/**
 * MVGAL - Multi-Vendor GPU Aggregation Layer for Linux
 * 
 * AMD GPU Driver Integration (amdgpu)
 * 
 * SPDX-License-Identifier: GPL-2.0-only
 *
 * Study references:
 * - drivers/gpu/drm/amd/ in upstream Linux kernel
 * - AMDVLK Vulkan ICD (historical)
 * - RADV Vulkan driver in Mesa
 * - ROCK Kernel Driver: https://github.com/GPUOpen-Drivers/ROCK-Kernel-Driver
 */

#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/pci.h>
#include <linux/slab.h>
#include <linux/dma-buf.h>
#include <linux/spinlock.h>

#include "../mvgal_core.h"
#include "../mvgal_device.h"
#include "../mvgal_scheduler.h"
#include "mvgal_amd.h"

/* AMD vendor operations */
const struct mvgal_vendor_ops mvgal_amd_ops = {
	.init = mvgal_amd_init,
	.fini = mvgal_amd_fini,
	.submit_cs = mvgal_amd_submit_cs,
	.alloc_vram = mvgal_amd_alloc_vram,
	.free_vram = mvgal_amd_free_vram,
	.wait_idle = mvgal_amd_wait_idle,
	.set_power_state = mvgal_amd_set_power_state,
	.export_dmabuf = mvgal_amd_export_dmabuf,
	.import_dmabuf = mvgal_amd_import_dmabuf,
	.query_utilization = mvgal_amd_query_utilization,
};

/*
 * Per-GPU AMD private data
 */
struct mvgal_amd_alloc {
    struct list_head node;
    uint64_t id;
    size_t size;
    uint64_t gpu_addr;
    void *bo;  /* TTM buffer object pointer */
};

struct mvgal_amd_priv {
	struct pci_dev *pdev;
	struct drm_device *drm_dev;       /* Pointer to amdgpu DRM device */
	
	/* TTM buffer object for allocations */
	struct {
		bool ttm_available;
		struct list_head alloc_list;  /* Track allocations */
	} ttm;
	
	/* Capabilities */
	uint64_t vram_total;
	uint64_t vram_vis_total;
	uint64_t gtt_total;
	uint32_t num_rings;              /* Number of command rings */
	
	/* DMA-BUF support */
	bool can_export_dmabuf;
	bool can_import_dmabuf;
	
	/* Power management */
	bool dpm_supported;              /* Dynamic Power Management supported */
	char power_profile[32];         /* Current power profile */
};

/* Simple VRAM allocator - allocates from a reserved range */
static uint64_t amd_vram_current_addr = 0x100000000ULL;  /* 4GB start */
static DEFINE_SPINLOCK(amd_vram_lock);

/**
 * mvgal_amd_init - Initialize AMD GPU
 */
int mvgal_amd_init(struct mvgal_gpu_device *gpu)
{
	struct mvgal_amd_priv *priv;
	struct drm_device *ddev = NULL;

	if (!gpu) {
		return -EINVAL;
	}

	priv = kzalloc(sizeof(*priv), GFP_KERNEL);
	if (!priv) {
		return -ENOMEM;
	}

	priv->pdev = gpu->pdev;
	
	/* Attempt to get the drm_device from PCI drvdata */
	ddev = pci_get_drvdata(gpu->pdev);
	if (ddev) {
		priv->drm_dev = ddev;
		pr_debug("MVGAL: Found AMD DRM device %p for PCI %s\n", ddev, pci_name(gpu->pdev));
	}

	/* Check for TTM support */
	priv->ttm.ttm_available = true; /* amdgpu uses TTM */
	INIT_LIST_HEAD(&priv->ttm.alloc_list);

	/* Check for DMA-BUF support */
	priv->can_export_dmabuf = true; /* amdgpu supports DMA-BUF export */
	priv->can_import_dmabuf = true; /* amdgpu supports DMA-BUF import */

	/* Check for DPM */
	priv->dpm_supported = true; /* Most modern AMD GPUs support DPM */

	/* Set reasonable defaults for AMD GPUs */
	gpu->vram_size = pci_resource_len(gpu->pdev, 0); /* BAR0 is VRAM on AMD */
	gpu->vram_bandwidth = 512 * 1024; /* ~512 GB/s */
	gpu->compute_units = 72; /* 72 CUs for RDNA 2 */
	gpu->api_flags = MVGAL_API_VULKAN | MVGAL_API_OPENCL;

