drm/i915: Update to Linux 3.18

[dragonfly.git] / sys / dev / drm / i915 / i915_gem_context.c

/*
 * Copyright © 2011-2012 Intel Corporation
 *
 * Permission is hereby granted, free of charge, to any person obtaining a
 * copy of this software and associated documentation files (the "Software"),
 * to deal in the Software without restriction, including without limitation
 * the rights to use, copy, modify, merge, publish, distribute, sublicense,
 * and/or sell copies of the Software, and to permit persons to whom the
 * Software is furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice (including the next
 * paragraph) shall be included in all copies or substantial portions of the
 * Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
 * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
 * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
 * IN THE SOFTWARE.
 *
 * Authors:
 *    Ben Widawsky <ben@bwidawsk.net>
 *
 */

/*
 * This file implements HW context support. On gen5+ a HW context consists of an
 * opaque GPU object which is referenced at times of context saves and restores.
 * With RC6 enabled, the context is also referenced as the GPU enters and exists
 * from RC6 (GPU has it's own internal power context, except on gen5). Though
 * something like a context does exist for the media ring, the code only
 * supports contexts for the render ring.
 *
 * In software, there is a distinction between contexts created by the user,
 * and the default HW context. The default HW context is used by GPU clients
 * that do not request setup of their own hardware context. The default
 * context's state is never restored to help prevent programming errors. This
 * would happen if a client ran and piggy-backed off another clients GPU state.
 * The default context only exists to give the GPU some offset to load as the
 * current to invoke a save of the context we actually care about. In fact, the
 * code could likely be constructed, albeit in a more complicated fashion, to
 * never use the default context, though that limits the driver's ability to
 * swap out, and/or destroy other contexts.
 *
 * All other contexts are created as a request by the GPU client. These contexts
 * store GPU state, and thus allow GPU clients to not re-emit state (and
 * potentially query certain state) at any time. The kernel driver makes
 * certain that the appropriate commands are inserted.
 *
 * The context life cycle is semi-complicated in that context BOs may live
 * longer than the context itself because of the way the hardware, and object
 * tracking works. Below is a very crude representation of the state machine
 * describing the context life.
 *                                         refcount     pincount     active
 * S0: initial state                          0            0           0
 * S1: context created                        1            0           0
 * S2: context is currently running           2            1           X
 * S3: GPU referenced, but not current        2            0           1
 * S4: context is current, but destroyed      1            1           0
 * S5: like S3, but destroyed                 1            0           1
 *
 * The most common (but not all) transitions:
 * S0->S1: client creates a context
 * S1->S2: client submits execbuf with context
 * S2->S3: other clients submits execbuf with context
 * S3->S1: context object was retired
 * S3->S2: clients submits another execbuf
 * S2->S4: context destroy called with current context
 * S3->S5->S0: destroy path
 * S4->S5->S0: destroy path on current context
 *
 * There are two confusing terms used above:
 *  The "current context" means the context which is currently running on the
 *  GPU. The GPU has loaded its state already and has stored away the gtt
 *  offset of the BO. The GPU is not actively referencing the data at this
 *  offset, but it will on the next context switch. The only way to avoid this
 *  is to do a GPU reset.
 *
 *  An "active context' is one which was previously the "current context" and is
 *  on the active list waiting for the next context switch to occur. Until this
 *  happens, the object must remain at the same gtt offset. It is therefore
 *  possible to destroy a context, but it is still active.
 *
 */

#include <drm/drmP.h>
#include <drm/i915_drm.h>
#include "i915_drv.h"

