sdk/fidl/fuchsia.hardware.sysmem/metadata.fidl

// Copyright 2021 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
library fuchsia.hardware.sysmem;

/// This is the sysmem driver metadata type. See also
/// [`fuchsia.hardware.sysmem/Metadata`].
const METADATA_TYPE uint32 = 0x53794d64; // 0x53794d00 | DEVICE_METADATA_PRIVATE

/// Driver metadata for the sysmem driver.
type Metadata = table {
    1: vid uint32;
    2: pid uint32;

    // protected_memory_size
    // contiguous_memory_size
    //
    // Positive values are interpreted as bytes, and are aligned up to next
    // ZX_PAGE_SIZE.
    //
    // Negative values are interpreted as a percentage of physical memory (after
    // negation), and resulting size in bytes is aligned up to next ZX_PAGE_SIZE.

    /// protected_memory_size
    ///
    /// Size of the protected memory pool.
    ///
    /// Positive values are interpreted as bytes, and are aligned up to next
    /// ZX_PAGE_SIZE.
    ///
    /// Negative values are interpreted as a percentage of physical memory
    /// (after negation), and resulting size in bytes is aligned up to next
    /// ZX_PAGE_SIZE.
    ///
    /// un-set or 0 means there is no protected memory pool.
    3: protected_memory_size int64;

    /// contiguous_memory_size
    ///
    /// Size of the pool used to allocate contiguous memory.
    ///
    /// Positive values are interpreted as bytes, and are aligned up to next
    /// ZX_PAGE_SIZE.
    ///
    /// Negative values are interpreted as a percentage of physical memory
    /// (after negation), and resulting size in bytes is aligned up to next
    /// ZX_PAGE_SIZE.
    ///
    /// Un-set or zero means no space is reserved up front, which will end up
    /// using zx::vmo::create_contiguous() for each allocation instead of
    /// allocating up front, which can be prone to failure when physical memory
    /// becomes fragmented.
    ///
    /// There is no fallback from pre-reserved to zx::vmo::create_contiguous().
    /// If we're pre-reserving memory, we should reserve enough.
    4: contiguous_memory_size int64;
};