cirrus显卡驱动笔记

冰山一脚20132026-10-01 13:10

cirrus显卡未实现双 VRAM scanout buffer，若显示控制器正在扫描某一帧时，CPU 向 VRAM 写入了这帧的一部分，就可能看到上半部分是旧像素、下半部分是新像素，画面撕裂，即 tearing（撕裂）。
文件作用

* drivers/gpu/drm/tiny/Kconfig (line 26)(D:/study/official/linux-6.10.14/drivers/gpu/drm/tiny/Kconfig:26)：定义 CONFIG_DRM_CIRRUS_QEMU，依赖 DRM && PCI && MMU，并选择 DRM_KMS_HELPER、DRM_GEM_SHMEM_HELPER。
* drivers/gpu/drm/tiny/Makefile (line 5)(D:/study/official/linux-6.10.14/drivers/gpu/drm/tiny/Makefile:5)：把该配置编译为 cirrus.o。
* include/video/cirrus.h(D:/study/official/linux-6.10.14/include/video/cirrus.h)：Cirrus 寄存器/硬件定义。
* include/video/vga.h(D:/study/official/linux-6.10.14/include/video/vga.h)：通用 VGA 寄存器定义。
注意此驱动只适用于 QEMU 模拟的 Cirrus 5446，不是实际 Cirrus 显卡驱动。cirrus.c 已经把 plane/CRTC/encoder/connector、PCI probe、VRAM/MMIO 映射和 fbdev 支持都实现了，因此不需要额外的 cirrus_*.c 私有源文件。BAR的作用如下：
cirrus->vram // BAR0：硬件扫描的显存
cirrus->mmio // BAR1：Cirrus 寄存器
1、核心结构体

cpp 复制代码 
struct cirrus_device {
    struct drm_device          dev;
    /* modesetting pipeline */
    struct drm_plane           primary_plane;
    struct drm_crtc            crtc;
    struct drm_encoder         encoder;
    struct drm_connector           connector;

    /* HW resources */
    void __iomem               *vram;  // 图像数据
    void __iomem               *mmio;  // 控制寄存器
};

#define to_cirrus(_dev) container_of(_dev, struct cirrus_device, dev)

// 保存状态数据：格式 和 行位数（stride）
static const uint32_t cirrus_primary_plane_formats[] = {
    DRM_FORMAT_RGB565,
    DRM_FORMAT_RGB888,
    DRM_FORMAT_XRGB8888,
};

static const uint64_t cirrus_primary_plane_format_modifiers[] = {
    DRM_FORMAT_MOD_LINEAR,
    DRM_FORMAT_MOD_INVALID
};

struct cirrus_primary_plane_state {
    struct drm_shadow_plane_state base;
    /* HW scanout buffer */
    const struct drm_format_info   *format;
    unsigned int               pitch; // 目标行跨度
};

static inline struct cirrus_primary_plane_state *
to_cirrus_primary_plane_state(struct drm_plane_state *plane_state)
{
    return container_of(plane_state, struct cirrus_primary_plane_state, base.base);
};

2、cirrus驱动注册

cpp 复制代码 
// 匹配表
static const struct pci_device_id pciidlist[] = {
    {
        .vendor    = PCI_VENDOR_ID_CIRRUS,
        .device    = PCI_DEVICE_ID_CIRRUS_5446,
        /* only bind to the cirrus chip in qemu */
        .subvendor = PCI_SUBVENDOR_ID_REDHAT_QUMRANET,
        .subdevice = PCI_SUBDEVICE_ID_QEMU,
    }, {
        .vendor    = PCI_VENDOR_ID_CIRRUS,
        .device    = PCI_DEVICE_ID_CIRRUS_5446,
        .subvendor = PCI_VENDOR_ID_XEN,
        .subdevice = 0x0001,
    },
    { /* end if list */ }
};

static struct pci_driver cirrus_pci_driver = {
    .name = DRIVER_NAME,
    .id_table = pciidlist,
    .probe = cirrus_pci_probe,
    .remove = cirrus_pci_remove,
    .shutdown = cirrus_pci_shutdown,
};

drm_module_pci_driver(cirrus_pci_driver)
MODULE_DEVICE_TABLE(pci, pciidlist);
MODULE_LICENSE("GPL");