/* This is a HW constraint. The value below is the largest known requirement
 * I've seen in a spec to date, and that was a workaround for a non-shipping
 * part. It should be safe to decrease this, but it's more future proof as is.
 */
#define GEN6_CONTEXT_ALIGN (64<<10)
#define GEN7_CONTEXT_ALIGN 4096

static size_t get_context_alignment(struct drm_device *dev)
{
        if (IS_GEN6(dev))
                return GEN6_CONTEXT_ALIGN;

        return GEN7_CONTEXT_ALIGN;
}

static int get_context_size(struct drm_device *dev)
{
        struct drm_i915_private *dev_priv = dev->dev_private;
        int ret;
        u32 reg;

        switch (INTEL_INFO(dev)->gen) {
        case 6:
                reg = I915_READ(CXT_SIZE);
                ret = GEN6_CXT_TOTAL_SIZE(reg) * 64;
                break;
        case 7:
                reg = I915_READ(GEN7_CXT_SIZE);
                if (IS_HASWELL(dev))
                        ret = HSW_CXT_TOTAL_SIZE;
                else
                        ret = GEN7_CXT_TOTAL_SIZE(reg) * 64;
                break;
        case 8:
                ret = GEN8_CXT_TOTAL_SIZE;
                break;
        default:
                BUG();
        }

        return ret;
}

void i915_gem_context_free(struct kref *ctx_ref)
{
        struct intel_context *ctx = container_of(ctx_ref,
                                                 typeof(*ctx), ref);

        if (i915.enable_execlists)
                intel_lr_context_free(ctx);

        i915_ppgtt_put(ctx->ppgtt);

        if (ctx->legacy_hw_ctx.rcs_state)
                drm_gem_object_unreference(&ctx->legacy_hw_ctx.rcs_state->base);
        list_del(&ctx->link);
        kfree(ctx);
}

struct drm_i915_gem_object *
i915_gem_alloc_context_obj(struct drm_device *dev, size_t size)
{
        struct drm_i915_gem_object *obj;
        int ret;

        obj = i915_gem_alloc_object(dev, size);
        if (obj == NULL)
                return ERR_PTR(-ENOMEM);

        /*
         * Try to make the context utilize L3 as well as LLC.
         *
         * On VLV we don't have L3 controls in the PTEs so we
         * shouldn't touch the cache level, especially as that
         * would make the object snooped which might have a
         * negative performance impact.
         */
        if (INTEL_INFO(dev)->gen >= 7 && !IS_VALLEYVIEW(dev)) {
                ret = i915_gem_object_set_cache_level(obj, I915_CACHE_L3_LLC);
                /* Failure shouldn't ever happen this early */
                if (WARN_ON(ret)) {
                        drm_gem_object_unreference(&obj->base);
                        return ERR_PTR(ret);
                }
        }

        return obj;
}

static struct intel_context *
__create_hw_context(struct drm_device *dev,
                    struct drm_i915_file_private *file_priv)
{
        struct drm_i915_private *dev_priv = dev->dev_private;
        struct intel_context *ctx;
        int ret;

        ctx = kzalloc(sizeof(*ctx), GFP_KERNEL);
        if (ctx == NULL)
                return ERR_PTR(-ENOMEM);

        kref_init(&ctx->ref);
        list_add_tail(&ctx->link, &dev_priv->context_list);

        if (dev_priv->hw_context_size) {
                struct drm_i915_gem_object *obj =
                                i915_gem_alloc_context_obj(dev, dev_priv->hw_context_size);
                if (IS_ERR(obj)) {
                        ret = PTR_ERR(obj);
                        goto err_out;
                }
                ctx->legacy_hw_ctx.rcs_state = obj;
        }

        /* Default context will never have a file_priv */
        if (file_priv != NULL) {
                ret = idr_alloc(&file_priv->context_idr, ctx,
                                DEFAULT_CONTEXT_HANDLE, 0, GFP_KERNEL);
                if (ret < 0)
                        goto err_out;
        } else
                ret = DEFAULT_CONTEXT_HANDLE;

        ctx->file_priv = file_priv;
        ctx->user_handle = ret;
        /* NB: Mark all slices as needing a remap so that when the context first
         * loads it will restore whatever remap state already exists. If there
         * is no remap info, it will be a NOP. */
        ctx->remap_slice = (1 << NUM_L3_SLICES(dev)) - 1;

        return ctx;

err_out:
        i915_gem_context_unreference(ctx);
        return ERR_PTR(ret);
}

