i915_gem_context.c

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/*
 * 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 <[email protected]>
 *
 */

/*
 * 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 it's 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 CONTEXT_ALIGN (64<<10)

static struct i915_hw_context *
i915_gem_context_get(struct drm_i915_file_private *file_priv, u32 id);
static int do_switch(struct i915_hw_context *to);

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(reg) * 64;
        else
            ret = GEN7_CXT_TOTAL_SIZE(reg) * 64;
        break;
    default:
        BUG();
    }

    return ret;
}

static void do_destroy(struct i915_hw_context *ctx)
{
    struct drm_device *dev = ctx->obj->base.dev;
    struct drm_i915_private *dev_priv = dev->dev_private;

    if (ctx->file_priv)
        idr_remove(&ctx->file_priv->context_idr, ctx->id);
    else
        BUG_ON(ctx != dev_priv->ring[RCS].default_context);

    drm_gem_object_unreference(&ctx->obj->base);
    kfree(ctx);
}

static struct i915_hw_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 i915_hw_context *ctx;
    int ret, id;

    ctx = kzalloc(sizeof(struct drm_i915_file_private), GFP_KERNEL);
    if (ctx == NULL)
        return ERR_PTR(-ENOMEM);

    ctx->obj = i915_gem_alloc_object(dev, dev_priv->hw_context_size);
    if (ctx->obj == NULL) {
        kfree(ctx);
        DRM_DEBUG_DRIVER("Context object allocated failed\n");
        return ERR_PTR(-ENOMEM);
    }

    /* The ring associated with the context object is handled by the normal
     * object tracking code. We give an initial ring value simple to pass an
     * assertion in the context switch code.
     */
    ctx->ring = &dev_priv->ring[RCS];

    /* Default context will never have a file_priv */
    if (file_priv == NULL)
        return ctx;

    ctx->file_priv = file_priv;

again:
    if (idr_pre_get(&file_priv->context_idr, GFP_KERNEL) == 0) {
        ret = -ENOMEM;
        DRM_DEBUG_DRIVER("idr allocation failed\n");
        goto err_out;
    }

    ret = idr_get_new_above(&file_priv->context_idr, ctx,
                DEFAULT_CONTEXT_ID + 1, &id);
    if (ret == 0)
        ctx->id = id;

    if (ret == -EAGAIN)
        goto again;
    else if (ret)
        goto err_out;

    return ctx;

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

static inline bool is_default_context(struct i915_hw_context *ctx)
{
    return (ctx == ctx->ring->default_context);
}

static int create_default_context(struct drm_i915_private *dev_priv)
{
    struct i915_hw_context *ctx;
    int ret;

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

    ctx = create_hw_context(dev_priv->dev, NULL);
    if (IS_ERR(ctx))
        return PTR_ERR(ctx);

    /* 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.
     */
    dev_priv->ring[RCS].default_context = ctx;
    ret = i915_gem_object_pin(ctx->obj, CONTEXT_ALIGN, false, false);
    if (ret)
        goto err_destroy;

    ret = do_switch(ctx);
    if (ret)
        goto err_unpin;

    DRM_DEBUG_DRIVER("Default HW context loaded\n");
    return 0;

err_unpin:
    i915_gem_object_unpin(ctx->obj);
err_destroy:
    do_destroy(ctx);
    return ret;
}

void i915_gem_context_init(struct drm_device *dev)
{
    struct drm_i915_private *dev_priv = dev->dev_private;
    uint32_t ctx_size;

    if (!HAS_HW_CONTEXTS(dev)) {
        dev_priv->hw_contexts_disabled = true;
        return;
    }

    /* If called from reset, or thaw... we've been here already */
    if (dev_priv->hw_contexts_disabled ||
        dev_priv->ring[RCS].default_context)
        return;

    ctx_size = get_context_size(dev);
    dev_priv->hw_context_size = get_context_size(dev);
    dev_priv->hw_context_size = round_up(dev_priv->hw_context_size, 4096);

    if (ctx_size <= 0 || ctx_size > (1<<20)) {
        dev_priv->hw_contexts_disabled = true;
        return;
    }

    if (create_default_context(dev_priv)) {
        dev_priv->hw_contexts_disabled = true;
        return;
    }

    DRM_DEBUG_DRIVER("HW context support initialized\n");
}

void i915_gem_context_fini(struct drm_device *dev)
{
    struct drm_i915_private *dev_priv = dev->dev_private;

    if (dev_priv->hw_contexts_disabled)
        return;

    /* 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);

    i915_gem_object_unpin(dev_priv->ring[RCS].default_context->obj);

    do_destroy(dev_priv->ring[RCS].default_context);
}

static int context_idr_cleanup(int id, void *p, void *data)
{
    struct i915_hw_context *ctx = p;