	/* Set private data */
	gpu->vendor_priv = priv;

	pr_info("MVGAL: AMD GPU initialized (pci %04x:%04x, vram %llu MB)\n",
		gpu->pci_vendor_id, gpu->pci_device_id, (unsigned long long)(gpu->vram_size >> 20));

	return 0;
}

/**
 * mvgal_amd_fini - Cleanup AMD GPU
 */
void mvgal_amd_fini(struct mvgal_gpu_device *gpu)
{
	struct mvgal_amd_priv *priv = gpu->vendor_priv;
	struct mvgal_amd_alloc *alloc, *tmp;

	if (!priv) {
		return;
	}

	/* Free any tracked allocations */
	list_for_each_entry_safe(alloc, tmp, &priv->ttm.alloc_list, node) {
		list_del(&alloc->node);
		kfree(alloc);
	}

	kfree(priv);
	gpu->vendor_priv = NULL;

	pr_info("MVGAL: AMD GPU finalized\n");
}

/**
 * mvgal_amd_submit_cs - Submit command stream to AMD GPU
 * 
 * Uses amdgpu's ring scheduling system.
 */
int mvgal_amd_submit_cs(struct mvgal_gpu_device *gpu, struct mvgal_workload *workload)
{
	struct mvgal_amd_priv *priv = gpu->vendor_priv;

	if (!priv || !workload) {
		return -EINVAL;
	}

	/* In the full implementation:
	 * 1. Get the amdgpu_device from priv->drm_dev->dev_private
	 * 2. Access amdgpu_ring structures via amalgamator_gpu->rings
	 * 3. Use amdgpu_job_alloc(), amdgpu_job_add_bo(), amdgpu_job_submit()
	 * 
	 * Study references:
	 * - drivers/gpu/drm/amd/scheduler/amdgpu_sched.c
	 * - drivers/gpu/drm/amd/amdgpu_job.c
	 * - drivers/gpu/drm/amd/amdgpu_ring.c
	 */

	pr_debug("MVGAL: AMD submit_cs (workload %d, size %zu)\n",
		workload->id, workload->command_buffer_size);

	/* For now, mark as submitted */
	return 0;
}

/**
 * mvgal_amd_alloc_vram - Allocate VRAM on AMD GPU
 * 
 * Uses TTM buffer object allocation.
 */
int mvgal_amd_alloc_vram(struct mvgal_gpu_device *gpu, size_t size, uint64_t *gpu_addr)
{
	struct mvgal_amd_priv *priv = gpu->vendor_priv;
	struct mvgal_amd_alloc *alloc;
	unsigned long flags;
	uint64_t addr;

	if (!priv || !gpu_addr) {
		return -EINVAL;
	}

	/* Align size to page boundary */
	size = ALIGN(size, PAGE_SIZE);
	if (size == 0) {
		return -EINVAL;
	}

	/* Simple bump allocator - reserves addresses in controlled range */
	spin_lock_irqsave(&amd_vram_lock, flags);
	addr = amd_vram_current_addr;
	
	/* Check for overflow */
	if (addr + size > gpu->vram_size + 0x100000000ULL) {
		spin_unlock_irqrestore(&amd_vram_lock, flags);
		return -ENOMEM;
	}
	amd_vram_current_addr += size;
	spin_unlock_irqrestore(&amd_vram_lock, flags);

	/* Track the allocation */
	alloc = kmalloc(sizeof(*alloc), GFP_KERNEL);
	if (!alloc) {
		return -ENOMEM;
	}
	alloc->size = size;
	alloc->gpu_addr = addr;
	alloc->bo = NULL;  /* No TTM BO in this mode - placeholder for real implementation */
	INIT_LIST_HEAD(&alloc->node);
	list_add(&alloc->node, &priv->ttm.alloc_list);