/**
 * The default context needs to exist per ring that uses contexts. It stores the
 * context state of the GPU for applications that don't utilize HW contexts, as
 * well as an idle case.
 */
static struct intel_context *
i915_gem_create_context(struct drm_device *dev,
                        struct drm_i915_file_private *file_priv)
{
        const bool is_global_default_ctx = file_priv == NULL;
        struct intel_context *ctx;
        int ret = 0;

        BUG_ON(!mutex_is_locked(&dev->struct_mutex));

        ctx = __create_hw_context(dev, file_priv);
        if (IS_ERR(ctx))
                return ctx;

        if (is_global_default_ctx && ctx->legacy_hw_ctx.rcs_state) {
                /* We may need to do things with the shrinker which
                 * require us to immediately switch back to the default
                 * context. This can cause a problem as pinning the
                 * default context also requires GTT space which may not
                 * be available. To avoid this we always pin the default
                 * context.
                 */
                ret = i915_gem_obj_ggtt_pin(ctx->legacy_hw_ctx.rcs_state,
                                            get_context_alignment(dev), 0);
                if (ret) {
                        DRM_DEBUG_DRIVER("Couldn't pin %d\n", ret);
                        goto err_destroy;
                }
        }

        if (USES_FULL_PPGTT(dev)) {
                struct i915_hw_ppgtt *ppgtt = i915_ppgtt_create(dev, file_priv);

                if (IS_ERR_OR_NULL(ppgtt)) {
                        DRM_DEBUG_DRIVER("PPGTT setup failed (%ld)\n",
                                         PTR_ERR(ppgtt));
                        ret = PTR_ERR(ppgtt);
                        goto err_unpin;
                }

                ctx->ppgtt = ppgtt;
        }

        return ctx;

err_unpin:
        if (is_global_default_ctx && ctx->legacy_hw_ctx.rcs_state)
                i915_gem_object_ggtt_unpin(ctx->legacy_hw_ctx.rcs_state);
err_destroy:
        i915_gem_context_unreference(ctx);
        return ERR_PTR(ret);
}

void i915_gem_context_reset(struct drm_device *dev)
{
        struct drm_i915_private *dev_priv = dev->dev_private;
        int i;

        /* In execlists mode we will unreference the context when the execlist
         * queue is cleared and the requests destroyed.
         */
        if (i915.enable_execlists)
                return;

        for (i = 0; i < I915_NUM_RINGS; i++) {
                struct intel_engine_cs *ring = &dev_priv->ring[i];
                struct intel_context *lctx = ring->last_context;

                if (lctx) {
                        if (lctx->legacy_hw_ctx.rcs_state && i == RCS)
                                i915_gem_object_ggtt_unpin(lctx->legacy_hw_ctx.rcs_state);

                        i915_gem_context_unreference(lctx);
                        ring->last_context = NULL;
                }
        }
}

int i915_gem_context_init(struct drm_device *dev)
{
        struct drm_i915_private *dev_priv = dev->dev_private;
        struct intel_context *ctx;
        int i;

        /* Init should only be called once per module load. Eventually the
         * restriction on the context_disabled check can be loosened. */
        if (WARN_ON(dev_priv->ring[RCS].default_context))
                return 0;

        if (i915.enable_execlists) {
                /* NB: intentionally left blank. We will allocate our own
                 * backing objects as we need them, thank you very much */
                dev_priv->hw_context_size = 0;
        } else if (HAS_HW_CONTEXTS(dev)) {
                dev_priv->hw_context_size = round_up(get_context_size(dev), 4096);
                if (dev_priv->hw_context_size > (1<<20)) {
                        DRM_DEBUG_DRIVER("Disabling HW Contexts; invalid size %d\n",
                                         dev_priv->hw_context_size);
                        dev_priv->hw_context_size = 0;
                }
        }

        ctx = i915_gem_create_context(dev, NULL);
        if (IS_ERR(ctx)) {
                DRM_ERROR("Failed to create default global context (error %ld)\n",
                          PTR_ERR(ctx));
                return PTR_ERR(ctx);
        }

        for (i = 0; i < I915_NUM_RINGS; i++) {
                struct intel_engine_cs *ring = &dev_priv->ring[i];

