[Mesa-dev] [RFC 1/3] egl: Support IMG_context_priority

[Chris Wilson]

IMG_context_priority
https://www.khronos.org/registry/egl/extensions/IMG/EGL_IMG_context_priority.txt

    "This extension allows an EGLContext to be created with a priority
    hint. It is possible that an implementation will not honour the
    hint, especially if there are constraints on the number of high
    priority contexts available in the system, or system policy limits
    access to high priority contexts to appropriate system privilege
    level. A query is provided to find the real priority level assigned
    to the context after creation."

The extension adds a new eglCreateContext attribute for choosing a
priority hint. This stub parses the attribute and copies into the base
struct _egl_context, and hooks up the query similarly.

Since the attribute is purely a hint, I have no qualms about the lack of
implementation before reporting back the value the user gave!

Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
---
 src/egl/drivers/dri2/egl_dri2.c |  1 +
 src/egl/main/eglapi.c           |  2 ++
 src/egl/main/eglcontext.c       | 30 ++++++++++++++++++++++++++++++
 src/egl/main/eglcontext.h       |  1 +
 src/egl/main/egldisplay.h       |  2 ++
 5 files changed, 36 insertions(+)

diff --git a/src/egl/drivers/dri2/egl_dri2.c b/src/egl/drivers/dri2/egl_dri2.c
index d9e2ad7..5cd073e 100644
--- a/src/egl/drivers/dri2/egl_dri2.c
+++ b/src/egl/drivers/dri2/egl_dri2.c
@@ -638,6 +638,7 @@ dri2_setup_screen(_EGLDisplay *disp)
    assert(dri2_dpy->image_driver || dri2_dpy->dri2 || dri2_dpy->swrast);
    disp->Extensions.KHR_no_config_context = EGL_TRUE;
    disp->Extensions.KHR_surfaceless_context = EGL_TRUE;
+   disp->Extensions.IMG_context_priority = EGL_TRUE; /* only a hint */
 
    if (dri2_renderer_query_integer(dri2_dpy,
                                    __DRI2_RENDERER_HAS_FRAMEBUFFER_SRGB))
diff --git a/src/egl/main/eglapi.c b/src/egl/main/eglapi.c
index 04cac03..63705e6 100644
--- a/src/egl/main/eglapi.c
+++ b/src/egl/main/eglapi.c
@@ -483,6 +483,8 @@ _eglCreateExtensionsString(_EGLDisplay *dpy)
    _EGL_CHECK_EXTENSION(EXT_image_dma_buf_import);
    _EGL_CHECK_EXTENSION(EXT_swap_buffers_with_damage);
 
+   _EGL_CHECK_EXTENSION(IMG_context_priority);
+
    _EGL_CHECK_EXTENSION(KHR_cl_event2);
    _EGL_CHECK_EXTENSION(KHR_create_context);
    _EGL_CHECK_EXTENSION(KHR_fence_sync);
diff --git a/src/egl/main/eglcontext.c b/src/egl/main/eglcontext.c
index 60625f6..fe9fdaa 100644
--- a/src/egl/main/eglcontext.c
+++ b/src/egl/main/eglcontext.c
@@ -298,6 +298,33 @@ _eglParseContextAttribList(_EGLContext *ctx, _EGLDisplay *dpy,
             ctx->Flags |= EGL_CONTEXT_OPENGL_FORWARD_COMPATIBLE_BIT_KHR;
          break;
 
+      case EGL_CONTEXT_PRIORITY_LEVEL_IMG:
+         /* The  EGL_IMG_context_priority spec says:
+          *
+          * "EGL_CONTEXT_PRIORITY_LEVEL_IMG determines the priority level of
+          * the context to be created. This attribute is a hint, as an
+          * implementation may not support multiple contexts at some
+          * priority levels and system policy may limit access to high
+          * priority contexts to appropriate system privilege level. The
+          * default value for EGL_CONTEXT_PRIORITY_LEVEL_IMG is
+          * EGL_CONTEXT_PRIORITY_MEDIUM_IMG."
+          */
+         if (!dpy->Extensions.IMG_context_priority) {
+            err = EGL_BAD_ATTRIBUTE;
+            break;
+         }
+         switch (val) {
+         case EGL_CONTEXT_PRIORITY_HIGH_IMG:
+         case EGL_CONTEXT_PRIORITY_MEDIUM_IMG:
+         case EGL_CONTEXT_PRIORITY_LOW_IMG:
+            ctx->ContextPriority = val;
+            break;
+         default:
+            err = EGL_BAD_ATTRIBUTE;
+            break;
+         }
+         break;
+
       default:
          err = EGL_BAD_ATTRIBUTE;
          break;
@@ -556,6 +583,9 @@ _eglQueryContext(_EGLDriver *drv, _EGLDisplay *dpy, _EGLContext *c,
    case EGL_RENDER_BUFFER:
       *value = _eglQueryContextRenderBuffer(c);
       break;
+   case EGL_CONTEXT_PRIORITY_LEVEL_IMG:
+      *value = c->ContextPriority;
+      break;
    default:
       return _eglError(EGL_BAD_ATTRIBUTE, "eglQueryContext");
    }
diff --git a/src/egl/main/eglcontext.h b/src/egl/main/eglcontext.h
index 69bf77d..ea57b77 100644
--- a/src/egl/main/eglcontext.h
+++ b/src/egl/main/eglcontext.h
@@ -62,6 +62,7 @@ struct _egl_context
    EGLint Flags;
    EGLint Profile;
    EGLint ResetNotificationStrategy;
+   EGLint ContextPriority;
 
    /* The real render buffer when a window surface is bound */
    EGLint WindowRenderBuffer;
diff --git a/src/egl/main/egldisplay.h b/src/egl/main/egldisplay.h
index 62d9a11..a7f2f97 100644
--- a/src/egl/main/egldisplay.h
+++ b/src/egl/main/egldisplay.h
@@ -103,6 +103,8 @@ struct _egl_extensions
    EGLBoolean EXT_image_dma_buf_import;
    EGLBoolean EXT_swap_buffers_with_damage;
 
+   EGLBoolean IMG_context_priority;
+
    EGLBoolean KHR_cl_event2;
    EGLBoolean KHR_create_context;
    EGLBoolean KHR_fence_sync;
-- 
2.10.1