3、核心加载probe：注册drm并初始化参数，建立显示管道(framebuffer, plane, crtc, encoder, connector)。

cpp 复制代码 
DEFINE_DRM_GEM_FOPS(cirrus_fops);

static const struct drm_driver cirrus_driver = {
    .driver_features = DRIVER_MODESET | DRIVER_GEM | DRIVER_ATOMIC,

    .name        = DRIVER_NAME,
    .desc        = DRIVER_DESC,
    .date        = DRIVER_DATE,
    .major       = DRIVER_MAJOR,
    .minor       = DRIVER_MINOR,
    .fops        = &cirrus_fops,
    DRM_GEM_SHMEM_DRIVER_OPS,
};

static int cirrus_pci_probe(struct pci_dev *pdev,
                const struct pci_device_id *ent)
{
    struct drm_device *dev;
    struct cirrus_device *cirrus;
    int ret;

    ret = drm_aperture_remove_conflicting_pci_framebuffers(pdev, &cirrus_driver);
    if (ret)
        return ret;

    ret = pcim_enable_device(pdev);
    if (ret)
        return ret;

    ret = pci_request_regions(pdev, DRIVER_NAME);
    if (ret)
        return ret;

    ret = -ENOMEM;
    cirrus = devm_drm_dev_alloc(&pdev->dev, &cirrus_driver, struct cirrus_device, dev);
    if (IS_ERR(cirrus))
        return PTR_ERR(cirrus);

    dev = &cirrus->dev;
    cirrus->vram = devm_ioremap(&pdev->dev, pci_resource_start(pdev, 0), pci_resource_len(pdev, 0));
    if (cirrus->vram == NULL)
        return -ENOMEM;

    cirrus->mmio = devm_ioremap(&pdev->dev, pci_resource_start(pdev, 1), pci_resource_len(pdev, 1));
    if (cirrus->mmio == NULL)
        return -ENOMEM;

    ret = cirrus_mode_config_init(cirrus);
    if (ret)
        return ret;

    ret = cirrus_pipe_init(cirrus);
    if (ret < 0)
        return ret;

    drm_mode_config_reset(dev);

    pci_set_drvdata(pdev, dev);
    ret = drm_dev_register(dev, 0);
    if (ret)
        return ret;

    drm_fbdev_generic_setup(dev, 16);
    return 0;
}

4、模式配置初始化

cpp 复制代码 
static const struct drm_mode_config_funcs cirrus_mode_config_funcs = {
    .fb_create = drm_gem_fb_create_with_dirty,
    .mode_valid = cirrus_mode_config_mode_valid,
    .atomic_check = drm_atomic_helper_check,
    .atomic_commit = drm_atomic_helper_commit,
};

static int cirrus_mode_config_init(struct cirrus_device *cirrus)
{
    struct drm_device *dev = &cirrus->dev;
    int ret;
    ret = drmm_mode_config_init(dev);
    if (ret)
        return ret;

    dev->mode_config.min_width = 0;
    dev->mode_config.min_height = 0;
    dev->mode_config.max_width = CIRRUS_MAX_PITCH / 2;
    dev->mode_config.max_height = 1024;
    dev->mode_config.preferred_depth = 16;
    dev->mode_config.prefer_shadow = 0;
    dev->mode_config.funcs = &cirrus_mode_config_funcs;
    return 0;
}

5、核心显示管道建立

cpp 复制代码 
static int cirrus_pipe_init(struct cirrus_device *cirrus)
{
    struct drm_device *dev = &cirrus->dev;
    struct drm_plane *primary_plane;
    struct drm_crtc *crtc;
    struct drm_encoder *encoder;
    struct drm_connector *connector;
    int ret;

