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Linux 内核 ASoC 框架,在概念上将嵌入式音频系统拆分为多个可复用的组件驱动程序,包括 Codec 类驱动程序、平台类驱动程序和机器类驱动程序。在实现上,机器类驱动程序用 struct snd_soc_card 和 struct snd_soc_dai_link 结构描述,属于平台类驱动程序的 DMA 引擎驱动程序由 struct snd_soc_component_driver 结构描述,codec 类驱动程序和 I2S 等驱动程序,由 struct snd_soc_component_driver、struct snd_soc_dai_driver 和 struct snd_soc_dai_ops 等结构描述。除平台类驱动程序外的各种驱动程序都通过 component 抽象组织在一起,即这些驱动程序都作为 struct snd_soc_component_driver 注册给 Linux 内核 ASoC 框架,Linux 内核 ASoC 框架为它们各自创建 struct snd_soc_component 结构对象,并保存在 sound/soc/soc-core.c 文件中定义的全局链表 component_list 中。
一个 DMA 驱动程序的示例为 soc/pxa/pxa2xx-pcm.c:- static const struct snd_soc_component_driver pxa2xx_soc_platform = {
- .pcm_construct = pxa2xx_soc_pcm_new,
- .pcm_destruct = pxa2xx_soc_pcm_free,
- .open = pxa2xx_soc_pcm_open,
- .close = pxa2xx_soc_pcm_close,
- .hw_params = pxa2xx_soc_pcm_hw_params,
- .hw_free = pxa2xx_soc_pcm_hw_free,
- .prepare = pxa2xx_soc_pcm_prepare,
- .trigger = pxa2xx_soc_pcm_trigger,
- .pointer = pxa2xx_soc_pcm_pointer,
- .mmap = pxa2xx_soc_pcm_mmap,
- };
- static int pxa2xx_soc_platform_probe(struct platform_device *pdev)
- {
- return devm_snd_soc_register_component(&pdev->dev, &pxa2xx_soc_platform,
- NULL, 0);
- }
- static struct platform_driver pxa_pcm_driver = {
- .driver = {
- .name = "pxa-pcm-audio",
- },
- .probe = pxa2xx_soc_platform_probe,
- };
- module_platform_driver(pxa_pcm_driver);
复制代码 DMA 引擎驱动程序和 I2S 或 Codec 驱动程序一样,通过 devm_snd_soc_register_component() 函数以 struct snd_soc_component_driver 的形式注册给 Linux 内核 ASoC 框架,但比较特别的地方在于,它的 dai driver 参数为空。
机器类驱动程序定义的 struct snd_soc_dai_link 结构对象通过 struct snd_soc_dai_link_component 描述它引用的其它类型的驱动程序,如机器类驱动程序 sound/soc/pxa/e800_wm9712.c 有如下的代码片段:- SND_SOC_DAILINK_DEFS(ac97,
- DAILINK_COMP_ARRAY(COMP_CPU("pxa2xx-ac97")),
- DAILINK_COMP_ARRAY(COMP_CODEC("wm9712-codec", "wm9712-hifi")),
- DAILINK_COMP_ARRAY(COMP_PLATFORM("pxa-pcm-audio")));
- SND_SOC_DAILINK_DEFS(ac97_aux,
- DAILINK_COMP_ARRAY(COMP_CPU("pxa2xx-ac97-aux")),
- DAILINK_COMP_ARRAY(COMP_CODEC("wm9712-codec", "wm9712-aux")),
- DAILINK_COMP_ARRAY(COMP_PLATFORM("pxa-pcm-audio")));
- static struct snd_soc_dai_link e800_dai[] = {
- {
- .name = "AC97",
- .stream_name = "AC97 HiFi",
- SND_SOC_DAILINK_REG(ac97),
- },
- {
- .name = "AC97 Aux",
- .stream_name = "AC97 Aux",
- SND_SOC_DAILINK_REG(ac97_aux),
- },
- };
- static struct snd_soc_card e800 = {
- .name = "Toshiba e800",
- .owner = THIS_MODULE,
- .dai_link = e800_dai,
- .num_links = ARRAY_SIZE(e800_dai),
- .dapm_widgets = e800_dapm_widgets,