                /* NB: RCS will hold a ref for all rings */
                ring->default_context = ctx;
        }

        DRM_DEBUG_DRIVER("%s context support initialized\n",
                        i915.enable_execlists ? "LR" :
                        dev_priv->hw_context_size ? "HW" : "fake");
        return 0;
}

void i915_gem_context_fini(struct drm_device *dev)
{
        struct drm_i915_private *dev_priv = dev->dev_private;
        struct intel_context *dctx = dev_priv->ring[RCS].default_context;
        int i;

        if (dctx->legacy_hw_ctx.rcs_state) {
                /* The only known way to stop the gpu from accessing the hw context is
                 * to reset it. Do this as the very last operation to avoid confusing
                 * other code, leading to spurious errors. */
                intel_gpu_reset(dev);

                /* When default context is created and switched to, base object refcount
                 * will be 2 (+1 from object creation and +1 from do_switch()).
                 * i915_gem_context_fini() will be called after gpu_idle() has switched
                 * to default context. So we need to unreference the base object once
                 * to offset the do_switch part, so that i915_gem_context_unreference()
                 * can then free the base object correctly. */
                WARN_ON(!dev_priv->ring[RCS].last_context);
                if (dev_priv->ring[RCS].last_context == dctx) {
                        /* Fake switch to NULL context */
                        WARN_ON(dctx->legacy_hw_ctx.rcs_state->active);
                        i915_gem_object_ggtt_unpin(dctx->legacy_hw_ctx.rcs_state);
                        i915_gem_context_unreference(dctx);
                        dev_priv->ring[RCS].last_context = NULL;
                }

                i915_gem_object_ggtt_unpin(dctx->legacy_hw_ctx.rcs_state);
        }

        for (i = 0; i < I915_NUM_RINGS; i++) {
                struct intel_engine_cs *ring = &dev_priv->ring[i];

                if (ring->last_context)
                        i915_gem_context_unreference(ring->last_context);

                ring->default_context = NULL;
                ring->last_context = NULL;
        }

        i915_gem_context_unreference(dctx);
}

int i915_gem_context_enable(struct drm_i915_private *dev_priv)
{
        struct intel_engine_cs *ring;
        int ret, i;

        BUG_ON(!dev_priv->ring[RCS].default_context);

        if (i915.enable_execlists)
                return 0;

        for_each_ring(ring, dev_priv, i) {
                ret = i915_switch_context(ring, ring->default_context);
                if (ret)
                        return ret;
        }

        return 0;
}

static int context_idr_cleanup(int id, void *p, void *data)
{
        struct intel_context *ctx = p;

        i915_gem_context_unreference(ctx);
        return 0;
}

int i915_gem_context_open(struct drm_device *dev, struct drm_file *file)
{
        struct drm_i915_file_private *file_priv = file->driver_priv;
        struct intel_context *ctx;

        idr_init(&file_priv->context_idr);

        mutex_lock(&dev->struct_mutex);
        ctx = i915_gem_create_context(dev, file_priv);
        mutex_unlock(&dev->struct_mutex);

        if (IS_ERR(ctx)) {
                idr_destroy(&file_priv->context_idr);
                return PTR_ERR(ctx);
        }

        return 0;
}

void i915_gem_context_close(struct drm_device *dev, struct drm_file *file)
{
        struct drm_i915_file_private *file_priv = file->driver_priv;

        idr_for_each(&file_priv->context_idr, context_idr_cleanup, NULL);
        idr_destroy(&file_priv->context_idr);
}

struct intel_context *
i915_gem_context_get(struct drm_i915_file_private *file_priv, u32 id)
{
        struct intel_context *ctx;