    // 创建primary plane
    primary_plane = &cirrus->primary_plane;
    ret = drm_universal_plane_init(dev, primary_plane, 0,
                       &cirrus_primary_plane_funcs,
                       cirrus_primary_plane_formats,
                       ARRAY_SIZE(cirrus_primary_plane_formats),
                       cirrus_primary_plane_format_modifiers,
                       DRM_PLANE_TYPE_PRIMARY, NULL);
    if (ret)
        return ret;

    // plane回调处理函数
    drm_plane_helper_add(primary_plane, &cirrus_primary_plane_helper_funcs);
    drm_plane_enable_fb_damage_clips(primary_plane);

    // 与primary_plane绑定的crtc回调处理函数
    crtc = &cirrus->crtc;
    ret = drm_crtc_init_with_planes(dev, crtc, primary_plane, NULL, &cirrus_crtc_funcs, NULL);
    if (ret)
        return ret;
    drm_crtc_helper_add(crtc, &cirrus_crtc_helper_funcs);

    // encoder回调处理函数
    encoder = &cirrus->encoder;
    ret = drm_encoder_init(dev, encoder, &cirrus_encoder_funcs, DRM_MODE_ENCODER_DAC, NULL);
    if (ret)
        return ret;

    // 与CRTC绑定
    encoder->possible_crtcs = drm_crtc_mask(crtc);

    // connector回调处理函数
    connector = &cirrus->connector;
    ret = drm_connector_init(dev, connector, &cirrus_connector_funcs, DRM_MODE_CONNECTOR_VGA);
    if (ret)
        return ret;
    drm_connector_helper_add(connector, &cirrus_connector_helper_funcs);

    // connector与encoder绑定
    ret = drm_connector_attach_encoder(connector, encoder);
    if (ret)
        return ret;
    return 0;
}

5.1、plane处理函数

cpp 复制代码 
static const struct drm_plane_funcs cirrus_primary_plane_funcs = {
    .update_plane = drm_atomic_helper_update_plane,    // drm默认回调函数
    .disable_plane = drm_atomic_helper_disable_plane,  // drm默认回调函数
    .destroy = drm_plane_cleanup,                      // drm默认回调函数
    .reset = cirrus_reset_primary_plane,
    .atomic_duplicate_state = cirrus_primary_plane_atomic_duplicate_state, 
    .atomic_destroy_state = cirrus_primary_plane_atomic_destroy_state,
};

static const struct drm_plane_helper_funcs cirrus_primary_plane_helper_funcs = {
    DRM_GEM_SHADOW_PLANE_HELPER_FUNCS,
    .atomic_check = cirrus_primary_plane_helper_atomic_check,
    .atomic_update = cirrus_primary_plane_helper_atomic_update,
};

5.1.1、cirrus_primary_plane_funcs回调处理函数

cpp 复制代码 
static struct drm_plane_state *cirrus_primary_plane_atomic_duplicate_state(struct drm_plane *plane)
{
    struct drm_plane_state *plane_state = plane->state;
    struct cirrus_primary_plane_state *primary_plane_state = to_cirrus_primary_plane_state(plane_state);
    struct cirrus_primary_plane_state *new_primary_plane_state;
    struct drm_shadow_plane_state *new_shadow_plane_state;
    if (!plane_state)
        return NULL;

    new_primary_plane_state = kzalloc(sizeof(*new_primary_plane_state), GFP_KERNEL);
    if (!new_primary_plane_state)
        return NULL;

    new_shadow_plane_state = &new_primary_plane_state->base;
    __drm_gem_duplicate_shadow_plane_state(plane, new_shadow_plane_state);
    new_primary_plane_state->format = primary_plane_state->format;
    new_primary_plane_state->pitch = primary_plane_state->pitch;
    return &new_shadow_plane_state->base;
}

