ScomSection_t;
>
> +/**
> + * @brief   versions pertaining relvant to STOP API.
> + */
> +typedef enum
> +{
> +    STOP_API_VER            =   0x00,
> +    STOP_API_VER_CONTROL    =   0x02,
> +} VersionList_t;
>
>
>  /**
> @@ -195,6 +204,14 @@ typedef enum
>      BIT_POS_USPRG1      =   30,
>  } SprBitPositionList_t;
>
> +typedef enum
> +{
> +    SMF_SUPPORT_MISSING_IN_HOMER         =   0x01,
> +    SELF_SUPPORT_MISSING_FOR_LE_HYP      =   0x02,
> +    IPL_RUNTIME_CPU_SAVE_VER_MISMATCH    =   0x04,
> +    SELF_RESTORE_VER_MISMATCH            =   0x08,
> +} VersionIncompList_t;
> +
>  #ifdef __cplusplus
>  extern "C" {
>  #endif
> @@ -247,6 +264,15 @@ StopReturnCode_t p9_stop_save_scom( void* const   i_pImage,
>  StopReturnCode_t
>  p9_stop_save_cpureg_control( void* i_pImage, const uint64_t i_pir,
>                               const uint32_t  i_saveRegVector );
> +
> +/**
> + * @brief       verifies if API is compatible of current HOMER image.
> + * @param[in]   i_pImage        points to the start of HOMER image of P9 chip.
> + * @param[out]  o_inCompVector  list of incompatibilities found.
> + * @return      STOP_SAVE_SUCCESS if if API succeeds, error code otherwise.
> + */
> +StopReturnCode_t proc_stop_api_discover_capability( void* const i_pImage, uint64_t* o_inCompVector );
> +
>  #ifdef __cplusplus
>  } // extern "C"
>  };  // namespace stopImageSection ends
> diff --git a/libpore/p9_cpu_reg_restore_instruction.H b/libpore/p9_cpu_reg_restore_instruction.H
> index d69a4212..5f168855 100644
> --- a/libpore/p9_cpu_reg_restore_instruction.H
> +++ b/libpore/p9_cpu_reg_restore_instruction.H
> @@ -5,7 +5,7 @@
>  /*                                                                        */
>  /* OpenPOWER HostBoot Project                                             */
>  /*                                                                        */
> -/* Contributors Listed Below - COPYRIGHT 2015,2018                        */
> +/* Contributors Listed Below - COPYRIGHT 2015,2020                        */
>  /* [+] International Business Machines Corp.                              */
>  /*                                                                        */
>  /*                                                                        */
> @@ -69,6 +69,11 @@ enum
>      OPCODE_18           =   18,
>      SELF_SAVE_FUNC_ADD  =   0x2300,
>      SELF_SAVE_OFFSET    =   0x180,
> +    SKIP_SPR_REST_INST  =   0x4800001c, //b . +0x01c
> +    MFLR_R30            =   0x7fc802a6,
> +    SKIP_SPR_SELF_SAVE  =   0x3bff0020, //addi r31 r31, 0x20
> +    MTLR_INST           =   0x7fc803a6,  //mtlr r30
> +    BRANCH_BE_INST      =   0x48000020,
>  };
>
>  #define MR_R0_TO_R10            0x7c0a0378UL //mr r10 r0
> diff --git a/libpore/p9_hcd_memmap_base.H b/libpore/p9_hcd_memmap_base.H