        ctx = (struct intel_context *)idr_find(&file_priv->context_idr, id);
        if (!ctx)
                return ERR_PTR(-ENOENT);

        return ctx;
}

static inline int
mi_set_context(struct intel_engine_cs *ring,
               struct intel_context *new_context,
               u32 hw_flags)
{
        u32 flags = hw_flags | MI_MM_SPACE_GTT;
        const int num_rings =
                /* Use an extended w/a on ivb+ if signalling from other rings */
                i915_semaphore_is_enabled(ring->dev) ?
                hweight32(INTEL_INFO(ring->dev)->ring_mask) - 1 :
                0;
        int len, i, ret;

        /* w/a: If Flush TLB Invalidation Mode is enabled, driver must do a TLB
         * invalidation prior to MI_SET_CONTEXT. On GEN6 we don't set the value
         * explicitly, so we rely on the value at ring init, stored in
         * itlb_before_ctx_switch.
         */
        if (IS_GEN6(ring->dev)) {
                ret = ring->flush(ring, I915_GEM_GPU_DOMAINS, 0);
                if (ret)
                        return ret;
        }

        /* These flags are for resource streamer on HSW+ */
        if (!IS_HASWELL(ring->dev) && INTEL_INFO(ring->dev)->gen < 8)
                flags |= (MI_SAVE_EXT_STATE_EN | MI_RESTORE_EXT_STATE_EN);

        len = 4;
        if (INTEL_INFO(ring->dev)->gen >= 7)
                len += 2 + (num_rings ? 4*num_rings + 2 : 0);

        ret = intel_ring_begin(ring, len);
        if (ret)
                return ret;

        /* WaProgramMiArbOnOffAroundMiSetContext:ivb,vlv,hsw,bdw,chv */
        if (INTEL_INFO(ring->dev)->gen >= 7) {
                intel_ring_emit(ring, MI_ARB_ON_OFF | MI_ARB_DISABLE);
                if (num_rings) {
                        struct intel_engine_cs *signaller;

                        intel_ring_emit(ring, MI_LOAD_REGISTER_IMM(num_rings));
                        for_each_ring(signaller, to_i915(ring->dev), i) {
                                if (signaller == ring)
                                        continue;

                                intel_ring_emit(ring, RING_PSMI_CTL(signaller->mmio_base));
                                intel_ring_emit(ring, _MASKED_BIT_ENABLE(GEN6_PSMI_SLEEP_MSG_DISABLE));
                        }
                }
        }

        intel_ring_emit(ring, MI_NOOP);
        intel_ring_emit(ring, MI_SET_CONTEXT);
        intel_ring_emit(ring, i915_gem_obj_ggtt_offset(new_context->legacy_hw_ctx.rcs_state) |
                        flags);
        /*
         * w/a: MI_SET_CONTEXT must always be followed by MI_NOOP
         * WaMiSetContext_Hang:snb,ivb,vlv
         */
        intel_ring_emit(ring, MI_NOOP);

        if (INTEL_INFO(ring->dev)->gen >= 7) {
                if (num_rings) {
                        struct intel_engine_cs *signaller;

                        intel_ring_emit(ring, MI_LOAD_REGISTER_IMM(num_rings));
                        for_each_ring(signaller, to_i915(ring->dev), i) {
                                if (signaller == ring)
                                        continue;

                                intel_ring_emit(ring, RING_PSMI_CTL(signaller->mmio_base));
                                intel_ring_emit(ring, _MASKED_BIT_DISABLE(GEN6_PSMI_SLEEP_MSG_DISABLE));
                        }
                }
                intel_ring_emit(ring, MI_ARB_ON_OFF | MI_ARB_ENABLE);
        }

        intel_ring_advance(ring);

        return ret;
}

static int do_switch(struct intel_engine_cs *ring,
                     struct intel_context *to)
{
        struct drm_i915_private *dev_priv = ring->dev->dev_private;
        struct intel_context *from = ring->last_context;
        u32 hw_flags = 0;
        bool uninitialized = false;
        int ret, i;

        if (from != NULL && ring == &dev_priv->ring[RCS]) {
                BUG_ON(from->legacy_hw_ctx.rcs_state == NULL);
                BUG_ON(!i915_gem_obj_is_pinned(from->legacy_hw_ctx.rcs_state));
        }

        if (from == to && !to->remap_slice)
                return 0;

