Re: [PATCH] drm/i915: Android sync points for i915

[Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>]

Hi Jesse,

On 07/31/2014 07:58 PM, Jesse Barnes wrote:
> Expose an ioctl to create Android fences based on the Android sync point
> infrastructure (which in turn is based on DMA-buf fences).  Just a
> sketch at this point, no testing has been done.
>
> There are a couple of goals here:
>    1) allow applications and libraries to create fences without an
>       associated buffer
>    2) re-use a common API so userspace doesn't have to impedance mismatch
>       between different driver implementations too much
>    3) allow applications and libraries to use explicit synchronization if
>       they choose by exposing fences directly
>
> Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>

[snip]

> +
> +/*
> + * i915 fences on sync timelines
> + *
> + * We implement sync points in terms of i915 seqnos.  They're exposed
> + * through the new DRM_I915_GEM_FENCE ioctl, and can be mixed and matched
> + * with other Android timelines and aggregated into sync_fences, etc.
> + *
> + * TODO:
> + *   rebase on top of Chris's seqno/request stuff and use requests
> + *   allow non-RCS fences (need ring/context association)
> + */
> +
> +struct i915_sync_timeline {
> +	struct sync_timeline obj;
> +	struct intel_engine_cs *ring;
> +	struct drm_i915_private *dev_priv;
> +};
> +
> +struct i915_sync_pt {
> +	struct sync_pt pt;
> +	u32 seqno;
> +};

In case one day more than seqno needs to be exported to userspace, 
perhaps it would be handy to version the driver data somehow to allow 
for some forward/backward compatibility? Unless kernel/libdrm are 
supposed to be updated in lock-step already.

Regards,

Tvrtko