> index 000fafef..ddb56728 100644
> --- a/libpore/p9_hcd_memmap_base.H
> +++ b/libpore/p9_hcd_memmap_base.H
> @@ -444,6 +444,13 @@ HCD_CONST(CME_QUAD_PSTATE_SIZE,                 HALF_KB)
>
>  HCD_CONST(CME_REGION_SIZE,                      (64 * ONE_KB))
>
> +
> +// HOMER compatibility
> +
> +HCD_CONST(STOP_API_CPU_SAVE_VER,                0x02)
> +HCD_CONST(SELF_SAVE_RESTORE_VER,                0x02)
> +HCD_CONST(SMF_SUPPORT_SIGNATURE_OFFSET,         0x1300)
> +HCD_CONST(SMF_SELF_SIGNATURE,                   (0x5f534d46))
>  // Debug
>
>  HCD_CONST(CPMR_TRACE_REGION_OFFSET,             (512 * ONE_KB))
> diff --git a/libpore/p9_stop_api.C b/libpore/p9_stop_api.C
> index 2d9bb549..74341cff 100644
> --- a/libpore/p9_stop_api.C
> +++ b/libpore/p9_stop_api.C
> @@ -5,7 +5,7 @@
>  /*                                                                        */
>  /* OpenPOWER HostBoot Project                                             */
>  /*                                                                        */
> -/* Contributors Listed Below - COPYRIGHT 2015,2018                        */
> +/* Contributors Listed Below - COPYRIGHT 2015,2020                        */
>  /* [+] International Business Machines Corp.                              */
>  /*                                                                        */
>  /*                                                                        */
> @@ -1828,6 +1828,64 @@ StopReturnCode_t proc_stop_init_self_save(  void* const i_pImage, const uint32_t
>      return l_rc;
>  }
>
> +StopReturnCode_t proc_stop_api_discover_capability( void* const i_pImage, uint64_t * o_inCompVector )
> +{
> +    StopReturnCode_t l_rc       =   STOP_SAVE_SUCCESS;
> +    uint64_t l_incompVector     =   0;
> +    uint32_t l_tempWord         =   0;
> +    *o_inCompVector             =   0;
> +
> +    do
> +    {
> +        if( !i_pImage )
> +        {
> +            l_rc    =   STOP_SAVE_ARG_INVALID_IMG;
> +            break;
> +        }
> +
> +        l_tempWord      =
> +                *(uint32_t*)((uint8_t*)i_pImage + CPMR_HOMER_OFFSET + SMF_SUPPORT_SIGNATURE_OFFSET);
> +
> +        if( l_tempWord != SWIZZLE_4_BYTE(SMF_SELF_SIGNATURE) )
> +        {
> +            l_incompVector  |=  SMF_SUPPORT_MISSING_IN_HOMER;
> +        }
> +
> +        l_tempWord      =   *(uint32_t *)((uint8_t *)i_pImage + CPMR_HOMER_OFFSET + CPMR_HEADER_SIZE );
> +
> +        if( l_tempWord != SWIZZLE_4_BYTE(BRANCH_BE_INST) )
> +        {
> +            l_incompVector  |=  SELF_SUPPORT_MISSING_FOR_LE_HYP;
> +        }
> +
> +        l_tempWord      =   *(uint8_t *)((uint8_t *)i_pImage + CPMR_HOMER_OFFSET + CPMR_SELF_RESTORE_VER_BYTE );
> +
> +        prlog(PR_EMERG, "SLW: self save ltemp: 0x%x\n", l_tempWord);
That should be PR_DEBUG at most.