        /* Trying to pin first makes error handling easier. */
        if (ring == &dev_priv->ring[RCS]) {
                ret = i915_gem_obj_ggtt_pin(to->legacy_hw_ctx.rcs_state,
                                            get_context_alignment(ring->dev), 0);
                if (ret)
                        return ret;
        }

        /*
         * Pin can switch back to the default context if we end up calling into
         * evict_everything - as a last ditch gtt defrag effort that also
         * switches to the default context. Hence we need to reload from here.
         */
        from = ring->last_context;

        if (to->ppgtt) {
                ret = to->ppgtt->switch_mm(to->ppgtt, ring);
                if (ret)
                        goto unpin_out;
        }

        if (ring != &dev_priv->ring[RCS]) {
                if (from)
                        i915_gem_context_unreference(from);
                goto done;
        }

        /*
         * Clear this page out of any CPU caches for coherent swap-in/out. Note
         * that thanks to write = false in this call and us not setting any gpu
         * write domains when putting a context object onto the active list
         * (when switching away from it), this won't block.
         *
         * XXX: We need a real interface to do this instead of trickery.
         */
        ret = i915_gem_object_set_to_gtt_domain(to->legacy_hw_ctx.rcs_state, false);
        if (ret)
                goto unpin_out;

        if (!to->legacy_hw_ctx.rcs_state->has_global_gtt_mapping) {
                struct i915_vma *vma = i915_gem_obj_to_vma(to->legacy_hw_ctx.rcs_state,
                                                           &dev_priv->gtt.base);
                vma->bind_vma(vma, to->legacy_hw_ctx.rcs_state->cache_level, GLOBAL_BIND);
        }

        if (!to->legacy_hw_ctx.initialized || i915_gem_context_is_default(to))
                hw_flags |= MI_RESTORE_INHIBIT;

        ret = mi_set_context(ring, to, hw_flags);
        if (ret)
                goto unpin_out;

        for (i = 0; i < MAX_L3_SLICES; i++) {
                if (!(to->remap_slice & (1<<i)))
                        continue;

                ret = i915_gem_l3_remap(ring, i);
                /* If it failed, try again next round */
                if (ret)
                        DRM_DEBUG_DRIVER("L3 remapping failed\n");
                else
                        to->remap_slice &= ~(1<<i);
        }

        /* The backing object for the context is done after switching to the
         * *next* context. Therefore we cannot retire the previous context until
         * the next context has already started running. In fact, the below code
         * is a bit suboptimal because the retiring can occur simply after the
         * MI_SET_CONTEXT instead of when the next seqno has completed.
         */
        if (from != NULL) {
                from->legacy_hw_ctx.rcs_state->base.read_domains = I915_GEM_DOMAIN_INSTRUCTION;
                i915_vma_move_to_active(i915_gem_obj_to_ggtt(from->legacy_hw_ctx.rcs_state), ring);
                /* As long as MI_SET_CONTEXT is serializing, ie. it flushes the
                 * whole damn pipeline, we don't need to explicitly mark the
                 * object dirty. The only exception is that the context must be
                 * correct in case the object gets swapped out. Ideally we'd be
                 * able to defer doing this until we know the object would be
                 * swapped, but there is no way to do that yet.
                 */
                from->legacy_hw_ctx.rcs_state->dirty = 1;
                BUG_ON(from->legacy_hw_ctx.rcs_state->ring != ring);

