Re: [CI 17/25] drm/i915: Assign every HW context a unique ID

[Dave Gordon <david.s.gordon@intel.com>]

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 <chris@chris-wilson.co.uk>
> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
> ---
>   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 +		/* Contexts are only released when no longer active.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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