> +        if( l_tempWord < SELF_SAVE_RESTORE_VER )
> +        {
> +            l_incompVector  |=  SELF_RESTORE_VER_MISMATCH;
> +        }
> +
> +        l_tempWord      =   *(uint8_t *)((uint8_t *)i_pImage + CPMR_HOMER_OFFSET + CPMR_STOP_API_VER_BYTE );
> +
> +        if( l_tempWord < STOP_API_CPU_SAVE_VER )
> +        {
> +            l_incompVector  |=  IPL_RUNTIME_CPU_SAVE_VER_MISMATCH;
> +        }
> +
> +        prlog(PR_EMERG, "SLW: Comp: 0x%llx\n", l_incompVector);
Same here.

> +        *o_inCompVector     =   l_incompVector;
> +
> +        if( l_incompVector )
> +        {
> +            l_rc    =  STOP_SAVE_API_IMG_INCOMPATIBLE;
> +        }
> +
> +    }while(0);
> +
> +    return l_rc;
> +}
> +
>  #ifdef __cplusplus
>  } //namespace stopImageSection ends
>
> diff --git a/libpore/p9_stop_api.H b/libpore/p9_stop_api.H
> index 3f6420ff..983a3845 100644
> --- a/libpore/p9_stop_api.H
> +++ b/libpore/p9_stop_api.H
> @@ -5,7 +5,7 @@
>  /*                                                                        */
>  /* OpenPOWER HostBoot Project                                             */
>  /*                                                                        */
> -/* Contributors Listed Below - COPYRIGHT 2015,2018                        */
> +/* Contributors Listed Below - COPYRIGHT 2015,2020                        */
>  /* [+] International Business Machines Corp.                              */
>  /*                                                                        */
>  /*                                                                        */
> @@ -114,6 +114,7 @@ typedef enum
>      STOP_SAVE_FAIL                       =  14,  // for internal failure within firmware.
>      STOP_SAVE_SPR_ENTRY_MISSING          =  15,
>      STOP_SAVE_SPR_BIT_POS_RESERVE        =  16,
> +    STOP_SAVE_API_IMG_INCOMPATIBLE       =  18,
>  } StopReturnCode_t;
>
>  /**
> @@ -198,6 +199,21 @@ typedef enum
>      BIT_POS_USPRG1      =   30,
>  } SprBitPositionList_t;
>
> +/**
> + * @brief   List of major incompatibilities between API version.
> + * @note    STOP APIs assumes a specific HOMER layout, certain
> + * level of CME-SGPE hcode and certain version of self-save restore
> + * binary. A mismatch can break STOP function.
> + */
> +
> +typedef enum
> +{
> +    SMF_SUPPORT_MISSING_IN_HOMER         =   0x01,
> +    SELF_SUPPORT_MISSING_FOR_LE_HYP      =   0x02,
> +    IPL_RUNTIME_CPU_SAVE_VER_MISMATCH    =   0x04,
> +    SELF_RESTORE_VER_MISMATCH            =   0x08,
> +} VersionIncompList_t;
> +
>
>  #ifdef __cplusplus
>  extern "C" {
> @@ -341,6 +357,14 @@ StopReturnCode_t proc_stop_save_cpureg(  void* const i_pImage,
>   */
>  StopReturnCode_t proc_stop_init_self_save(  void* const i_pImage, const uint32_t i_corePos );
>
> +/**
> + * @brief       verifies if API is compatible of current HOMER image.
> + * @param[in]   i_pImage        points to the start of HOMER image of P9 chip.
> + * @param[out]  o_inCompVector  list of incompatibilities found.
> + * @return      STOP_SAVE_SUCCESS if if API succeeds, error code otherwise.
> + */
> +StopReturnCode_t proc_stop_api_discover_capability( void* const i_pImage, uint64_t* o_inCompVector );
> +
>  #ifdef __cplusplus
>  } // extern "C"
>  };  // namespace stopImageSection ends
> --
> 2.24.1
>
> _______________________________________________
> Skiboot mailing list
> Skiboot@lists.ozlabs.org
> https://lists.ozlabs.org/listinfo/skiboot
Pratik R. Sampat Feb. 10, 2020, 5:43 a.m. UTC | #2 
On 10/02/20 7:08 am, Oliver O'Halloran wrote:
> On Fri, Feb 7, 2020 at 3:21 PM Pratik Rajesh Sampat
> <psampat@linux.ibm.com> wrote:
>> From: Prem Shanker Jha <premjha2@in.ibm.com>
>>
>> Commit defines a new API primarily intended for OPAL to determine
>> cpu register save API's compatibility with HOMER layout and
>> self save restore. It can help OPAL determine if version of
>> API integrated with OPAL is different from hostboot.
>>
>> This is used in the context of identifying support for self save in the
>> firmware. In the case the version of the firmware is older then we
>> simply cut support for the feature in the device tree rather than
>> catching the failure when the call is made.
>>
>> Change-Id: Ic0de45a336cfb8b6b6096a10ac1cd3ffbaa44fc0
>> Reviewed-on: http://rchgit01.rchland.ibm.com/gerrit1/77612
>> Tested-by: FSP CI Jenkins <fsp-CI-jenkins+hostboot@us.ibm.com>
>> Tested-by: Jenkins Server <pfd-jenkins+hostboot@us.ibm.com>
>> Tested-by: Hostboot CI <hostboot-ci+hostboot@us.ibm.com>
>> Reviewed-by: RANGANATHPRASAD G. BRAHMASAMUDRA <prasadbgr@in.ibm.com>
>> Reviewed-by: Gregory S Still <stillgs@us.ibm.com>
>> Reviewed-by: Jennifer A Stofer <stofer@us.ibm.com>
>> Reviewed-on: http://rchgit01.rchland.ibm.com/gerrit1/77614
>> Tested-by: Jenkins OP Build CI <op-jenkins+hostboot@us.ibm.com>
>> Tested-by: Jenkins OP HW <op-hw-jenkins+hostboot@us.ibm.com>
>> Reviewed-by: Daniel M Crowell <dcrowell@us.ibm.com>
>> Signed-off-by: Pratik Rajesh Sampat <psampat@linux.ibm.com>
>>
>> Co-authored-by: Prem Shanker Jha <premjha2@in.ibm.com>
>> Co-authored-by: Pratik Rajesh Sampat <psampat@linux.ibm.com>
> There is a bisect hazard between patch 3 (where self-save is added)
> and patch 4 (where we check if it's supported). IMO, best way to
> resolve this would be:
>
> 1. Take the slw.c changes out of this patch and move them into the current 3/4.
> 2. Re-order 3/4 and 4/4 so we add support for checking for support
> before we add code to use it.

