Name

    IMG_pvric_end_to_end_signature

Name Strings

    GL_IMG_pvric_end_to_end_signature

Contact

    Deepak Ravikumar, Imagination Technologies 
    (deepak 'dot' ravikumar 'at' imgtec 'dot' com)
    
    Frank Bouwer, Imagination Technologies
    (frank 'dot' bouwer 'at' imgtec 'dot' com)

Contributors

    Ian King, Imagination Technologies
    (Ian 'dot' King 'at' imgtec 'dot' com)

    Deepak Ravikumar, Imagination Technologies 
    (deepak 'dot' ravikumar 'at' imgtec 'dot' com)

    Brajesh Gupta, Imagination Technologies 
    brajesh 'dot' gupta 'at' imgtec 'dot'com
    
    Amey Prabhu, Imagination Technologies
    amey 'dot' prabhu 'at' imgtec 'dot'com

Status

    Complete.

Version

    Last Modified Date: March 29, 2023
    Revision: 1.0

Number

    OpenGL SC Extension #2
 
Dependencies

    This extension is written against the OpenGL SC 2.0.1 
    specification, EGL Version 1.4 specification and the
    GLSL ES Shading Language 1.00 specification with limitations as 
    specified in Appendix F of the OpenGL SC 2.0.1 specification.
 
    IMG_tile_region_protection needs to be present for this extension
    to be implemented.

Overview

    This extension provides a safety signature mechanism
    for Imagination Technologies Power VR Image Compression (PVRIC), 
    that can be used to efficiently verify the integrity of the 
    compression and decompression done by PowerVR's PVRIC as well as the 
    corresponding memory accesses data paths, when processing 
    safety-related workloads, in the presence of potential faults.

    Application should use IMG_tile_region_protection extension to
    tag a workload as safety-related.

IP Status

    Imagination Technologies Proprietary

New Procedures and Functions

    None

New Types

    None

New Tokens

    Returned by GetError

    GL_PVRIC_SIGNATURE_MISMATCH_IMG         0x8EA3


Additions to Chapter 2 of the OpenGL SC 2.0.1 Specification
(OpenGL SC Operation)

    Section 2.5 GL Errors Add below to the value that can be returned 
    by GetError

    If a signature mismatch is detected by the PVRIC safety mechanism 
    while processing a safety-related workload, the error 
    PVRIC_SIGNATURE_MISMATCH_IMG is generated.

    Table 2.3 Summary of GL errors add the below entry
                                            
    Error                           Description         Offending 
                                                        command 
                                                        ignored?   Advisory Action
    -------------------             -----------         ------    ------------------- 
    PVRIC_SIGNATURE_MISMATCH_IMG    Signature           Yes        Abort for
                                    mismatch detected              safety
                                    during PVRIC                   renders.
                                    operation

 
Dependencies on GL and ES profiles, versions, and other extensions

    None
   
Errors

    PVRIC_SIGNATURE_MISMATCH_IMG error is generated if a signature
    mismatch is detected by the PVRIC safety mechanism when processing
    the safety-related workload

New State

    None

New Implementation Dependent State

    None

Sample Code

    /* Step 1 Tag all safety-related textures / render buffers to 
     *        GL before creating their storage 
     */
    glEnable(GL_TRP_IMG)
    glTexStorage2D(GL_TEXTURE_2D,
                   texture_levels,
                   GL_RGBA8,
                   texwidth,
                   texheight)
        
    if (error == (GLenum)GL_NO_ERROR)
    {
        glTexSubImage2D(GL_TEXTURE_2D,
                        0,
                        0,
                        0,
                        texwidth,
                        texheight,
                        GL_RGBA,
                        GL_UNSIGNED_BYTE,
                        texdata)
    }
    ...
    /* Create storage for safety-related render buffers */
    glRenderbufferStorage(GL_RENDERBUFFER, GL_RGB565, width, height)
    ...
    glDisable(GL_TRP_IMG)
    ...
    /* Create storage for non safety-related render buffers 
     * with TRP off
     */
    glRenderbufferStorage(GL_RENDERBUFFER, GL_RGB565, width, height)
    ...
    /* Step 2 Mark WLs as safety-related by enabling TRP */
    glEnable(GL_TRP_IMG);
    GLenum error = glGetError();
    if (error == (GLenum)GL_NO_ERROR)
    {
        /* Step 3 Submit commands for rendering the 
         * safety-related sequence of geometric primitives.
         */
        ...
    }
    /* Step 4  Upon completion of the submitted commands to GL,  
     * check status of the safety-related renders
     */
    error = glGetError();
    if (error != (GLenum)GL_NO_ERROR)
    {
       /*
        * Safety FAULT: Abort and initiate fault handling
        */
    }


Conformance Tests

    None

Issues

    1) How can application turn on the PVRIC signature mechanism for 
       its safety-related workloads?

        RESOLVED: From application perspective, it needs to use 
        IMG_tile_region_protection extension interface 
        glEnable(GL_TRP_IMG) to tag all its safety-related workloads. 
        Also, before creating storage using glTexStorage2D() for
        textures or glRenderbufferStorage() for render buffers  which 
        are safety-related, application should indicate to the GL that 
        it is safety-related by calling glEnable(GL_TRP_IMG).

        This extension efficiently enables PVRIC safety signature 
        verification for all safety workloads and safety-related
        resources such as textures and render buffers,  and informs the 
        application about any mismatch in signature verification, 
        so that, if a signature fault is reported, application can 
        act on it.

    2) How should application handle a PVRIC signature mismatch?

         RESOLVED: A PVRIC signature fault indicates that there was a 
         fault in either the compression / decompression or in the
         corresponding data path which has affected the integrity of the
         safety-related render. In this case, the safety render might be
         rendered incorrectly. It is hence recommended that the 
         application aborts this faulty render,
         recreates the safety-related resources such as textures, 
         render buffers and resubmits the safety-workload after any
         additional fault handling.

Revision History

      Revision 1.0, 29/03/2023 
      - Initial revision.