On 28/04/16 09:56, Chris Wilson wrote:
The hardware tracks contexts and expects all live contexts (those active
on the hardware) to have a unique identifier. This is used by the
hardware to assign pagefaults and the like to a particular context.

v2: Reorder to make sure ctx->link is not left dangling if the
assignment of a hw_id fails (Mika).

v3: We have 21bits of context space, not 20.

Signed-off-by: Chris Wilson <[email protected]>
Reviewed-by: Tvrtko Ursulin <[email protected]>
---
  drivers/gpu/drm/i915/i915_debugfs.c     |  2 +-
  drivers/gpu/drm/i915/i915_drv.h         | 10 +++++++++
  drivers/gpu/drm/i915/i915_gem_context.c | 36 +++++++++++++++++++++++++++++++++
  3 files changed, 47 insertions(+), 1 deletion(-)

[snip]

+static int assign_hw_id(struct drm_i915_private *dev_priv, unsigned *out)
+{
+       int ret;
+
+       ret = ida_simple_get(&dev_priv->context_hw_ida,
+                            0, MAX_CONTEXT_HW_ID, GFP_KERNEL);
+       if (ret < 0) {
+               /* Contexts are only released when no longer active.
+                * Flush any pending retires to hopefully release some
+                * stale contexts and try again.
+                */
+               i915_gem_retire_requests(dev_priv->dev);
+               ret = ida_simple_get(&dev_priv->context_hw_ida,
+                                    0, MAX_CONTEXT_HW_ID, GFP_KERNEL);

Should we once again reserve ID 0 to make it easier to identify things that have not yet been initialised properly?

.Dave.

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