Alright, that's a cleaner way to do things. I'll reorder them accordingly.
Thanks.

--

Pratik
diff mbox series

Patch

diff --git a/hw/slw.c b/hw/slw.c
index 087a8619..95ba8dcd 100644
--- a/hw/slw.c
+++ b/hw/slw.c
@@ -756,9 +756,12 @@  static void slw_late_init_p9(struct proc_chip *chip)
 /* Add device tree properties to determine self-save | restore */
 void add_cpu_self_save_properties()
 {
-	int i;
+	int i, rc;
+	bool self_save_supported = true;
 	struct dt_node *self_restore, *self_save, *power_mgt;
 	bitmap_t *self_restore_map, *self_save_map;
+	uint64_t compVector = -1;
+	struct proc_chip *chip;
 
 	const uint64_t self_restore_regs[] = {
 		P8_SPR_HRMOR,
@@ -791,6 +794,21 @@  void add_cpu_self_save_properties()
 	self_save_map = zalloc(BITMAP_BYTES(SPR_BITMAP_LENGTH));
 	self_restore_map = zalloc(BITMAP_BYTES(SPR_BITMAP_LENGTH));
 
+	chip = next_chip(NULL);
+	assert(chip);
+	rc = proc_stop_api_discover_capability((void *) chip->homer_base,
+					       &compVector);
+	if (rc == STOP_SAVE_ARG_INVALID_IMG) {
+		prlog(PR_DEBUG, "HOMER BASE INVALID\n");
+		goto bail;
+	} else if (rc == STOP_SAVE_API_IMG_INCOMPATIBLE) {
+		prlog(PR_DEBUG, "STOP API running incompatible versions\n");
+		if ((compVector & SELF_RESTORE_VER_MISMATCH) == 0) {
+			prlog(PR_DEBUG, "Self-save API unsupported\n");
+			self_save_supported = false;
+		}
+	}
+
 	for (i = 0; i < ARRAY_SIZE(self_save_regs); i++)
 		bitmap_set_bit(*self_save_map, self_save_regs[i]);
 