- .num_dapm_widgets = ARRAY_SIZE(e800_dapm_widgets),
- .dapm_routes = audio_map,
- .num_dapm_routes = ARRAY_SIZE(audio_map),
- };
复制代码 SND_SOC_DAILINK_DEFS() 宏用于为 struct snd_soc_dai_link 方便地定义引用的 cpus、codecs 和 platforms 等 struct snd_soc_dai_link_component 数组,其中用于定义 platforms 的 DAILINK_COMP_ARRAY(COMP_PLATFORM("pxa-pcm-audio")) 引用了上面我们看到的 DMA 引擎驱动。
Linux 内核 ASoC 框架提供了一个通用的 DMA 引擎驱动程序,位于文件 sound/soc/soc-generic-dmaengine-pcm 中。这个驱动程序本身不会主动向 Linux 内核 ASoC 框架注册自己,需要使用 DMA 引擎在设备和内存之间传数据的驱动程序要在 probe 时注册它,如 sound/soc/rockchip/rockchip_pcm.c:- static const struct snd_pcm_hardware snd_rockchip_hardware = {
- .info = SNDRV_PCM_INFO_MMAP |
- SNDRV_PCM_INFO_MMAP_VALID |
- SNDRV_PCM_INFO_PAUSE |
- SNDRV_PCM_INFO_RESUME |
- SNDRV_PCM_INFO_INTERLEAVED,
- .period_bytes_min = 32,
- .period_bytes_max = 8192,
- .periods_min = 1,
- .periods_max = 52,
- .buffer_bytes_max = 64 * 1024,
- .fifo_size = 32,
- };
- static const struct snd_dmaengine_pcm_config rk_dmaengine_pcm_config = {
- .pcm_hardware = &snd_rockchip_hardware,
- .prepare_slave_config = snd_dmaengine_pcm_prepare_slave_config,
- .prealloc_buffer_size = 32 * 1024,
- };
- int rockchip_pcm_platform_register(struct device *dev)
- {
- return devm_snd_dmaengine_pcm_register(dev, &rk_dmaengine_pcm_config,
- SND_DMAENGINE_PCM_FLAG_COMPAT);
- }
- EXPORT_SYMBOL_GPL(rockchip_pcm_platform_register);
复制代码 这里的 rockchip_pcm_platform_register() 函数在 I2S 驱动程序的 probe 操作 (位于 sound/soc/rockchip/rockchip_i2s.c) 中调用:- static int rockchip_i2s_probe(struct platform_device *pdev)
- {
- . . . . . .
- ret = devm_snd_soc_register_component(&pdev->dev,
- &rockchip_i2s_component,
- soc_dai, 1);
- if (ret) {
- dev_err(&pdev->dev, "Could not register DAI\n");
- goto err_suspend;
- }
- ret = rockchip_pcm_platform_register(&pdev->dev);
- if (ret) {
- dev_err(&pdev->dev, "Could not register PCM\n");
- goto err_suspend;
- }
- return 0;
- . . . . . .
- return ret;
- }
复制代码 rockchip_pcm_platform_register() 函数调用 devm_snd_dmaengine_pcm_register() 函数注册通用 DMA 引擎驱动程序。devm_snd_dmaengine_pcm_register() 函数定义 (位于 sound/soc/soc-devres.c) 如下:- static void devm_dmaengine_pcm_release(struct device *dev, void *res)
- {
- snd_dmaengine_pcm_unregister(*(struct device **)res);
- }
- /**
- * devm_snd_dmaengine_pcm_register - resource managed dmaengine PCM registration
- * @dev: The parent device for the PCM device
- * @config: Platform specific PCM configuration
- * @flags: Platform specific quirks
- *
- * Register a dmaengine based PCM device with automatic unregistration when the
- * device is unregistered.