    BUG_ON(id == DEFAULT_CONTEXT_ID);

    do_destroy(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;

    mutex_lock(&dev->struct_mutex);
    idr_for_each(&file_priv->context_idr, context_idr_cleanup, NULL);
    idr_destroy(&file_priv->context_idr);
    mutex_unlock(&dev->struct_mutex);
}

static struct i915_hw_context *
i915_gem_context_get(struct drm_i915_file_private *file_priv, u32 id)
{
    return (struct i915_hw_context *)idr_find(&file_priv->context_idr, id);
}

static inline int
mi_set_context(struct intel_ring_buffer *ring,
           struct i915_hw_context *new_context,
           u32 hw_flags)
{
    int 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) && ring->itlb_before_ctx_switch) {
        ret = ring->flush(ring, I915_GEM_GPU_DOMAINS, 0);
        if (ret)
            return ret;
    }

    ret = intel_ring_begin(ring, 6);
    if (ret)
        return ret;

    if (IS_GEN7(ring->dev))
        intel_ring_emit(ring, MI_ARB_ON_OFF | MI_ARB_DISABLE);
    else
        intel_ring_emit(ring, MI_NOOP);

    intel_ring_emit(ring, MI_NOOP);
    intel_ring_emit(ring, MI_SET_CONTEXT);
    intel_ring_emit(ring, new_context->obj->gtt_offset |
            MI_MM_SPACE_GTT |
            MI_SAVE_EXT_STATE_EN |
            MI_RESTORE_EXT_STATE_EN |
            hw_flags);
    /* w/a: MI_SET_CONTEXT must always be followed by MI_NOOP */
    intel_ring_emit(ring, MI_NOOP);

    if (IS_GEN7(ring->dev))
        intel_ring_emit(ring, MI_ARB_ON_OFF | MI_ARB_ENABLE);
    else
        intel_ring_emit(ring, MI_NOOP);

    intel_ring_advance(ring);

    return ret;
}

static int do_switch(struct i915_hw_context *to)
{
    struct intel_ring_buffer *ring = to->ring;
    struct drm_i915_gem_object *from_obj = ring->last_context_obj;
    u32 hw_flags = 0;
    int ret;

    BUG_ON(from_obj != NULL && from_obj->pin_count == 0);

    if (from_obj == to->obj)
        return 0;

    ret = i915_gem_object_pin(to->obj, CONTEXT_ALIGN, false, false);
    if (ret)
        return ret;

    /* 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->obj, false);
    if (ret) {
        i915_gem_object_unpin(to->obj);
        return ret;
    }

    if (!to->obj->has_global_gtt_mapping)
        i915_gem_gtt_bind_object(to->obj, to->obj->cache_level);

    if (!to->is_initialized || is_default_context(to))
        hw_flags |= MI_RESTORE_INHIBIT;
    else if (WARN_ON_ONCE(from_obj == to->obj)) /* not yet expected */
        hw_flags |= MI_FORCE_RESTORE;

    ret = mi_set_context(ring, to, hw_flags);
    if (ret) {
        i915_gem_object_unpin(to->obj);
        return ret;
    }

    /* 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_obj != NULL) {
        u32 seqno = i915_gem_next_request_seqno(ring);
        from_obj->base.read_domains = I915_GEM_DOMAIN_INSTRUCTION;
        i915_gem_object_move_to_active(from_obj, ring, seqno);
        /* 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_obj->dirty = 1;
        BUG_ON(from_obj->ring != ring);
        i915_gem_object_unpin(from_obj);

        drm_gem_object_unreference(&from_obj->base);
    }

    drm_gem_object_reference(&to->obj->base);
    ring->last_context_obj = to->obj;
    to->is_initialized = true;

    return 0;
}

int i915_switch_context(struct intel_ring_buffer *ring,
            struct drm_file *file,
            int to_id)
{
    struct drm_i915_private *dev_priv = ring->dev->dev_private;
    struct i915_hw_context *to;

    if (dev_priv->hw_contexts_disabled)
        return 0;

    if (ring != &dev_priv->ring[RCS])
        return 0;

    if (to_id == DEFAULT_CONTEXT_ID) {
        to = ring->default_context;
    } else {
        if (file == NULL)
            return -EINVAL;

        to = i915_gem_context_get(file->driver_priv, to_id);
        if (to == NULL)
            return -ENOENT;
    }

    return do_switch(to);
}

int i915_gem_context_create_ioctl(struct drm_device *dev, void *data,
                  struct drm_file *file)
{
    struct drm_i915_private *dev_priv = dev->dev_private;
    struct drm_i915_gem_context_create *args = data;
    struct drm_i915_file_private *file_priv = file->driver_priv;
    struct i915_hw_context *ctx;
    int ret;

    if (!(dev->driver->driver_features & DRIVER_GEM))
        return -ENODEV;

    if (dev_priv->hw_contexts_disabled)
        return -ENODEV;

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

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

    args->ctx_id = ctx->id;
    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 i915_hw_context *ctx;
    int ret;

    if (!(dev->driver->driver_features & DRIVER_GEM))
        return -ENODEV;

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

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

    do_destroy(ctx);

    mutex_unlock(&dev->struct_mutex);

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