i965: Query whether we have kernel support for the TIMESTAMP register once

Move the query for the TIMESTAMP register from context init to the
screen, so that it is only queried once for all contexts.

On 32bit systems, some old kernels trigger a hw bug resulting in the
TIMESTAMP register being shifted and the low 32bits always zero. Detect
this by repeating the read a few times and check the register is
incrementing every 80ns as expected and not stuck on zero (as would be
the case with the buggy kernel/hw.).

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Martin Peres <martin.peres@linux.intel.com>
Reviewed-by: Martin Peres <martin.peres@linux.intel.com>
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>

src/mesa/drivers/dri/i965/intel_extensions.c

@@ -282,8 +282,6 @@ intelInitExtensions(struct gl_context *ctx)
    }
 
    if (brw->gen >= 6) {
-      uint64_t dummy;
-
       ctx->Extensions.ARB_blend_func_extended =
          !driQueryOptionb(&brw->optionCache, "disable_blend_func_extended");
       ctx->Extensions.ARB_conditional_render_inverted = true;
@@ -307,9 +305,7 @@ intelInitExtensions(struct gl_context *ctx)
       ctx->Extensions.EXT_transform_feedback = true;
       ctx->Extensions.OES_depth_texture_cube_map = true;
 
-      /* Test if the kernel has the ioctl. */
-      if (drm_intel_reg_read(brw->bufmgr, TIMESTAMP, &dummy) == 0)
-         ctx->Extensions.ARB_timer_query = true;
+      ctx->Extensions.ARB_timer_query = brw->intelScreen->hw_has_timestamp;
 
       /* Only enable this in core profile because other parts of Mesa behave
        * slightly differently when the extension is enabled.

src/mesa/drivers/dri/i965/intel_screen.c

@@ -1123,6 +1123,27 @@ intel_detect_swizzling(struct intel_screen *screen)
       return true;
 }
 
+static bool
+intel_detect_timestamp(struct intel_screen *screen)
+{
+   uint64_t dummy = 0;
+   int loop = 10;
+
+   /*
+    * On 32bit systems, some old kernels trigger a hw bug resulting in the
+    * TIMESTAMP register being shifted and the low 32bits always zero. Detect
+    * this by repeating the read a few times and check the register is
+    * incrementing every 80ns as expected and not stuck on zero (as would be
+    * the case with the buggy kernel/hw.).
+    */
+   do {
+      if (drm_intel_reg_read(screen->bufmgr, TIMESTAMP, &dummy))
+	 return false;
+   } while ((dummy & 0xffffffff) == 0 && --loop);
+
+   return loop > 0;
+}
+
 /**
  * Return array of MSAA modes supported by the hardware. The array is
  * zero-terminated and sorted in decreasing order.
@@ -1378,6 +1399,7 @@ __DRIconfig **intelInitScreen2(__DRIscreen *psp)
    intelScreen->hw_must_use_separate_stencil = intelScreen->devinfo->gen >= 7;
 
    intelScreen->hw_has_swizzling = intel_detect_swizzling(intelScreen);
+   intelScreen->hw_has_timestamp = intel_detect_timestamp(intelScreen);
 
    const char *force_msaa = getenv("INTEL_FORCE_MSAA");
    if (force_msaa) {

src/mesa/drivers/dri/i965/intel_screen.h

@@ -52,6 +52,8 @@ struct intel_screen
 
    bool hw_has_swizzling;
 
+   bool hw_has_timestamp;
+
    /**
     * Does the kernel support context reset notifications?
     */