egl: Support IMG_context_priority

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!

v2: Remember to set the default ContextPriority value to medium.
v3: Use the driRendererQuery interface to probe the backend for
supported priority values and use those to mask the EGL interface.
v4: Treat the priority attrib as a hint and gracefully mask any requests
not supported by the driver, the EGLContext will remain at medium
priority.

Signed-off-by: Chris Wilson <[email protected]>
Cc: Rob Clark <[email protected]>
Reviewed-by: Ben Widawsky <[email protected]>
Reviewed-by: Emil Velikov <[email protected]>
Reviewed-by: Eric Engestrom <[email protected]>
Reviewed-by: Kenneth Graunke <[email protected]>

5 files changed, 71 insertions, 0 deletions

diff --git a/src/egl/drivers/dri2/egl_dri2.c b/src/egl/drivers/dri2/egl_dri2.c
index d7a88b29844..e18e05e4a99 100644
--- a/src/egl/drivers/dri2/egl_dri2.c
+++ b/src/egl/drivers/dri2/egl_dri2.c
@@ -687,6 +687,11 @@ dri2_setup_screen(_EGLDisplay *disp)
    disp->Extensions.KHR_no_config_context = EGL_TRUE;
    disp->Extensions.KHR_surfaceless_context = EGL_TRUE;
 
+   /* Report back to EGL the bitmask of priorities supported */
+   disp->Extensions.IMG_context_priority =
+      dri2_renderer_query_integer(dri2_dpy,
+                                  __DRI2_RENDERER_HAS_CONTEXT_PRIORITY);
+
    if (dri2_renderer_query_integer(dri2_dpy,
                                    __DRI2_RENDERER_HAS_FRAMEBUFFER_SRGB))
       disp->Extensions.KHR_gl_colorspace = EGL_TRUE;
diff --git a/src/egl/main/eglapi.c b/src/egl/main/eglapi.c
index 38fc9311cb8..215332f99cb 100644
--- a/src/egl/main/eglapi.c
+++ b/src/egl/main/eglapi.c
@@ -490,6 +490,8 @@ _eglCreateExtensionsString(_EGLDisplay *dpy)
    _EGL_CHECK_EXTENSION(EXT_image_dma_buf_import_modifiers);
    _EGL_CHECK_EXTENSION(EXT_swap_buffers_with_damage);
 
+   _EGL_CHECK_EXTENSION(IMG_context_priority);
+
    _EGL_CHECK_EXTENSION(KHR_cl_event2);
    _EGL_CHECK_EXTENSION(KHR_config_attribs);
    _EGL_CHECK_EXTENSION(KHR_create_context);
diff --git a/src/egl/main/eglcontext.c b/src/egl/main/eglcontext.c
index 1b03160439a..8c64f9ab82e 100644
--- a/src/egl/main/eglcontext.c
+++ b/src/egl/main/eglcontext.c
@@ -332,6 +332,60 @@ _eglParseContextAttribList(_EGLContext *ctx, _EGLDisplay *dpy,
          ctx->NoError = !!val;
          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."
+          */
+         {
+            int bit;
+
+            switch (val) {
+            case EGL_CONTEXT_PRIORITY_HIGH_IMG:
+               bit = __EGL_CONTEXT_PRIORITY_HIGH_BIT;
+               break;
+            case EGL_CONTEXT_PRIORITY_MEDIUM_IMG:
+               bit = __EGL_CONTEXT_PRIORITY_MEDIUM_BIT;
+               break;
+            case EGL_CONTEXT_PRIORITY_LOW_IMG:
+               bit = __EGL_CONTEXT_PRIORITY_LOW_BIT;
+               break;
+            default:
+               bit = -1;
+               break;
+            }
+
+            if (bit < 0) {
+               err = EGL_BAD_ATTRIBUTE;
+               break;
+            }
+
+            /* "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."
+             *
+             * We currently assume that the driver applies the priority hint
+             * and filters out any it cannot handle during the screen setup,
+             * e.g. dri2_setup_screen(). As such we can mask any change that
+             * the driver would fail, and ctx->ContextPriority matches the
+             * hint applied to the driver/hardware backend.
+             */
+            if (dpy->Extensions.IMG_context_priority & (1 << bit))
+               ctx->ContextPriority = val;
+
+            break;
+         }
+
       default:
          err = EGL_BAD_ATTRIBUTE;
          break;
@@ -533,6 +587,7 @@ _eglInitContext(_EGLContext *ctx, _EGLDisplay *dpy, _EGLConfig *conf,
    ctx->Flags = 0;
    ctx->Profile = EGL_CONTEXT_OPENGL_CORE_PROFILE_BIT_KHR;
    ctx->ResetNotificationStrategy = EGL_NO_RESET_NOTIFICATION_KHR;
+   ctx->ContextPriority = EGL_CONTEXT_PRIORITY_MEDIUM_IMG;
 
    err = _eglParseContextAttribList(ctx, dpy, attrib_list);
    if (err == EGL_SUCCESS && ctx->Config) {
@@ -598,6 +653,9 @@ _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 0667622ba15..a7523683136 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;
    EGLBoolean NoError;
 
    /* The real render buffer when a window surface is bound */
diff --git a/src/egl/main/egldisplay.h b/src/egl/main/egldisplay.h
index da5339b7bf9..952bfe53f00 100644
--- a/src/egl/main/egldisplay.h
+++ b/src/egl/main/egldisplay.h
@@ -105,6 +105,11 @@ struct _egl_extensions
    EGLBoolean EXT_image_dma_buf_import_modifiers;
    EGLBoolean EXT_swap_buffers_with_damage;
 
+   unsigned int IMG_context_priority;
+#define  __EGL_CONTEXT_PRIORITY_LOW_BIT    0
+#define  __EGL_CONTEXT_PRIORITY_MEDIUM_BIT 1
+#define  __EGL_CONTEXT_PRIORITY_HIGH_BIT   2
+
    EGLBoolean KHR_cl_event2;
    EGLBoolean KHR_config_attribs;
    EGLBoolean KHR_create_context;