Re: [PATCH 22/55] drm/i915: Update deferred context creation to do explicit request management

[Tomas Elf <tomas.elf@intel.com>]

On 29/05/2015 17:43, John.C.Harrison@Intel.com wrote:
> From: John Harrison <John.C.Harrison@Intel.com>
>
> In execlist mode, context initialisation is deferred until first use of the
> given context. This is because execlist mode has per ring context state and thus
> many more context storage objects than legacy mode and many are never actually
> used. Previously, the initialisation commands were written to the ring and
> tagged with some random request structure via the OLR. This seemed to be causing
> a null pointer deference bug under certain circumstances (BZ:88865).
>
> This patch adds explicit request creation and submission to the deferred
> initialisation code path. Thus removing any reliance on or randomness caused by
> the OLR.
>
> Note that it should be possible to move the deferred context creation until even
> later - when the context is actually switched to rather than when it is merely
> validated. This would allow the initialisation to be done within the request of
> the work that is wanting to use the context. Hence, the extra request that is
> created, used and retired just for the context init could be removed completely.
> However, this is left for a follow up patch.
>
> For: VIZ-5115
> Signed-off-by: John Harrison <John.C.Harrison@Intel.com>
> ---
>   drivers/gpu/drm/i915/intel_lrc.c |   11 ++++++++++-
>   1 file changed, 10 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/i915/intel_lrc.c b/drivers/gpu/drm/i915/intel_lrc.c
> index 37efa93..2730efd 100644
> --- a/drivers/gpu/drm/i915/intel_lrc.c
> +++ b/drivers/gpu/drm/i915/intel_lrc.c
> @@ -1971,13 +1971,22 @@ int intel_lr_context_deferred_create(struct intel_context *ctx,
>   		lrc_setup_hardware_status_page(ring, ctx_obj);
>   	else if (ring->id == RCS && !ctx->rcs_initialized) {
>   		if (ring->init_context) {
> -			ret = ring->init_context(ring, ctx);
> +			struct drm_i915_gem_request *req;
> +
> +			ret = i915_gem_request_alloc(ring, ctx, &req);
> +			if (ret)
> +				return ret;
> +
> +			ret = ring->init_context(req->ring, ctx);
>   			if (ret) {
>   				DRM_ERROR("ring init context: %d\n", ret);
> +				i915_gem_request_cancel(req);
>   				ctx->engine[ring->id].ringbuf = NULL;
>   				ctx->engine[ring->id].state = NULL;
>   				goto error;
>   			}
> +
> +			i915_add_request_no_flush(req->ring);
>   		}
>
>   		ctx->rcs_initialized = true;
>

Reviewed-by: Tomas Elf <tomas.elf@intel.com>

Thanks,
Tomas

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