drm/i915/lrc: Clarify the format of the context image

Not only the context image consist of two parts (the PPHWSP, and the
logical context state), but we also allocate a header at the start of
for sharing data with GuC. Thus every lrc looks like this:

  | [guc]          | [hwsp] [logical state] |
  |<- our header ->|<- context image      ->|

So far, we have oversimplified whenever we use each of these parts of the
context, just because the GuC header happens to be in page 0, and the
(PP)HWSP is in page 1. But this had led to using the same define for more
than one meaning (as a page index in the lrc and as 1 page).

This patch adds defines for the GuC shared page, the PPHWSP page and the
start of the logical state. It also updated the places where the old
define was being used. Since we are not changing the size (or format) of
the context, there are no functional changes.

v2: Use PPHWSP index for hws again.

Suggested-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Michel Thierry <michel.thierry@intel.com>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com>
Cc: Michal Wajdeczko <michal.wajdeczko@intel.com>
Cc: Oscar Mateo <oscar.mateo@intel.com>
Cc: intel-gvt-dev@lists.freedesktop.org
Link: http://patchwork.freedesktop.org/patch/msgid/20170712193032.27080-1-michel.thierry@intel.com
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: https://patchwork.freedesktop.org/patch/msgid/20170913085605.18299-1-chris@chris-wilson.co.uk

1 files changed, 22 insertions, 3 deletions

diff --git a/drivers/gpu/drm/i915/intel_lrc.h b/drivers/gpu/drm/i915/intel_lrc.h
index 3b1de327e504..314adee7127a 100644
--- a/drivers/gpu/drm/i915/intel_lrc.h
+++ b/drivers/gpu/drm/i915/intel_lrc.h
@@ -70,10 +70,29 @@ int logical_xcs_ring_init(struct intel_engine_cs *engine);
 
 /* Logical Ring Contexts */
 
-/* One extra page is added before LRC for GuC as shared data */
+/*
+ * We allocate a header at the start of the context image for our own
+ * use, therefore the actual location of the logical state is offset
+ * from the start of the VMA. The layout is
+ *
+ * | [guc]          | [hwsp] [logical state] |
+ * |<- our header ->|<- context image      ->|
+ *
+ */
+/* The first page is used for sharing data with the GuC */
 #define LRC_GUCSHR_PN	(0)
-#define LRC_PPHWSP_PN	(LRC_GUCSHR_PN + 1)
-#define LRC_STATE_PN	(LRC_PPHWSP_PN + 1)
+#define LRC_GUCSHR_SZ	(1)
+/* At the start of the context image is its per-process HWS page */
+#define LRC_PPHWSP_PN	(LRC_GUCSHR_PN + LRC_GUCSHR_SZ)
+#define LRC_PPHWSP_SZ	(1)
+/* Finally we have the logical state for the context */
+#define LRC_STATE_PN	(LRC_PPHWSP_PN + LRC_PPHWSP_SZ)
+
+/*
+ * Currently we include the PPHWSP in __intel_engine_context_size() so
+ * the size of the header is synonymous with the start of the PPHWSP.
+ */
+#define LRC_HEADER_PAGES LRC_PPHWSP_PN
 
 struct drm_i915_private;
 struct i915_gem_context;