- */
- int devm_snd_dmaengine_pcm_register(struct device *dev,
- const struct snd_dmaengine_pcm_config *config, unsigned int flags)
- {
- struct device **ptr;
- int ret;
- ptr = devres_alloc(devm_dmaengine_pcm_release, sizeof(*ptr), GFP_KERNEL);
- if (!ptr)
- return -ENOMEM;
- ret = snd_dmaengine_pcm_register(dev, config, flags);
- if (ret == 0) {
- *ptr = dev;
- devres_add(dev, ptr);
- } else {
- devres_free(ptr);
- }
- return ret;
- }
- EXPORT_SYMBOL_GPL(devm_snd_dmaengine_pcm_register);
- #endif
复制代码 devm_snd_dmaengine_pcm_register() 函数和之前看到的devm_snd_soc_register_card() 与 devm_snd_soc_register_component() 函数一样,只是它封装的是 snd_dmaengine_pcm_register() 函数。snd_dmaengine_pcm_register() 函数定义 (位于 sound/soc/soc-generic-dmaengine-pcm.c) 如下:- static const struct snd_soc_component_driver dmaengine_pcm_component = {
- .name = SND_DMAENGINE_PCM_DRV_NAME,
- .probe_order = SND_SOC_COMP_ORDER_LATE,
- .open = dmaengine_pcm_open,
- .close = dmaengine_pcm_close,
- .hw_params = dmaengine_pcm_hw_params,
- .trigger = dmaengine_pcm_trigger,
- .pointer = dmaengine_pcm_pointer,
- .pcm_construct = dmaengine_pcm_new,
- };
- static const struct snd_soc_component_driver dmaengine_pcm_component_process = {
- .name = SND_DMAENGINE_PCM_DRV_NAME,
- .probe_order = SND_SOC_COMP_ORDER_LATE,
- .open = dmaengine_pcm_open,
- .close = dmaengine_pcm_close,
- .hw_params = dmaengine_pcm_hw_params,
- .trigger = dmaengine_pcm_trigger,
- .pointer = dmaengine_pcm_pointer,
- .copy_user = dmaengine_copy_user,
- .pcm_construct = dmaengine_pcm_new,
- };
- static const char * const dmaengine_pcm_dma_channel_names[] = {
- [SNDRV_PCM_STREAM_PLAYBACK] = "tx",
- [SNDRV_PCM_STREAM_CAPTURE] = "rx",
- };
- static int dmaengine_pcm_request_chan_of(struct dmaengine_pcm *pcm,
- struct device *dev, const struct snd_dmaengine_pcm_config *config)
- {
- unsigned int i;
- const char *name;
- struct dma_chan *chan;
- if ((pcm->flags & SND_DMAENGINE_PCM_FLAG_NO_DT) || (!dev->of_node &&
- !(config && config->dma_dev && config->dma_dev->of_node)))
- return 0;
- if (config && config->dma_dev) {
- /*
- * If this warning is seen, it probably means that your Linux
- * device structure does not match your HW device structure.
- * It would be best to refactor the Linux device structure to
- * correctly match the HW structure.
- */
- dev_warn(dev, "DMA channels sourced from device %s",
- dev_name(config->dma_dev));
- dev = config->dma_dev;
- }
- for_each_pcm_streams(i) {
- if (pcm->flags & SND_DMAENGINE_PCM_FLAG_HALF_DUPLEX)
- name = "rx-tx";
- else
- name = dmaengine_pcm_dma_channel_names[i];
- if (config && config->chan_names[i])
- name = config->chan_names[i];
- chan = dma_request_chan(dev, name);
- if (IS_ERR(chan)) {
- /*
- * Only report probe deferral errors, channels
- * might not be present for devices that
- * support only TX or only RX.
- */
- if (PTR_ERR(chan) == -EPROBE_DEFER)
- return -EPROBE_DEFER;
- pcm->chan[i] = NULL;
- } else {
- pcm->chan[i] = chan;
- }
- if (pcm->flags & SND_DMAENGINE_PCM_FLAG_HALF_DUPLEX)
- break;
- }
- if (pcm->flags & SND_DMAENGINE_PCM_FLAG_HALF_DUPLEX)
- pcm->chan[1] = pcm->chan[0];
- return 0;
- }
- static void dmaengine_pcm_release_chan(struct dmaengine_pcm *pcm)
- {
- unsigned int i;
- for_each_pcm_streams(i) {
- if (!pcm->chan[i])
- continue;
- dma_release_channel(pcm->chan[i]);
- if (pcm->flags & SND_DMAENGINE_PCM_FLAG_HALF_DUPLEX)
- break;
- }
- }
- /**
- * snd_dmaengine_pcm_register - Register a dmaengine based PCM device
- * @dev: The parent device for the PCM device
- * @config: Platform specific PCM configuration
- * @flags: Platform specific quirks
- */
- int snd_dmaengine_pcm_register(struct device *dev,
- const struct snd_dmaengine_pcm_config *config, unsigned int flags)
- {
- const struct snd_soc_component_driver *driver;
- struct dmaengine_pcm *pcm;
- int ret;
- pcm = kzalloc(sizeof(*pcm), GFP_KERNEL);
- if (!pcm)
- return -ENOMEM;
- #ifdef CONFIG_DEBUG_FS
- pcm->component.debugfs_prefix = "dma";
- #endif
- pcm->config = config;
- pcm->flags = flags;
- ret = dmaengine_pcm_request_chan_of(pcm, dev, config);
- if (ret)
- goto err_free_dma;
- if (config && config->process)
- driver = &dmaengine_pcm_component_process;
- else
- driver = &dmaengine_pcm_component;
- ret = snd_soc_component_initialize(&pcm->component, driver, dev);
- if (ret)
- goto err_free_dma;
- ret = snd_soc_add_component(&pcm->component, NULL, 0);
- if (ret)
- goto err_free_dma;
- return 0;
- err_free_dma:
- dmaengine_pcm_release_chan(pcm);
- kfree(pcm);
- return ret;
- }
- EXPORT_SYMBOL_GPL(snd_dmaengine_pcm_register);
- /**
- * snd_dmaengine_pcm_unregister - Removes a dmaengine based PCM device
- * @dev: Parent device the PCM was register with
- *
- * Removes a dmaengine based PCM device previously registered with
- * snd_dmaengine_pcm_register.