@@ -818,7 +836,7 @@  void add_cpu_self_save_properties()
 		prerror("OCC: Failed to create self save node");
 		goto bail;
 	}
-	if (proc_gen == proc_gen_p9) {
+	if (proc_gen == proc_gen_p9 && self_save_supported) {
 		dt_add_property_string(self_save, "status", "enabled");
 
 		dt_add_property(self_save, "sprn-bitmask", *self_save_map,
diff --git a/include/p9_stop_api.H b/include/p9_stop_api.H
index c304f70f..09ce3dc1 100644
--- a/include/p9_stop_api.H
+++ b/include/p9_stop_api.H
@@ -110,6 +110,7 @@  typedef enum
     STOP_SAVE_FAIL                       = 14,  // for internal failure within firmware.
     STOP_SAVE_SPR_ENTRY_MISSING          =  15,
     STOP_SAVE_SPR_BIT_POS_RESERVE        =  16,
+    STOP_SAVE_API_IMG_INCOMPATIBLE       =  18,
 } StopReturnCode_t;
 
 /**
@@ -164,6 +165,14 @@  typedef enum
 
 } ScomSection_t;
 
+/**
+ * @brief   versions pertaining relvant to STOP API.
+ */
+typedef enum
+{
+    STOP_API_VER            =   0x00,
+    STOP_API_VER_CONTROL    =   0x02,
+} VersionList_t;
 
 
 /**
@@ -195,6 +204,14 @@  typedef enum
     BIT_POS_USPRG1      =   30,
 } SprBitPositionList_t;
 
+typedef enum
+{
+    SMF_SUPPORT_MISSING_IN_HOMER         =   0x01,
+    SELF_SUPPORT_MISSING_FOR_LE_HYP      =   0x02,
+    IPL_RUNTIME_CPU_SAVE_VER_MISMATCH    =   0x04,
+    SELF_RESTORE_VER_MISMATCH            =   0x08,
+} VersionIncompList_t;
+
 #ifdef __cplusplus
 extern "C" {
 #endif
@@ -247,6 +264,15 @@  StopReturnCode_t p9_stop_save_scom( void* const   i_pImage,
 StopReturnCode_t
 p9_stop_save_cpureg_control( void* i_pImage, const uint64_t i_pir,
                              const uint32_t  i_saveRegVector );
+
+/**
+ * @brief       verifies if API is compatible of current HOMER image.
+ * @param[in]   i_pImage        points to the start of HOMER image of P9 chip.
+ * @param[out]  o_inCompVector  list of incompatibilities found.
+ * @return      STOP_SAVE_SUCCESS if if API succeeds, error code otherwise.
+ */
+StopReturnCode_t proc_stop_api_discover_capability( void* const i_pImage, uint64_t* o_inCompVector );
+
 #ifdef __cplusplus
 } // extern "C"
 };  // namespace stopImageSection ends
diff --git a/libpore/p9_cpu_reg_restore_instruction.H b/libpore/p9_cpu_reg_restore_instruction.H
index d69a4212..5f168855 100644
--- a/libpore/p9_cpu_reg_restore_instruction.H
+++ b/libpore/p9_cpu_reg_restore_instruction.H
@@ -5,7 +5,7 @@ 
 /*                                                                        */
 /* OpenPOWER HostBoot Project                                             */
 /*                                                                        */
-/* Contributors Listed Below - COPYRIGHT 2015,2018                        */
+/* Contributors Listed Below - COPYRIGHT 2015,2020                        */
 /* [+] International Business Machines Corp.                              */
 /*                                                                        */
 /*                                                                        */
@@ -69,6 +69,11 @@  enum
     OPCODE_18           =   18,
     SELF_SAVE_FUNC_ADD  =   0x2300,
     SELF_SAVE_OFFSET    =   0x180,
+    SKIP_SPR_REST_INST  =   0x4800001c, //b . +0x01c
+    MFLR_R30            =   0x7fc802a6,
+    SKIP_SPR_SELF_SAVE  =   0x3bff0020, //addi r31 r31, 0x20
+    MTLR_INST           =   0x7fc803a6,  //mtlr r30
+    BRANCH_BE_INST      =   0x48000020,
 };
 