                /* obj is kept alive until the next request by its active ref */
                i915_gem_object_ggtt_unpin(from->legacy_hw_ctx.rcs_state);
                i915_gem_context_unreference(from);
        }

        uninitialized = !to->legacy_hw_ctx.initialized && from == NULL;
        to->legacy_hw_ctx.initialized = true;

done:
        i915_gem_context_reference(to);
        ring->last_context = to;

        if (uninitialized) {
                if (ring->init_context) {
                        ret = ring->init_context(ring);
                        if (ret)
                                DRM_ERROR("ring init context: %d\n", ret);
                }

                ret = i915_gem_render_state_init(ring);
                if (ret)
                        DRM_ERROR("init render state: %d\n", ret);
        }

        return 0;

unpin_out:
        if (ring->id == RCS)
                i915_gem_object_ggtt_unpin(to->legacy_hw_ctx.rcs_state);
        return ret;
}

/**
 * i915_switch_context() - perform a GPU context switch.
 * @ring: ring for which we'll execute the context switch
 * @to: the context to switch to
 *
 * The context life cycle is simple. The context refcount is incremented and
 * decremented by 1 and create and destroy. If the context is in use by the GPU,
 * it will have a refcount > 1. This allows us to destroy the context abstract
 * object while letting the normal object tracking destroy the backing BO.
 *
 * This function should not be used in execlists mode.  Instead the context is
 * switched by writing to the ELSP and requests keep a reference to their
 * context.
 */
int i915_switch_context(struct intel_engine_cs *ring,
                        struct intel_context *to)
{
        struct drm_i915_private *dev_priv = ring->dev->dev_private;

        WARN_ON(i915.enable_execlists);
        WARN_ON(!mutex_is_locked(&dev_priv->dev->struct_mutex));

        if (to->legacy_hw_ctx.rcs_state == NULL) { /* We have the fake context */
                if (to != ring->last_context) {
                        i915_gem_context_reference(to);
                        if (ring->last_context)
                                i915_gem_context_unreference(ring->last_context);
                        ring->last_context = to;
                }
                return 0;
        }

        return do_switch(ring, to);
}

static bool contexts_enabled(struct drm_device *dev)
{
        return i915.enable_execlists || to_i915(dev)->hw_context_size;
}

int i915_gem_context_create_ioctl(struct drm_device *dev, void *data,
                                  struct drm_file *file)
{
        struct drm_i915_gem_context_create *args = data;
        struct drm_i915_file_private *file_priv = file->driver_priv;
        struct intel_context *ctx;
        int ret;

        if (!contexts_enabled(dev))
                return -ENODEV;

        ret = i915_mutex_lock_interruptible(dev);
        if (ret)
                return ret;

        ctx = i915_gem_create_context(dev, file_priv);
        mutex_unlock(&dev->struct_mutex);
        if (IS_ERR(ctx))
                return PTR_ERR(ctx);

        args->ctx_id = ctx->user_handle;
        DRM_DEBUG_DRIVER("HW context %d created\n", args->ctx_id);

        return 0;
}

int i915_gem_context_destroy_ioctl(struct drm_device *dev, void *data,
                                   struct drm_file *file)
{
        struct drm_i915_gem_context_destroy *args = data;
        struct drm_i915_file_private *file_priv = file->driver_priv;
        struct intel_context *ctx;
        int ret;

        if (args->ctx_id == DEFAULT_CONTEXT_HANDLE)
                return -ENOENT;

        ret = i915_mutex_lock_interruptible(dev);
        if (ret)
                return ret;

        ctx = i915_gem_context_get(file_priv, args->ctx_id);
        if (IS_ERR(ctx)) {
                mutex_unlock(&dev->struct_mutex);
                return PTR_ERR(ctx);
        }

        idr_remove(&ctx->file_priv->context_idr, ctx->user_handle);
        i915_gem_context_unreference(ctx);
        mutex_unlock(&dev->struct_mutex);

        DRM_DEBUG_DRIVER("HW context %d destroyed\n", args->ctx_id);
        return 0;
}