- */
- void snd_dmaengine_pcm_unregister(struct device *dev)
- {
- struct snd_soc_component *component;
- struct dmaengine_pcm *pcm;
- component = snd_soc_lookup_component(dev, SND_DMAENGINE_PCM_DRV_NAME);
- if (!component)
- return;
- pcm = soc_component_to_pcm(component);
- snd_soc_unregister_component_by_driver(dev, component->driver);
- dmaengine_pcm_release_chan(pcm);
- kfree(pcm);
- }
- EXPORT_SYMBOL_GPL(snd_dmaengine_pcm_unregister);
- MODULE_LICENSE("GPL");
复制代码 snd_dmaengine_pcm_register() 函数的执行过程如下:
- 动态分配一个 struct dmaengine_pcm 结构对象,并初始化其 config 和 flags 等字段,struct dmaengine_pcm 结构定义 (位于 include/sound/dmaengine_pcm.h) 如下:
- struct dmaengine_pcm {
- struct dma_chan *chan[SNDRV_PCM_STREAM_LAST + 1];
- const struct snd_dmaengine_pcm_config *config;
- struct snd_soc_component component;
- unsigned int flags;
- };
复制代码 这个结构有一个 struct snd_soc_component 结构成员;
- 为数据的发送和接收申请 DMA 通道,这个需要在设备树的设备节点定义中,指定发送和接收引用的 DMA 通道,像下面这样:
- i2s0_8ch: i2s@fe470000 {
- . . . . . .
- dmas = <&dmac0 0>, <&dmac0 1>;
- dma-names = "tx", "rx";
- . . . . . .
- };
复制代码
- 根据传入的 config 参数,选择 struct snd_soc_component_driver,dmaengine_pcm_component_process 和 dmaengine_pcm_component 仅有的区别是,前者多定义了一个 copy_user 操作;
- 初始化并添加 struct snd_soc_component 结构对象,有一个函数 (位于 include/sound/dmaengine_pcm.h) 可以通过 struct snd_soc_component 结构对象获得 struct dmaengine_pcm 结构对象:
- static inline struct dmaengine_pcm *soc_component_to_pcm(struct snd_soc_component *p)
- {
- return container_of(p, struct dmaengine_pcm, component);
- }
复制代码 通用 DMA 引擎驱动程序支持的操作由 struct snd_soc_component_driver 定义。在全局 component 链表中,相应的 struct snd_soc_component 由注册它的 dev 标识。
使用了通用 DMA 引擎驱动程序的 ASoC 机器驱动程序,示例 (位于 sound/soc/rockchip/rockchip_rt5645.c) 如下:- SND_SOC_DAILINK_DEFS(pcm,
- DAILINK_COMP_ARRAY(COMP_EMPTY()),
- DAILINK_COMP_ARRAY(COMP_CODEC(NULL, "rt5645-aif1")),
- DAILINK_COMP_ARRAY(COMP_EMPTY()));
- static struct snd_soc_dai_link rk_dailink = {
- .name = "rt5645",
- .stream_name = "rt5645 PCM",
- .init = rk_init,
- .ops = &rk_aif1_ops,
- /* set rt5645 as slave */
- .dai_fmt = SND_SOC_DAIFMT_I2S | SND_SOC_DAIFMT_NB_NF |
- SND_SOC_DAIFMT_CBS_CFS,
- SND_SOC_DAILINK_REG(pcm),
- };
- static struct snd_soc_card snd_soc_card_rk = {
- .name = "I2S-RT5650",
- .owner = THIS_MODULE,
- .dai_link = &rk_dailink,
- .num_links = 1,
- .dapm_widgets = rk_dapm_widgets,
- .num_dapm_widgets = ARRAY_SIZE(rk_dapm_widgets),
- .dapm_routes = rk_audio_map,
- .num_dapm_routes = ARRAY_SIZE(rk_audio_map),
- .controls = rk_mc_controls,
- .num_controls = ARRAY_SIZE(rk_mc_controls),
- };
- . . . . . .