static void cirrus_primary_plane_atomic_destroy_state(struct drm_plane *plane, struct drm_plane_state *plane_state)
{
    struct cirrus_primary_plane_state *primary_plane_state = to_cirrus_primary_plane_state(plane_state);
    __drm_gem_destroy_shadow_plane_state(&primary_plane_state->base);
    kfree(primary_plane_state);
}

static void cirrus_reset_primary_plane(struct drm_plane *plane)
{
    struct cirrus_primary_plane_state *primary_plane_state;
    if (plane->state) {
        cirrus_primary_plane_atomic_destroy_state(plane, plane->state);
        plane->state = NULL; /* must be set to NULL here */
    }
    primary_plane_state = kzalloc(sizeof(*primary_plane_state), GFP_KERNEL);
    if (!primary_plane_state)
        return;
    __drm_gem_reset_shadow_plane(plane, &primary_plane_state->base);
}

5.1.2、plane的helper原子提交具体处理函数

cpp 复制代码 
static int cirrus_primary_plane_helper_atomic_check(struct drm_plane *plane, struct drm_atomic_state *state)
{
    struct drm_plane_state *new_plane_state = drm_atomic_get_new_plane_state(state, plane);
    struct cirrus_primary_plane_state *new_primary_plane_state = to_cirrus_primary_plane_state(new_plane_state);
    struct drm_framebuffer *fb = new_plane_state->fb;
    struct drm_crtc *new_crtc = new_plane_state->crtc;
    struct drm_crtc_state *new_crtc_state = NULL;
    int ret;
    unsigned int pitch;

    if (new_crtc)
        new_crtc_state = drm_atomic_get_new_crtc_state(state, new_crtc);

    ret = drm_atomic_helper_check_plane_state(new_plane_state, new_crtc_state,
                          DRM_PLANE_NO_SCALING,
                          DRM_PLANE_NO_SCALING,
                          false, false);
    if (ret)
        return ret;
    else if (!new_plane_state->visible)
        return 0;

    pitch = cirrus_pitch(fb);

    /* validate size constraints */
    if (pitch > CIRRUS_MAX_PITCH)
        return -EINVAL;
    else if (pitch * fb->height > CIRRUS_VRAM_SIZE)
        return -EINVAL;

    new_primary_plane_state->format = cirrus_format(fb);
    new_primary_plane_state->pitch = pitch;
    return 0;
}

static void cirrus_primary_plane_helper_atomic_update(struct drm_plane *plane, struct drm_atomic_state *state)
{
    struct cirrus_device *cirrus = to_cirrus(plane->dev);
    struct drm_plane_state *plane_state = drm_atomic_get_new_plane_state(state, plane);
    struct cirrus_primary_plane_state *primary_plane_state = to_cirrus_primary_plane_state(plane_state);
    struct drm_shadow_plane_state *shadow_plane_state = to_drm_shadow_plane_state(plane_state);
    struct drm_framebuffer *fb = plane_state->fb;
    const struct drm_format_info *format = primary_plane_state->format;
    unsigned int pitch = primary_plane_state->pitch;
    struct drm_plane_state *old_plane_state = drm_atomic_get_old_plane_state(state, plane);
    struct cirrus_primary_plane_state *old_primary_plane_state = to_cirrus_primary_plane_state(old_plane_state);
    // 获取显存地址
    struct iosys_map vaddr = IOSYS_MAP_INIT_VADDR_IOMEM(cirrus->vram);
    struct drm_atomic_helper_damage_iter iter;
    struct drm_rect damage;
    int idx;

    if (!fb)
        return;
    if (!drm_dev_enter(&cirrus->dev, &idx))
        return;

