drm/i915: add register read IOCTL

The interface's immediate purpose is to do synchronous timestamp queries
as required by GL_TIMESTAMP. The GPU has a register for reading the
timestamp but because that would normally require root access through
libpciaccess, the IOCTL can provide this service instead.

Currently the implementation whitelists only the render ring timestamp
register, because that is the only thing we need to expose at this time.

v2: make size implicit based on the register offset
Add a generation check

Reviewed-by: Eric Anholt <eric@anholt.net>
Cc: Jacek Lawrynowicz <jacek.lawrynowicz@intel.com>
Signed-off-by: Ben Widawsky <ben@bwidawsk.net>
[danvet: fixup the ioctl numerb:]
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

1 files changed, 7 insertions, 1 deletions

diff --git a/include/drm/i915_drm.h b/include/drm/i915_drm.h
index 95648ab819ac..b923b032743f 100644
--- a/include/drm/i915_drm.h
+++ b/include/drm/i915_drm.h
@@ -205,6 +205,7 @@ typedef struct _drm_i915_sarea {
 #define DRM_I915_GEM_CONTEXT_DESTROY    0x2e
 #define DRM_I915_GEM_SET_CACHEING       0x2f
 #define DRM_I915_GEM_GET_CACHEING       0x30
+#define DRM_I915_REG_READ               0x31
 
 #define DRM_IOCTL_I915_INIT             DRM_IOW( DRM_COMMAND_BASE + DRM_I915_INIT, drm_i915_init_t)
 #define DRM_IOCTL_I915_FLUSH            DRM_IO ( DRM_COMMAND_BASE + DRM_I915_FLUSH)
@@ -253,6 +254,7 @@ typedef struct _drm_i915_sarea {
 #define DRM_IOCTL_I915_GEM_WAIT         DRM_IOWR(DRM_COMMAND_BASE + DRM_I915_GEM_WAIT, struct drm_i915_gem_wait)
 #define DRM_IOCTL_I915_GEM_CONTEXT_CREATE       DRM_IOWR (DRM_COMMAND_BASE + DRM_I915_GEM_CONTEXT_CREATE, struct drm_i915_gem_context_create)
 #define DRM_IOCTL_I915_GEM_CONTEXT_DESTROY      DRM_IOW (DRM_COMMAND_BASE + DRM_I915_GEM_CONTEXT_DESTROY, struct drm_i915_gem_context_destroy)
+#define DRM_IOCTL_I915_REG_READ                 DRM_IOWR (DRM_COMMAND_BASE + DRM_I915_REG_READ, struct drm_i915_reg_read)
 
 /* Allow drivers to submit batchbuffers directly to hardware, relying
  * on the security mechanisms provided by hardware.
@@ -710,7 +712,7 @@ struct drm_i915_gem_busy {
 #define I915_CACHEING_CACHED            1
 
 struct drm_i915_gem_cacheing {
-        /** Handle of the buffer to check for busy */
+        /** Handle of the buffer to set/get the cacheing level of */
         __u32 handle;
 
         /** Cacheing level to apply or return value */
@@ -933,4 +935,8 @@ struct drm_i915_gem_context_destroy {
         __u32 pad;
 };
 
+struct drm_i915_reg_read {
+        __u64 offset;
+        __u64 val; /* Return value */
+};
 #endif                          /* _I915_DRM_H_ */