 #define MR_R0_TO_R10            0x7c0a0378UL //mr r10 r0
diff --git a/libpore/p9_hcd_memmap_base.H b/libpore/p9_hcd_memmap_base.H
index 000fafef..ddb56728 100644
--- a/libpore/p9_hcd_memmap_base.H
+++ b/libpore/p9_hcd_memmap_base.H
@@ -444,6 +444,13 @@  HCD_CONST(CME_QUAD_PSTATE_SIZE,                 HALF_KB)
 
 HCD_CONST(CME_REGION_SIZE,                      (64 * ONE_KB))
 
+
+// HOMER compatibility
+
+HCD_CONST(STOP_API_CPU_SAVE_VER,                0x02)
+HCD_CONST(SELF_SAVE_RESTORE_VER,                0x02)
+HCD_CONST(SMF_SUPPORT_SIGNATURE_OFFSET,         0x1300)
+HCD_CONST(SMF_SELF_SIGNATURE,                   (0x5f534d46))
 // Debug
 
 HCD_CONST(CPMR_TRACE_REGION_OFFSET,             (512 * ONE_KB))
diff --git a/libpore/p9_stop_api.C b/libpore/p9_stop_api.C
index 2d9bb549..74341cff 100644
--- a/libpore/p9_stop_api.C
+++ b/libpore/p9_stop_api.C
@@ -5,7 +5,7 @@ 
 /*                                                                        */
 /* OpenPOWER HostBoot Project                                             */
 /*                                                                        */
-/* Contributors Listed Below - COPYRIGHT 2015,2018                        */
+/* Contributors Listed Below - COPYRIGHT 2015,2020                        */
 /* [+] International Business Machines Corp.                              */
 /*                                                                        */
 /*                                                                        */
@@ -1828,6 +1828,64 @@  StopReturnCode_t proc_stop_init_self_save(  void* const i_pImage, const uint32_t
     return l_rc;
 }
 
+StopReturnCode_t proc_stop_api_discover_capability( void* const i_pImage, uint64_t * o_inCompVector )
+{
+    StopReturnCode_t l_rc       =   STOP_SAVE_SUCCESS;
+    uint64_t l_incompVector     =   0;
+    uint32_t l_tempWord         =   0;
+    *o_inCompVector             =   0;
+
+    do
+    {
+        if( !i_pImage )
+        {
+            l_rc    =   STOP_SAVE_ARG_INVALID_IMG;
+            break;
+        }
+
+        l_tempWord      =
+                *(uint32_t*)((uint8_t*)i_pImage + CPMR_HOMER_OFFSET + SMF_SUPPORT_SIGNATURE_OFFSET);
+
+        if( l_tempWord != SWIZZLE_4_BYTE(SMF_SELF_SIGNATURE) )
+        {
+            l_incompVector  |=  SMF_SUPPORT_MISSING_IN_HOMER;
+        }
+
+        l_tempWord      =   *(uint32_t *)((uint8_t *)i_pImage + CPMR_HOMER_OFFSET + CPMR_HEADER_SIZE );
+
+        if( l_tempWord != SWIZZLE_4_BYTE(BRANCH_BE_INST) )
+        {
+            l_incompVector  |=  SELF_SUPPORT_MISSING_FOR_LE_HYP;
+        }
+
+        l_tempWord      =   *(uint8_t *)((uint8_t *)i_pImage + CPMR_HOMER_OFFSET + CPMR_SELF_RESTORE_VER_BYTE );
+
+        prlog(PR_EMERG, "SLW: self save ltemp: 0x%x\n", l_tempWord);
+        if( l_tempWord < SELF_SAVE_RESTORE_VER )
+        {
+            l_incompVector  |=  SELF_RESTORE_VER_MISMATCH;
+        }
+
+        l_tempWord      =   *(uint8_t *)((uint8_t *)i_pImage + CPMR_HOMER_OFFSET + CPMR_STOP_API_VER_BYTE );
+
+        if( l_tempWord < STOP_API_CPU_SAVE_VER )
+        {
+            l_incompVector  |=  IPL_RUNTIME_CPU_SAVE_VER_MISMATCH;
+        }
+
+        prlog(PR_EMERG, "SLW: Comp: 0x%llx\n", l_incompVector);
+        *o_inCompVector     =   l_incompVector;
+
+        if( l_incompVector )
+        {
+            l_rc    =  STOP_SAVE_API_IMG_INCOMPATIBLE;
+        }
+
+    }while(0);
+
+    return l_rc;
+}
+
 #ifdef __cplusplus
 } //namespace stopImageSection ends
 