- static int snd_rk_mc_probe(struct platform_device *pdev)
- {
- . . . . . .
- rk_dailink.cpus->of_node = of_parse_phandle(np,
- "rockchip,i2s-controller", 0);
- if (!rk_dailink.cpus->of_node) {
- dev_err(&pdev->dev,
- "Property 'rockchip,i2s-controller' missing or invalid\n");
- ret = -EINVAL;
- goto put_codec_of_node;
- }
- rk_dailink.platforms->of_node = rk_dailink.cpus->of_node;
- . . . . . .
- }
复制代码 这里为 dai link 定义的 cpus dai 数组和 platforms 数组中都只有一个空元素,但在 probe 操作中,根据设备树中设备节点的定义,查找了对应的 of_node。尽管 cpus dai 和 platforms 引用了相同的 of_node,但在 snd_soc_add_pcm_runtime() 函数中,为 CPU DAI 添加 struct snd_soc_component 的过程是,先查找对应的 struct snd_soc_dai,再从 struct snd_soc_dai 获得 struct snd_soc_component,这也就意味着,为 CPU DAI 查找 struct snd_soc_component 时,不会找到没有 struct snd_soc_dai 的通用 DMA 引擎的 struct snd_soc_component。为 platforms 添加 struct snd_soc_component 的过程,则是直接查找所有匹配的 struct snd_soc_component 并添加。
在为 PCM 创建 struct snd_soc_pcm_runtime 时,即在机器类驱动程序的 probe 操作中,如果为 snd_soc_dai_link 做了类似于这里的处理,使 CPU DAI 和 platform 指向相同的 of_node,且对应于 of_node 的设备驱动程序注册了通用 DMA 引擎驱动程序,通用 DMA 引擎的 struct snd_soc_component 将会包含在它的 component 链表中。
通用 DMA 引擎驱动程序的 struct snd_soc_component_driver 还有一个特别的地方是,指定了 probe_order 为 SND_SOC_COMP_ORDER_LATE,这使得它的 probe 和 init 操作,相对而言,执行的更晚,同时它在 snd_soc_card 中的位置也更靠后一点。如在 soc_probe_link_components() 函数 (位于 sound/soc/soc-core.c) 中:- static int soc_probe_component(struct snd_soc_card *card,
- struct snd_soc_component *component)
- {
- struct snd_soc_dapm_context *dapm =
- snd_soc_component_get_dapm(component);
- struct snd_soc_dai *dai;
- int probed = 0;
- int ret;
- if (!strcmp(component->name, "snd-soc-dummy"))
- return 0;
- if (component->card) {
- if (component->card != card) {
- dev_err(component->dev,
- "Trying to bind component to card "%s" but is already bound to card "%s"\n",
- card->name, component->card->name);
- return -ENODEV;
- }
- return 0;
- }
- ret = snd_soc_component_module_get_when_probe(component);
- if (ret < 0)
- return ret;
- component->card = card;
- soc_set_name_prefix(card, component);
- soc_init_component_debugfs(component);
- snd_soc_dapm_init(dapm, card, component);
- ret = snd_soc_dapm_new_controls(dapm,
- component->driver->dapm_widgets,
- component->driver->num_dapm_widgets);
- if (ret != 0) {
- dev_err(component->dev,
- "Failed to create new controls %d\n", ret);
- goto err_probe;
- }
- for_each_component_dais(component, dai) {
- ret = snd_soc_dapm_new_dai_widgets(dapm, dai);
- if (ret != 0) {
- dev_err(component->dev,
- "Failed to create DAI widgets %d\n", ret);
- goto err_probe;
- }
- }
- ret = snd_soc_component_probe(component);
- if (ret < 0) {
- dev_err(component->dev,
- "ASoC: failed to probe component %d\n", ret);
- goto err_probe;
- }
- WARN(dapm->idle_bias_off &&
- dapm->bias_level != SND_SOC_BIAS_OFF,
- "codec %s can not start from non-off bias with idle_bias_off==1\n",
- component->name);
- probed = 1;
- /*
- * machine specific init
- * see
- * snd_soc_component_set_aux()
- */
- ret = snd_soc_component_init(component);