    if (old_primary_plane_state->format != format)
        cirrus_format_set(cirrus, format);
    if (old_primary_plane_state->pitch != pitch)
        cirrus_pitch_set(cirrus, pitch);
    // 准备 damage 迭代器和单个矩形变量。damage 是"此次 framebuffer 真正发生改变的矩形区域"，如只改动鼠标附近的一小块，就没有必要复制整个屏幕。
    drm_atomic_helper_damage_iter_init(&iter, old_plane_state, plane_state);
    drm_atomic_for_each_plane_damage(&iter, &damage) {
        // offset = damage.y1 × pitch + damage.x1 × 每像素字节数
        unsigned int offset = drm_fb_clip_offset(pitch, format, &damage);
        // 加上偏移量
        struct iosys_map dst = IOSYS_MAP_INIT_OFFSET(&vaddr, offset);
        // 拷贝到显存
        drm_fb_blit(&dst, &pitch, format->format, shadow_plane_state->data, fb, &damage, &shadow_plane_state->fmtcnv_state);
    }

    drm_dev_exit(idx);
}

5.2、crtc处理函数

cpp 复制代码 
static const struct drm_crtc_helper_funcs cirrus_crtc_helper_funcs = {
    .atomic_check = cirrus_crtc_helper_atomic_check,
    .atomic_enable = cirrus_crtc_helper_atomic_enable,
};

static const struct drm_crtc_funcs cirrus_crtc_funcs = {
    .reset = drm_atomic_helper_crtc_reset,           // drm默认回调函数
    .destroy = drm_crtc_cleanup,                     // drm默认回调函数
    .set_config = drm_atomic_helper_set_config,      // drm默认回调函数
    .page_flip = drm_atomic_helper_page_flip,        // drm默认回调函数
    .atomic_duplicate_state = drm_atomic_helper_crtc_duplicate_state,  // drm默认回调函数
    .atomic_destroy_state = drm_atomic_helper_crtc_destroy_state,      // drm默认回调函数
};

crtc原子提交具体处理函数

cpp 复制代码 
static int cirrus_crtc_helper_atomic_check(struct drm_crtc *crtc, struct drm_atomic_state *state)
{
    struct drm_crtc_state *crtc_state = drm_atomic_get_new_crtc_state(state, crtc);
    int ret;

    if (!crtc_state->enable)
        return 0;
    ret = drm_atomic_helper_check_crtc_primary_plane(crtc_state);
    if (ret)
        return ret;
    return 0;
}

static void cirrus_crtc_helper_atomic_enable(struct drm_crtc *crtc, struct drm_atomic_state *state)
{
    struct cirrus_device *cirrus = to_cirrus(crtc->dev);
    struct drm_crtc_state *crtc_state = drm_atomic_get_new_crtc_state(state, crtc);
    int idx;

    if (!drm_dev_enter(&cirrus->dev, &idx))
        return;
    cirrus_mode_set(cirrus, &crtc_state->mode);

    /* Unblank (needed on S3 resume, vgabios doesn't do it then) */
    outb(VGA_AR_ENABLE_DISPLAY, VGA_ATT_W);
    drm_dev_exit(idx);
}

5.3、encoder处理函数

cpp 复制代码 
static const struct drm_encoder_funcs cirrus_encoder_funcs = {
    .destroy = drm_encoder_cleanup,
};

5.4、connector处理函数

cpp 复制代码 
static const struct drm_connector_helper_funcs cirrus_connector_helper_funcs = {
    .get_modes = cirrus_connector_helper_get_modes,
};

static const struct drm_connector_funcs cirrus_connector_funcs = {
    .fill_modes = drm_helper_probe_single_connector_modes,                 // drm默认回调函数
    .destroy = drm_connector_cleanup,                                      // drm默认回调函数
    .reset = drm_atomic_helper_connector_reset,                            // drm默认回调函数
    .atomic_duplicate_state = drm_atomic_helper_connector_duplicate_state, // drm默认回调函数
    .atomic_destroy_state = drm_atomic_helper_connector_destroy_state,     // drm默认回调函数
};

crtc原子提交具体处理函数

cpp 复制代码 
static int cirrus_connector_helper_get_modes(struct drm_connector *connector)
{
    int count;
    count = drm_add_modes_noedid(connector, connector->dev->mode_config.max_width, connector->dev->mode_config.max_height);
    drm_set_preferred_mode(connector, 1024, 768);
    return count;
}
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