diff --git a/libpore/p9_stop_api.H b/libpore/p9_stop_api.H
index 3f6420ff..983a3845 100644
--- a/libpore/p9_stop_api.H
+++ b/libpore/p9_stop_api.H
@@ -5,7 +5,7 @@ 
 /*                                                                        */
 /* OpenPOWER HostBoot Project                                             */
 /*                                                                        */
-/* Contributors Listed Below - COPYRIGHT 2015,2018                        */
+/* Contributors Listed Below - COPYRIGHT 2015,2020                        */
 /* [+] International Business Machines Corp.                              */
 /*                                                                        */
 /*                                                                        */
@@ -114,6 +114,7 @@  typedef enum
     STOP_SAVE_FAIL                       =  14,  // for internal failure within firmware.
     STOP_SAVE_SPR_ENTRY_MISSING          =  15,
     STOP_SAVE_SPR_BIT_POS_RESERVE        =  16,
+    STOP_SAVE_API_IMG_INCOMPATIBLE       =  18,
 } StopReturnCode_t;
 
 /**
@@ -198,6 +199,21 @@  typedef enum
     BIT_POS_USPRG1      =   30,
 } SprBitPositionList_t;
 
+/**
+ * @brief   List of major incompatibilities between API version.
+ * @note    STOP APIs assumes a specific HOMER layout, certain
+ * level of CME-SGPE hcode and certain version of self-save restore
+ * binary. A mismatch can break STOP function.
+ */
+
+typedef enum
+{
+    SMF_SUPPORT_MISSING_IN_HOMER         =   0x01,
+    SELF_SUPPORT_MISSING_FOR_LE_HYP      =   0x02,
+    IPL_RUNTIME_CPU_SAVE_VER_MISMATCH    =   0x04,
+    SELF_RESTORE_VER_MISMATCH            =   0x08,
+} VersionIncompList_t;
+
 
 #ifdef __cplusplus
 extern "C" {
@@ -341,6 +357,14 @@  StopReturnCode_t proc_stop_save_cpureg(  void* const i_pImage,
  */
 StopReturnCode_t proc_stop_init_self_save(  void* const i_pImage, const uint32_t i_corePos );
 
+/**
+ * @brief       verifies if API is compatible of current HOMER image.
+ * @param[in]   i_pImage        points to the start of HOMER image of P9 chip.
+ * @param[out]  o_inCompVector  list of incompatibilities found.
+ * @return      STOP_SAVE_SUCCESS if if API succeeds, error code otherwise.
+ */
+StopReturnCode_t proc_stop_api_discover_capability( void* const i_pImage, uint64_t* o_inCompVector );
+
 #ifdef __cplusplus
 } // extern "C"
 };  // namespace stopImageSection ends