drm/i915: Record the position of the start of the request

Not only does it make for good documentation and debugging aide, but it is
also vital for when we want to unwind requests - such as when throwing away
an incomplete request.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: http://patchwork.freedesktop.org/patch/msgid/1470414607-32453-2-git-send-email-arun.siluvery@linux.intel.com
Reviewed-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1471254551-25805-1-git-send-email-chris@chris-wilson.co.uk

diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
index bf193ba1574e74ac45d18b92f37b73dbd48fe8a6..b1017950087ba39bab8e51268d0bf9e94c9b44c8 100644 (file)
--- a/drivers/gpu/drm/i915/i915_drv.h
+++ b/drivers/gpu/drm/i915/i915_drv.h
@@ -557,6 +557,7 @@ struct drm_i915_error_state {
                struct drm_i915_error_request {
                        long jiffies;
                        u32 seqno;
+                       u32 head;
                        u32 tail;
                } *requests;
 

diff --git a/drivers/gpu/drm/i915/i915_gem_request.c b/drivers/gpu/drm/i915/i915_gem_request.c
index b764c1d440c86f58fb414530b346763e5d4f0d46..8a9e9bfeea0934ef5801e89c92b821c4b9b4b667 100644 (file)
--- a/drivers/gpu/drm/i915/i915_gem_request.c
+++ b/drivers/gpu/drm/i915/i915_gem_request.c
@@ -426,6 +426,13 @@ i915_gem_request_alloc(struct intel_engine_cs *engine,
        if (ret)
                goto err_ctx;
 
+       /* Record the position of the start of the request so that
+        * should we detect the updated seqno part-way through the
+        * GPU processing the request, we never over-estimate the
+        * position of the head.
+        */
+       req->head = req->ring->tail;
+
        return req;
 
 err_ctx:
@@ -500,8 +507,6 @@ void __i915_add_request(struct drm_i915_gem_request *request, bool flush_caches)
 
        trace_i915_gem_request_add(request);
 
-       request->head = request_start;
-
        /* Seal the request and mark it as pending execution. Note that
         * we may inspect this state, without holding any locks, during
         * hangcheck. Hence we apply the barrier to ensure that we do not
@@ -514,10 +519,10 @@ void __i915_add_request(struct drm_i915_gem_request *request, bool flush_caches)
        list_add_tail(&request->link, &engine->request_list);
        list_add_tail(&request->ring_link, &ring->request_list);
 
-       /* Record the position of the start of the request so that
+       /* Record the position of the start of the breadcrumb so that
         * should we detect the updated seqno part-way through the
         * GPU processing the request, we never over-estimate the
-        * position of the head.
+        * position of the ring's HEAD.
         */
        request->postfix = ring->tail;
 

diff --git a/drivers/gpu/drm/i915/i915_gpu_error.c b/drivers/gpu/drm/i915/i915_gpu_error.c
index eecb87063c88f47e9cbeee356b362858b04702b7..d54848f5f2468114a91f4ffd9dd4de5d63c9f060 100644 (file)
--- a/drivers/gpu/drm/i915/i915_gpu_error.c
+++ b/drivers/gpu/drm/i915/i915_gpu_error.c
@@ -455,9 +455,10 @@ int i915_error_state_to_str(struct drm_i915_error_state_buf *m,
                                   dev_priv->engine[i].name,
                                   ee->num_requests);
                        for (j = 0; j < ee->num_requests; j++) {
-                               err_printf(m, "  seqno 0x%08x, emitted %ld, tail 0x%08x\n",
+                               err_printf(m, "  seqno 0x%08x, emitted %ld, head 0x%08x, tail 0x%08x\n",
                                           ee->requests[j].seqno,
                                           ee->requests[j].jiffies,
+                                          ee->requests[j].head,
                                           ee->requests[j].tail);
                        }
                }
@@ -1205,7 +1206,8 @@ static void i915_gem_record_rings(struct drm_i915_private *dev_priv,
                        erq = &ee->requests[count++];
                        erq->seqno = request->fence.seqno;
                        erq->jiffies = request->emitted_jiffies;
-                       erq->tail = request->postfix;
+                       erq->head = request->head;
+                       erq->tail = request->tail;
                }
        }
 }