Mesa (master): i965: Query whether we have kernel support for the TIMESTAMP register once

[Chris Wilson]

Module: Mesa
Branch: master
Commit: c8d3ebaffc0d7d915c1c19d54dba61fd1e57b338
URL:    http://cgit.freedesktop.org/mesa/mesa/commit/?id=c8d3ebaffc0d7d915c1c19d54dba61fd1e57b338

Author: Chris Wilson <chris at chris-wilson.co.uk>
Date:   Wed Apr 29 13:32:38 2015 +0100

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

---

 src/mesa/drivers/dri/i965/intel_extensions.c |    6 +-----
 src/mesa/drivers/dri/i965/intel_screen.c     |   22 ++++++++++++++++++++++
 src/mesa/drivers/dri/i965/intel_screen.h     |    2 ++
 3 files changed, 25 insertions(+), 5 deletions(-)

diff --git a/src/mesa/drivers/dri/i965/intel_extensions.c b/src/mesa/drivers/dri/i965/intel_extensions.c
index 3423190..740ac81 100644
--- a/src/mesa/drivers/dri/i965/intel_extensions.c
+++ b/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.
diff --git a/src/mesa/drivers/dri/i965/intel_screen.c b/src/mesa/drivers/dri/i965/intel_screen.c
index f9398d7..c0f5c92 100644
--- a/src/mesa/drivers/dri/i965/intel_screen.c
+++ b/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) {
diff --git a/src/mesa/drivers/dri/i965/intel_screen.h b/src/mesa/drivers/dri/i965/intel_screen.h
index 742b3d3..941e0fc 100644
--- a/src/mesa/drivers/dri/i965/intel_screen.h
+++ b/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?
     */