ALSA在Linux3.1上的一些改进
ALSA在Linux3.1上的一些改进
Android迈进了4.0,相应的Linux内核也进入了3.x时代。之后的一个工作估计要将2.6.32的驱动移植到3.x上面来。因此趁现在有空,看看alsa在这方面有什么改动。
总的来说,架构大的改动是不大可能的。codec中几个关键结构体没有大的变化,如snd_soc_dai_ops、snd_soc_dai_driver(相当于2.6.32中的snd_soc_dai),倒是以前的snd_soc_codec_device重定义为snd_soc_codec_driver,这个算是最明显的。
注册用结构体-snd_soc_codec_driver
2.6.32:
[cpp]- /* codec device */
- struct snd_soc_codec_device {
- int (*probe)(struct platform_device *pdev);
- int (*remove)(struct platform_device *pdev);
- int (*suspend)(struct platform_device *pdev, pm_message_t state);
- int (*resume)(struct platform_device *pdev);
- };
- /* codec driver */
- struct snd_soc_codec_driver {
- /* driver ops */
- int (*probe)(struct snd_soc_codec *);
- int (*remove)(struct snd_soc_codec *);
- int (*suspend)(struct snd_soc_codec *,
- pm_message_t state);
- int (*resume)(struct snd_soc_codec *);
- /* Default control and setup, added after probe() is run */
- const struct snd_kcontrol_new *controls;
- int num_controls;
- const struct snd_soc_dapm_widget *dapm_widgets;
- int num_dapm_widgets;
- const struct snd_soc_dapm_route *dapm_routes;
- int num_dapm_routes;
- /* codec wide operations */
- int (*set_sysclk)(struct snd_soc_codec *codec,
- int clk_id, unsigned int freq, int dir);
- int (*set_pll)(struct snd_soc_codec *codec, int pll_id, int source,
- unsigned int freq_in, unsigned int freq_out);
- /* codec IO */
- unsigned int (*read)(struct snd_soc_codec *, unsigned int);
- int (*write)(struct snd_soc_codec *, unsigned int, unsigned int);
- int (*display_register)(struct snd_soc_codec *, char *,
- size_t, unsigned int);
- int (*volatile_register)(struct snd_soc_codec *, unsigned int);
- int (*readable_register)(struct snd_soc_codec *, unsigned int);
- int (*writable_register)(struct snd_soc_codec *, unsigned int);
- short reg_cache_size;
- short reg_cache_step;
- short reg_word_size;
- const void *reg_cache_default;
- short reg_access_size;
- const struct snd_soc_reg_access *reg_access_default;
- enum snd_soc_compress_type compress_type;
- /* codec bias level */
- int (*set_bias_level)(struct snd_soc_codec *,
- enum snd_soc_bias_level level);
- void (*seq_notifier)(struct snd_soc_dapm_context *,
- enum snd_soc_dapm_type, int);
- /* probe ordering - for components with runtime dependencies */
- int probe_order;
- int remove_order;
- };
位于snd_soc_codec_driver中的一些codec IO成员函数和set_bias_level回调函数原来都放在另外一个结构体snd_soc_codec中,现在放置在这里了,这是根据源码结构调整的结果。事实真正需要设置的成员也不是很多,如下:
[cpp]- static struct snd_soc_codec_driver soc_codec_dev_wm9713 = {
- .probe = wm9713_soc_probe,
- .remove = wm9713_soc_remove,
- .suspend = wm9713_soc_suspend,
- .resume = wm9713_soc_resume,
- .read = ac97_read,
- .write = ac97_write,
- .set_bias_level = wm9713_set_bias_level,
- .reg_cache_size = ARRAY_SIZE(wm9713_reg),
- .reg_word_size = sizeof(u16),
- .reg_cache_step = 2,
- .reg_cache_default = wm9713_reg,
- .dapm_widgets = wm9713_dapm_widgets,
- .num_dapm_widgets = ARRAY_SIZE(wm9713_dapm_widgets),
- .dapm_routes = wm9713_audio_map,
- .num_dapm_routes = ARRAY_SIZE(wm9713_audio_map),
- };
probe、remove、suspend、resume相信不用累述了,volatile_register函数判断指定的寄存器是否volatile,reg_cache_size一般为寄存器数目,reg_word_size为寄存器的字长,reg_cache_default为寄存器默认值配置表。
而dapm_widgets、dapm_routes就比较“犀利”了。之前的dapm widgets和routes分别通过函数snd_soc_dapm_new_controls和snd_soc_dapm_add_routes来注册的(当然现在还保留这些接口),现在则可以填入到这个结构体,在soc-core里注册,省了不少功夫:
[cpp]- static int soc_probe_codec(struct snd_soc_card *card,
- struct snd_soc_codec *codec)
- {
- //...
- if (driver->dapm_widgets)
- snd_soc_dapm_new_controls(&codec->dapm, driver->dapm_widgets,
- driver->num_dapm_widgets);
- //...
- if (driver->controls)
- snd_soc_add_controls(codec, driver->controls,
- driver->num_controls);
- if (driver->dapm_routes)
- snd_soc_dapm_add_routes(&codec->dapm, driver->dapm_routes,
- driver->num_dapm_routes);
- //...
- }
同时可看到dirver ops的函数参数有所不同了,以前是struct platform_device *pdev,现在改为struct snd_soc_codec *codec,这个与codec的注册函数snd_soc_register_codec和设备的drvdata有关,之后会逐一分析。
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