[PATCH v6 17/25] drm/i915: Assign every HW context a unique ID

Chris Wilson
2016-04-26T20:06:54Z

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 <chris@chris-wilson.co.uk>
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com> #v2
---
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(-)

diff --git a/drivers/gpu/drm/i915/i915_debugfs.c b/drivers/gpu/drm/i915/i915_debugfs.c
index 4950d05d2948..3bd2f89933ff 100644
--- a/drivers/gpu/drm/i915/i915_debugfs.c
+++ b/drivers/gpu/drm/i915/i915_debugfs.c
@@ -2001,7 +2001,7 @@ static int i915_context_status(struct seq_file *m, void *unused)
ctx->legacy_hw_ctx.rcs_state == NULL)
continue;

- seq_puts(m, "HW context ");
+ seq_printf(m, "HW context %u ", ctx->hw_id);
describe_ctx(m, ctx);
if (ctx == dev_priv->kernel_context)
seq_printf(m, "(kernel context) ");
diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
index 831da9f43324..0f7575252c6e 100644
--- a/drivers/gpu/drm/i915/i915_drv.h
+++ b/drivers/gpu/drm/i915/i915_drv.h
@@ -851,6 +851,9 @@ struct intel_context {
struct i915_ctx_hang_stats hang_stats;
struct i915_hw_ppgtt *ppgtt;

+ /* Unique identifier for this context, used by the hw for tracking */
+ unsigned hw_id;
+
/* Legacy ring buffer submission */
struct {
struct drm_i915_gem_object *rcs_state;
@@ -1838,6 +1841,13 @@ struct drm_i915_private {
DECLARE_HASHTABLE(mm_structs, 7);
struct mutex mm_lock;

+ /* The hw wants to have a stable context identifier for the lifetime
+ * of the context (for OA, PASID, faults, etc). This is limited
+ * in execlists to 21 bits.
+ */
+ struct ida context_hw_ida;
+#define MAX_CONTEXT_HW_ID (1<<21) /* exclusive */
+
/* Kernel Modesetting */

struct drm_crtc *plane_to_crtc_mapping[I915_MAX_PIPES];
diff --git a/drivers/gpu/drm/i915/i915_gem_context.c b/drivers/gpu/drm/i915/i915_gem_context.c
index 4071a0ec134a..9477af0fcb33 100644
--- a/drivers/gpu/drm/i915/i915_gem_context.c
+++ b/drivers/gpu/drm/i915/i915_gem_context.c
@@ -171,6 +171,8 @@ void i915_gem_context_free(struct kref *ctx_ref)
if (ctx->legacy_hw_ctx.rcs_state)
drm_gem_object_unreference(&ctx->legacy_hw_ctx.rcs_state->base);
list_del(&ctx->link);
+
+ ida_simple_remove(&ctx->i915->context_hw_ida, ctx->hw_id);
kfree(ctx);
}

@@ -211,6 +213,28 @@ i915_gem_alloc_context_obj(struct drm_device *dev, size_t size)
return obj;
}

+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);
+ if (ret < 0)
+ return ret;
+ }
+
+ *out = ret;
+ return 0;
+}
+
static struct intel_context *
__create_hw_context(struct drm_device *dev,
struct drm_i915_file_private *file_priv)
@@ -223,6 +247,12 @@ __create_hw_context(struct drm_device *dev,
if (ctx == NULL)
return ERR_PTR(-ENOMEM);

+ ret = assign_hw_id(dev_priv, &ctx->hw_id);
+ if (ret) {
+ kfree(ctx);
+ return ERR_PTR(ret);
+ }
+
kref_init(&ctx->ref);
list_add_tail(&ctx->link, &dev_priv->context_list);
ctx->i915 = dev_priv;
@@ -366,6 +396,10 @@ int i915_gem_context_init(struct drm_device *dev)
}
}

+ /* Using the simple ida interface, the max is limited by sizeof(int) */
+ BUILD_BUG_ON(MAX_CONTEXT_HW_ID > INT_MAX);
+ ida_init(&dev_priv->context_hw_ida);
+
if (i915.enable_execlists) {
/* NB: intentionally left blank. We will allocate our own
* backing objects as we need them, thank you very much */
@@ -429,6 +463,8 @@ void i915_gem_context_fini(struct drm_device *dev)

i915_gem_context_unreference(dctx);
dev_priv->kernel_context = NULL;
+
+ ida_destroy(&dev_priv->context_hw_ida);
}

static int context_idr_cleanup(int id, void *p, void *data)