	*gpu_addr = addr;
	
	pr_debug("MVGAL: AMD alloc_vram (size %zu, addr %016llx)\n", size, *gpu_addr);

	return 0;
}

/**
 * mvgal_amd_free_vram - Free VRAM on AMD GPU
 */
void mvgal_amd_free_vram(struct mvgal_gpu_device *gpu, uint64_t gpu_addr)
{
	struct mvgal_amd_priv *priv = gpu->vendor_priv;
	struct mvgal_amd_alloc *alloc, *tmp;

	if (!priv) {
		return;
	}

	/* Find and remove the allocation */
	list_for_each_entry_safe(alloc, tmp, &priv->ttm.alloc_list, node) {
		if (alloc->gpu_addr == gpu_addr) {
			list_del(&alloc->node);
			kfree(alloc);
			pr_debug("MVGAL: AMD free_vram (addr %016llx) - tracked\n", gpu_addr);
			return;
		}
	}

	/* In the full implementation:
	 * 1. Find the TTM BO for this address
	 * 2. Call ttm_bo_put() to release reference
	 */

	pr_debug("MVGAL: AMD free_vram (addr %016llx)\n", gpu_addr);
}

/**
 * mvgal_amd_wait_idle - Wait for AMD GPU to be idle
 */
int mvgal_amd_wait_idle(struct mvgal_gpu_device *gpu, uint32_t timeout_ms)
{
	struct mvgal_amd_priv *priv = gpu->vendor_priv;

	if (!priv) {
		return -EINVAL;
	}

	/* In the full implementation:
	 * 1. Check amdgpu_device->job_scheduling (is busy)
	 * 2. Or wait for all rings to be idle
	 * 3. Use amdgpu_device_wait_idle() if available
	 */

	pr_debug("MVGAL: AMD wait_idle (timeout %ums)\n", timeout_ms);

	return 0;
}

/**
 * mvgal_amd_set_power_state - Set AMD GPU power state via sysfs DPM
 *
 * Writes to power_dpm_force_performance_level which is the standard
 * amdgpu interface for forcing a power/performance level.
 *
 * Values:
 *   "auto"   — driver manages clocks automatically (MVGAL_POWER_STATE_ACTIVE)
 *   "low"    — force lowest P-state (MVGAL_POWER_STATE_IDLE / PARK)
 *   "high"   — force highest P-state (MVGAL_POWER_STATE_SUSTAINED)
 *   "manual" — manual clock control (not used here)
 */
int mvgal_amd_set_power_state(struct mvgal_gpu_device *gpu, enum mvgal_power_state state)
{
	struct mvgal_amd_priv *priv = gpu->vendor_priv;
	char sysfs_path[128];
	struct file *f;
	const char *level_str;
	loff_t pos = 0;
	ssize_t n;

	if (!priv)
		return -EINVAL;

	switch (state) {
	case MVGAL_POWER_STATE_ACTIVE:
	case MVGAL_POWER_STATE_SUSTAINED:
		level_str = "auto";
		break;
	case MVGAL_POWER_STATE_IDLE:
		level_str = "low";
		break;
	case MVGAL_POWER_STATE_PARK:
	case MVGAL_POWER_STATE_OFF:
		level_str = "low";
		break;
	default:
		level_str = "auto";
		break;
	}

	snprintf(sysfs_path, sizeof(sysfs_path),
		 "/sys/bus/pci/devices/%04x:%02x:%02x.%u/power_dpm_force_performance_level",
		 pci_domain_nr(priv->pdev->bus),
		 priv->pdev->bus->number,
		 PCI_SLOT(priv->pdev->devfn),
		 PCI_FUNC(priv->pdev->devfn));

	f = filp_open(sysfs_path, O_WRONLY, 0);
	if (IS_ERR(f)) {
		/* Try the drm card path */
		snprintf(sysfs_path, sizeof(sysfs_path),
			 "/sys/class/drm/card%u/device/power_dpm_force_performance_level",
			 gpu->gpu_index);
		f = filp_open(sysfs_path, O_WRONLY, 0);
		if (IS_ERR(f)) {
			pr_debug("mvgal: AMD power state sysfs not available for GPU %u\n",
				 gpu->gpu_index);
			return 0; /* Non-fatal: sysfs may not be present on all kernels */
		}
	}

	n = kernel_write(f, level_str, strlen(level_str), &pos);
	filp_close(f, NULL);

	if (n < 0) {
		pr_warn("mvgal: AMD power state write failed for GPU %u: %zd\n",
			gpu->gpu_index, n);
		return (int)n;
	}

	strscpy(priv->power_profile, level_str, sizeof(priv->power_profile));
	pr_debug("mvgal: AMD GPU %u power state set to '%s'\n", gpu->gpu_index, level_str);
	return 0;
}

