//! User-space device access: enumerate the kernel's device table, claim a device,
//! map its MMIO, and bind its interrupt. A driver uses these to find and take
//! ownership of its hardware; the claim is the capability the kernel checks before
//! mapping registers or routing an IRQ.

const std = @import("std");
const abi = @import("abi");
const device_abi = @import("device-abi");
const sc = @import("system-call.zig");

pub const DeviceDescriptor = device_abi.DeviceDescriptor;
pub const ResourceDescriptor = device_abi.ResourceDescriptor;
pub const DeviceClass = device_abi.DeviceClass;
pub const ResourceKind = device_abi.ResourceKind;

inline fn failed(r: usize) bool {
    return r > ~@as(usize, 0) - 4095;
}

/// Copy up to `buffer.len` device descriptors into `buffer`; returns the total count.
pub fn enumerate(buffer: []DeviceDescriptor) usize {
    return sc.systemCall2(.device_enumerate, @intFromPtr(buffer.ptr), buffer.len);
}

/// Take exclusive ownership of device `id`. Returns false if taken or invalid.
pub fn claim(id: u64) bool {
    return !failed(sc.systemCall1(.device_claim, id));
}

/// Map resource `resource_index` (which must be an MMIO window) of claimed device
/// `device_id` into this address space; returns the register base virtual address.
pub fn mmioMap(device_id: u64, resource_index: u64) ?usize {
    const r = sc.systemCall2(.mmio_map, device_id, resource_index);
    return if (failed(r)) null else r;
}

/// `DeviceDescriptor.parent` for a device with no parent.
pub const no_parent = device_abi.no_parent;

/// `DeviceDescriptor.pci_class` for a device that is not a PCI function. Set this on
/// descriptors passed to `register` unless the child really is one.
pub const no_pci_class = device_abi.no_pci_class;

/// Publish `descriptor` as a child of `parent_id`, which this process must have claimed.
/// Returns the new device id. The child is left unclaimed, so whichever driver owns
/// that class of device can `claim` it — that is how a bus hands off a device.
///
/// Every resource in `descriptor` must be **contained** in a parent resource of the same
/// kind: a sub-window of the parent's MMIO, or one of its IRQs. The kernel refuses
/// anything else, because a device descriptor is a licence to map physical memory and
/// a bus driver may only subdivide what it already owns. `descriptor.id` and `descriptor.parent`
/// are ignored. A device with no resources at all is fine — a USB device is reached
/// through its controller, not by MMIO.
pub fn register(parent_id: u64, descriptor: *const DeviceDescriptor) ?u64 {
    const r = sc.systemCall2(.device_register, parent_id, @intFromPtr(descriptor));
    return if (failed(r)) null else r;
}

/// Bind resource `resource_index` (which must be an IRQ) of claimed device `device_id` to
/// `endpoint`. From then on the interrupt arrives as an asynchronous notification:
/// `ipc.replyWait` on that endpoint returns with the high bit set in `badge` and the
/// low bits carrying the GSI. The kernel masks the line before waking you.
pub fn irqBind(device_id: u64, resource_index: u64, endpoint: usize) bool {
    return !failed(sc.systemCall3(.irq_bind, device_id, resource_index, endpoint));
}

/// Re-arm a bound IRQ. Call this **after** quieting the device (clearing whatever
/// status register holds its line asserted) — the kernel left the line masked
/// precisely because it could not do that for you. Skip it and the interrupt never
/// fires again; call it before the device is quiet and a level-triggered line storms.
pub fn irqAck(device_id: u64, resource_index: u64) bool {
    return !failed(sc.systemCall2(.irq_ack, device_id, resource_index));
}

/// The Message-Signalled Interrupt address/data a driver programs into its device's
/// MSI capability. The device raises the interrupt by writing `data` to `address`.
pub const Msi = struct { address: u64, data: u32 };

/// Set up MSI for a claimed device: the kernel allocates a per-device edge-triggered
/// vector, binds it to `endpoint` (delivered like `irqBind`, but with no mask and no
/// `irqAck` cycle), and returns the (address, data) to write into the device's MSI
/// capability — found by mmio_mapping the device's ECAM config space (resource 0) and
/// walking its capability list. Returns null on failure. Two return values (address in
/// rax, data in rdx), so a hand-written stub.
pub fn msiBind(device_id: u64, endpoint: usize) ?Msi {
    var rax: usize = undefined;
    var rdx: usize = undefined;
    asm volatile ("syscall"
        : [rax] "={rax}" (rax),
          [rdx] "={rdx}" (rdx),
        : [n] "{rax}" (@intFromEnum(abi.SystemCall.msi_bind)),
          [a0] "{rdi}" (device_id),
          [a1] "{rsi}" (endpoint),
        : .{ .rcx = true, .r11 = true, .memory = true });
    if (failed(rax)) return null;
    return .{ .address = rax, .data = @intCast(rdx) };
}

/// Read `width` bytes (1, 2, or 4) from a port in a claimed device's `io_port`
/// resource, at byte `offset` within it. Ring 3 has no direct `in`/`out`, so a legacy
/// driver (PS/2, 16550 UART) reaches its ports through this claim-gated call — each
/// access is a syscall, which is fine for the low-rate hardware that needs it. Returns
/// null if the capability check fails (device not claimed, wrong resource, out of
/// range). A device that decodes no data returns all-ones, which is a valid value, not
/// a failure.
pub fn ioRead(device_id: u64, resource_index: u64, offset: u64, width: u8) ?u32 {
    const r = sc.systemCall4(.io_read, device_id, resource_index, offset, width);
    return if (failed(r)) null else @intCast(r);
}

/// Write `value` (its low `width` bytes, 1/2/4) to a port in a claimed device's
/// `io_port` resource, at byte `offset`. Same capability gate as `ioRead`.
pub fn ioWrite(device_id: u64, resource_index: u64, offset: u64, width: u8, value: u32) bool {
    return !failed(sc.systemCall5(.io_write, device_id, resource_index, offset, width, value));
}

/// Find DeviceDescription by hid
///
/// Utility function for driver development
pub fn findDeviceDescriptorByHid(buffer: []DeviceDescriptor, hid_needle: []const u8) ?DeviceDescriptor {
    const total = enumerate(buffer);
    const n = @min(total, buffer.len);
    for (@as([]DeviceDescriptor, buffer[0..n])) |d| {
        const hid_haystack = d.hid[0..@intCast(d.hid_len)];
        if (std.mem.eql(u8, hid_haystack, hid_needle)) {
            return d;
        }
    }

    return null;
}
