// SPDX-License-Identifier: MIT
/*
 * Copyright © 2014-2016 Intel Corporation
 */

#include <linux/dma-fence-array.h>

#include "gt/intel_engine.h"

#include "i915_gem_ioctls.h"
#include "i915_gem_object.h"

static __always_inline u32 __busy_read_flag(u16 id)
{
        if (id == (u16)I915_ENGINE_CLASS_INVALID)
                return 0xffff0000u;

        GEM_BUG_ON(id >= 16);
        return 0x10000u << id;
}

static __always_inline u32 __busy_write_id(u16 id)
{
        /*
         * The uABI guarantees an active writer is also amongst the read
         * engines. This would be true if we accessed the activity tracking
         * under the lock, but as we perform the lookup of the object and
         * its activity locklessly we can not guarantee that the last_write
         * being active implies that we have set the same engine flag from
         * last_read - hence we always set both read and write busy for
         * last_write.
         */
        if (id == (u16)I915_ENGINE_CLASS_INVALID)
                return 0xffffffffu;

        return (id + 1) | __busy_read_flag(id);
}

static __always_inline unsigned int
__busy_set_if_active(struct dma_fence *fence, u32 (*flag)(u16 id))
{
        const struct i915_request *rq;

        /*
         * We have to check the current hw status of the fence as the uABI
         * guarantees forward progress. We could rely on the idle worker
         * to eventually flush us, but to minimise latency just ask the
         * hardware.
         *
         * Note we only report on the status of native fences and we currently
         * have two native fences:
         *
         * 1. A composite fence (dma_fence_array) constructed of i915 requests
         * created during a parallel submission. In this case we deconstruct the
         * composite fence into individual i915 requests and check the status of
         * each request.
         *
         * 2. A single i915 request.
         */
        if (dma_fence_is_array(fence)) {
                struct dma_fence_array *array = to_dma_fence_array(fence);
                struct dma_fence **child = array->fences;
                unsigned int nchild = array->num_fences;

                do {
                        struct dma_fence *current_fence = *child++;

                        /* Not an i915 fence, can't be busy per above */
                        if (!dma_fence_is_i915(current_fence) ||
                            !test_bit(I915_FENCE_FLAG_COMPOSITE,
                                      &current_fence->flags)) {
                                return 0;
                        }

                        rq = to_request(current_fence);
                        if (!i915_request_completed(rq))
                                return flag(rq->engine->uabi_class);
                } while (--nchild);

                /* All requests in array complete, not busy */
                return 0;
        } else {
                if (!dma_fence_is_i915(fence))
                        return 0;

                rq = to_request(fence);
                if (i915_request_completed(rq))
                        return 0;

                /* Beware type-expansion follies! */
                BUILD_BUG_ON(!typecheck(u16, rq->engine->uabi_class));
                return flag(rq->engine->uabi_class);
        }
}

static __always_inline unsigned int
busy_check_reader(struct dma_fence *fence)
{
        return __busy_set_if_active(fence, __busy_read_flag);
}

static __always_inline unsigned int
busy_check_writer(struct dma_fence *fence)
{
        if (!fence)
                return 0;

        return __busy_set_if_active(fence, __busy_write_id);
}

int
i915_gem_busy_ioctl(struct drm_device *dev, void *data,
                    struct drm_file *file)
{
        struct drm_i915_gem_busy *args = data;
        struct drm_i915_gem_object *obj;
        struct dma_resv_iter cursor;
        struct dma_fence *fence;
        int err;

        err = -ENOENT;
        rcu_read_lock();
        obj = i915_gem_object_lookup_rcu(file, args->handle);
        if (!obj)
                goto out;

        /*
         * A discrepancy here is that we do not report the status of
         * non-i915 fences, i.e. even though we may report the object as idle,
         * a call to set-domain may still stall waiting for foreign rendering.
         * This also means that wait-ioctl may report an object as busy,
         * where busy-ioctl considers it idle.
         *
         * We trade the ability to warn of foreign fences to report on which
         * i915 engines are active for the object.
         *
         * Alternatively, we can trade that extra information on read/write
         * activity with
         *      args->busy =
         *              !dma_resv_test_signaled(obj->resv, DMA_RESV_USAGE_READ);
         * to report the overall busyness. This is what the wait-ioctl does.
         *
         */
        args->busy = 0;
        dma_resv_iter_begin(&cursor, obj->base.resv, DMA_RESV_USAGE_READ);
        dma_resv_for_each_fence_unlocked(&cursor, fence) {
                if (dma_resv_iter_is_restarted(&cursor))
                        args->busy = 0;

                if (dma_resv_iter_usage(&cursor) <= DMA_RESV_USAGE_WRITE)
                        /* Translate the write fences to the READ *and* WRITE engine */
                        args->busy |= busy_check_writer(fence);
                else
                        /* Translate read fences to READ set of engines */
                        args->busy |= busy_check_reader(fence);
        }
        dma_resv_iter_end(&cursor);

        err = 0;
out:
        rcu_read_unlock();
        return err;
}