/**
 * mvgal_amd_export_dmabuf - Export AMD memory as DMA-BUF
 * 
 * Uses amdgpu_dma_buf_* functions.
 */
struct dma_buf *mvgal_amd_export_dmabuf(struct mvgal_gpu_device *gpu, uint64_t gpu_addr, size_t size)
{
	struct mvgal_amd_priv *priv = gpu->vendor_priv;

	if (!priv) {
		return ERR_PTR(-EINVAL);
	}

	if (!priv->can_export_dmabuf) {
		return ERR_PTR(-ENOTSUPP);
	}

	/* In the full implementation:
	 * 1. Get the GEM object from the address
	 * 2. Use drm_gem_prime_export() to create DMA-BUF
	 * 3. Or use amdgpu_dma_buf_create() if available
	 * 
	 * Study references:
	 * - drivers/gpu/drm/amd/amdgpu/amdgpu_dma_buf.c
	 * - drivers/gpu/drm/amd/amdgpu/amdgpu_gem.c
	 */

	pr_debug("MVGAL: AMD export_dmabuf (addr %016llx, size %zu)\n", gpu_addr, size);

	return ERR_PTR(-ENOSYS); /* Not yet implemented */
}

/**
 * mvgal_amd_import_dmabuf - Import DMA-BUF into AMD GPU
 */
int mvgal_amd_import_dmabuf(struct mvgal_gpu_device *gpu, struct dma_buf *buf, uint64_t *gpu_addr)
{
	struct mvgal_amd_priv *priv = gpu->vendor_priv;

	if (!priv || !buf) {
		return -EINVAL;
	}

	if (!priv->can_import_dmabuf) {
		return -ENOTSUPP;
	}

	/* Import requires DRM GEM access — not possible from this module context. */
	return -EOPNOTSUPP;
}

/**
 * mvgal_amd_query_utilization - Query AMD GPU utilization via sysfs
 *
 * Reads /sys/class/drm/cardN/device/gpu_busy_percent which is exported by
 * the amdgpu driver for all RDNA/GCN GPUs since kernel 4.19.
 */
int mvgal_amd_query_utilization(struct mvgal_gpu_device *gpu, uint32_t *util_percent)
{
	struct mvgal_amd_priv *priv = gpu->vendor_priv;
	char sysfs_path[128];
	struct file *f;
	char buf[16];
	loff_t pos = 0;
	ssize_t n;
	unsigned long val;
	int ret;

	if (!priv || !util_percent)
		return -EINVAL;

	/* Build the sysfs path from the PCI BDF string stored in the GPU slot.
	 * amdgpu exports gpu_busy_percent under the DRM card symlink. */
	snprintf(sysfs_path, sizeof(sysfs_path),
		 "/sys/bus/pci/devices/%04x:%02x:%02x.%u/gpu_busy_percent",
		 pci_domain_nr(priv->pdev->bus),
		 priv->pdev->bus->number,
		 PCI_SLOT(priv->pdev->devfn),
		 PCI_FUNC(priv->pdev->devfn));

	f = filp_open(sysfs_path, O_RDONLY, 0);
	if (IS_ERR(f)) {
		/* Fallback: try the drm card path */
		snprintf(sysfs_path, sizeof(sysfs_path),
			 "/sys/class/drm/card%u/device/gpu_busy_percent",
			 gpu->gpu_index);
		f = filp_open(sysfs_path, O_RDONLY, 0);
		if (IS_ERR(f)) {
			/* sysfs not available — return 0 rather than a fake value */
			*util_percent = 0;
			return 0;
		}
	}

	memset(buf, 0, sizeof(buf));
	n = kernel_read(f, buf, sizeof(buf) - 1, &pos);
	filp_close(f, NULL);

	if (n <= 0) {
		*util_percent = 0;
		return 0;
	}

	ret = kstrtoul(buf, 10, &val);
	if (ret != 0) {
		*util_percent = 0;
		return 0;
	}

	*util_percent = (uint32_t)min(val, 100UL);
	return 0;
}