- if (ret < 0)
- goto err_probe;
- ret = snd_soc_add_component_controls(component,
- component->driver->controls,
- component->driver->num_controls);
- if (ret < 0)
- goto err_probe;
- ret = snd_soc_dapm_add_routes(dapm,
- component->driver->dapm_routes,
- component->driver->num_dapm_routes);
- if (ret < 0) {
- if (card->disable_route_checks) {
- dev_info(card->dev,
- "%s: disable_route_checks set, ignoring errors on add_routes\n",
- __func__);
- } else {
- dev_err(card->dev,
- "%s: snd_soc_dapm_add_routes failed: %d\n",
- __func__, ret);
- goto err_probe;
- }
- }
- /* see for_each_card_components */
- list_add(&component->card_list, &card->component_dev_list);
- err_probe:
- if (ret < 0)
- soc_remove_component(component, probed);
- return ret;
- }
- . . . . . .
- static int soc_probe_link_components(struct snd_soc_card *card)
- {
- struct snd_soc_component *component;
- struct snd_soc_pcm_runtime *rtd;
- int i, ret, order;
- for_each_comp_order(order) {
- for_each_card_rtds(card, rtd) {
- for_each_rtd_components(rtd, i, component) {
- if (component->driver->probe_order != order)
- continue;
- ret = soc_probe_component(card, component);
- if (ret < 0)
- return ret;
- }
- }
- }
- return 0;
- }
复制代码 这里用到的 for_each_comp_order() 宏定义 (位于 include/sound/soc-component.h) 如下:- #define SND_SOC_COMP_ORDER_FIRST -2
- #define SND_SOC_COMP_ORDER_EARLY -1
- #define SND_SOC_COMP_ORDER_NORMAL 0
- #define SND_SOC_COMP_ORDER_LATE 1
- #define SND_SOC_COMP_ORDER_LAST 2
- #define for_each_comp_order(order) \
- for (order = SND_SOC_COMP_ORDER_FIRST; \
- order <= SND_SOC_COMP_ORDER_LAST; \
- order++)
复制代码 回到通用 DMA 引擎驱动程序的 pcm_construct 操作 dmaengine_pcm_new() 函数,这个函数定义 (位于 sound/soc/soc-generic-dmaengine-pcm.c) 如下:- static const struct snd_soc_component_driver dmaengine_pcm_component = {
- .name = SND_DMAENGINE_PCM_DRV_NAME,
- .probe_order = SND_SOC_COMP_ORDER_LATE,
- .open = dmaengine_pcm_open,
- .close = dmaengine_pcm_close,
- .hw_params = dmaengine_pcm_hw_params,
- .trigger = dmaengine_pcm_trigger,
- .pointer = dmaengine_pcm_pointer,
- .pcm_construct = dmaengine_pcm_new,
- };
- static const struct snd_soc_component_driver dmaengine_pcm_component_process = {
- .name = SND_DMAENGINE_PCM_DRV_NAME,
- .probe_order = SND_SOC_COMP_ORDER_LATE,
- .open = dmaengine_pcm_open,
- .close = dmaengine_pcm_close,
- .hw_params = dmaengine_pcm_hw_params,
- .trigger = dmaengine_pcm_trigger,
- .pointer = dmaengine_pcm_pointer,
- .copy_user = dmaengine_copy_user,
- .pcm_construct = dmaengine_pcm_new,
- };
复制代码 这个函数分别为播放和录制申请 DMA 通道,并分配 DMA buffer 用于用户空间应用程序、内核 ALSA/ASoc 框架和硬件设备之间的数据交换。snd_pcm_set_managed_buffer() 函数分配 DMA 缓冲区。snd_pcm_set_managed_buffer() 函数定义 (位于 sound/core/pcm_memory.c) 如下:- int snd_soc_pcm_component_new(struct snd_soc_pcm_runtime *rtd)
- {
- struct snd_soc_component *component;
- int ret;
- int i;
- for_each_rtd_components(rtd, i, component) {
- if (component->driver->pcm_construct) {
- ret = component->driver->pcm_construct(component, rtd);
- if (ret < 0)
- return soc_component_ret(component, ret);
- }
- }
- return 0;
- }
复制代码 open 操作 dmaengine_pcm_open() 函数完成数据传输之前的准备工作,这个函数定义如下:- static int dmaengine_pcm_new(struct snd_soc_component *component,
- struct snd_soc_pcm_runtime *rtd)
- {
- struct dmaengine_pcm *pcm = soc_component_to_pcm(component);
- const struct snd_dmaengine_pcm_config *config = pcm->config;
- struct device *dev = component->dev;
- struct snd_pcm_substream *substream;
- size_t prealloc_buffer_size;
- size_t max_buffer_size;
- unsigned int i;
- if (config && config->prealloc_buffer_size) {
- prealloc_buffer_size = config->prealloc_buffer_size;
- max_buffer_size = config->pcm_hardware->buffer_bytes_max;
- } else {
- prealloc_buffer_size = 512 * 1024;
- max_buffer_size = SIZE_MAX;
- }
- for_each_pcm_streams(i) {
- substream = rtd->pcm->streams[i].substream;
- if (!substream)
- continue;
- if (!pcm->chan[i] && config && config->chan_names[i])
- pcm->chan[i] = dma_request_slave_channel(dev,
- config->chan_names[i]);
- if (!pcm->chan[i] && (pcm->flags & SND_DMAENGINE_PCM_FLAG_COMPAT)) {
- pcm->chan[i] = dmaengine_pcm_compat_request_channel(
- component, rtd, substream);
- }
- if (!pcm->chan[i]) {
- dev_err(component->dev,
- "Missing dma channel for stream: %d\n", i);
- return -EINVAL;
- }
- snd_pcm_set_managed_buffer(substream,
- SNDRV_DMA_TYPE_DEV_IRAM,
- dmaengine_dma_dev(pcm, substream),
- prealloc_buffer_size,
- max_buffer_size);
- if (!dmaengine_pcm_can_report_residue(dev, pcm->chan[i]))
- pcm->flags |= SND_DMAENGINE_PCM_FLAG_NO_RESIDUE;
- if (rtd->pcm->streams[i].pcm->name[0] == '\0') {
- strscpy_pad(rtd->pcm->streams[i].pcm->name,
- rtd->pcm->streams[i].pcm->id,
- sizeof(rtd->pcm->streams[i].pcm->name));
- }
- }
- return 0;
- }
复制代码 这里调用 snd_soc_dai_get_dma_data() 函数获得类型为 struct snd_dmaengine_dai_dma_data 的 DMA 数据。这是通用 DMA 引擎驱动程序和 I2S 等 DAI 驱动程序的一个约定,即需要在 DAI 驱动程序的 probe 操作中设置 DMA 数据,类似于下面这样:- static void preallocate_pages(struct snd_pcm_substream *substream,
- int type, struct device *data,
- size_t size, size_t max, bool managed)
- {
- if (snd_BUG_ON(substream->dma_buffer.dev.type))
- return;
- substream->dma_buffer.dev.type = type;
- substream->dma_buffer.dev.dev = data;
- if (size > 0 && preallocate_dma && substream->number < maximum_substreams)
- preallocate_pcm_pages(substream, size);
- if (substream->dma_buffer.bytes > 0)
- substream->buffer_bytes_max = substream->dma_buffer.bytes;
- substream->dma_max = max;
- if (max > 0)
- preallocate_info_init(substream);
- if (managed)
- substream->managed_buffer_alloc = 1;
- }
- . . . . . .
- void snd_pcm_set_managed_buffer(struct snd_pcm_substream *substream, int type,
- struct device *data, size_t size, size_t max)
- {
- preallocate_pages(substream, type, data, size, max, true);
- }
- EXPORT_SYMBOL(snd_pcm_set_managed_buffer);
复制代码 dmaengine_pcm_open() 函数主要是为流设置了运行时硬件参数。
对于其它操作,暂时不做太多说明。
Done.
来源:https://www.cnblogs.com/wolfcs/p/17658297.html
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