22-ASoC平台驱动
17.5.3 ASoC平台驱动
首先，在ASoC平台驱动部分，同样存在着Codec驱动中的snd_soc_dai、snd_soc_dai_ops、snd_soc_ops这3个结构体的实例用于描述DAI和DAI上的操作，不过不同的是，在平台驱动中，它们只描述CPU相关的部分而不描述Codec。除此之外，在ASoC平台驱动中，必须实现完整的DMA驱动，即传统ALSA的snd_pcm_ops结构体成员函数trigger()、pointer()等。因此ASoC平台驱动通常由DAI和DMA两部分组成，如代码清单17.32所示。
代码清单17.32 ASoC平台驱动的组成
1 / DAI部分 /
2 static int xxx_i2s_set_dai_fmt(struct snd_soc_dai *cpu_dai,
3 unsigned int fmt)
4 {
5 ...
6 }
7
8 static int xxx_i2s_startup(struct snd_pcm_substream *substream)
9 {
10 ...
11 }
12
13 static int xxx_i2s_hw_params(struct snd_pcm_substream *substream,
14 struct snd_pcm_hw_params *params)
15 {
16 ...
17 }
18
19 static void xxx_i2s_shutdown(struct snd_pcm_substream *substream)
20 {
21 ...
22 }
23
24 static int xxx_i2s_probe(struct platform_device *pdev,
25 struct snd_soc_dai *dai)
26 {
27 ...
28 }
29
30 static void xxx_i2s_remove(struct platform_device *pdev,
31 struct snd_soc_dai *dai)
32 {
33 ...
34 }
35
36 static int xxx_i2s_suspend(struct platform_device *dev,
37 struct snd_soc_dai *dai)
38 {
39 ...
40 }
41
42 static int xxx_i2s_resume(struct platform_device *pdev,
43 struct snd_soc_dai *dai)
44 {
45 ...
46 }
47
48 struct snd_soc_dai xxx_i2s_dai = {
49 .name = "xxx-i2s",
50 .id = 0,
51 .type = SND_SOC_DAI_I2S,
52 .probe = xxx_i2s_probe,
53 .remove = xxx_i2s_remove,
54 .suspend = xxx_i2s_suspend,
55 .resume = xxx_i2s_resume,
56 .playback = {
57 .channels_min = 1,
58 .channels_max = 2,
59 .rates = XXX_I2S_RATES,
60 .formats = XXX_I2S_FORMATS,},
61 .capture = {
62 .channels_min = 1,
63 .channels_max = 2,
64 .rates = XXX_I2S_RATES,
65 .formats = XXX_I2S_FORMATS,},
66 .ops = {
67 .startup = xxx_i2s_startup,
68 .shutdown = xxx_i2s_shutdown,
69 .hw_params = xxx_i2s_hw_params,},
70 .dai_ops = {
71 .set_fmt = xxx_i2s_set_dai_fmt,
72 },
73 };
74
75 / DMA部分 /
76 static void bf5xx_dma_irq(void *data)
77 {
78 struct snd_pcm_substream *pcm = data;
79 snd_pcm_period_elapsed(pcm);
80 }
81
82 static const struct snd_pcm_hardware xxx_pcm_hardware = {
83 ...
84 };
85
86 static int xxx_pcm_hw_params(struct snd_pcm_substream *substream,
87 struct snd_pcm_hw_params *params)
88 {
89 ...
90 snd_pcm_lib_malloc_pages(substream, size);
91
92 return 0;
93 }
94
95 static int xxx_pcm_hw_free(struct snd_pcm_substream *substream)
96 {
97 snd_pcm_lib_free_pages(substream);
98
99 return 0;
100 }
101
102 static int xxx_pcm_prepare(struct snd_pcm_substream *substream)
103 {
104 ...
105 }
106
107 static int xxx_pcm_trigger(struct snd_pcm_substream *substream, int cmd)
108 {
109 ...
110 }
111
112 static snd_pcm_uframes_t xxx_pcm_pointer(struct snd_pcm_substream *substream)
113 {
114 ...
115 }
116
117 static int xxx_pcm_open(struct snd_pcm_substream *substream)
118 {
119 ...
120 }
121
122 static int xxx_pcm_mmap(struct snd_pcm_substream *substream,
123 struct vm_area_struct *vma)
124 {
125 ...;
126 }
127
128 struct snd_pcm_ops xxx_pcm_i2s_ops = {
129 .open = xxx_pcm_open,
130 .ioctl = snd_pcm_lib_ioctl,
131 .hw_params = xxx_pcm_hw_params,
132 .hw_free = xxx_pcm_hw_free,
133 .prepare = xxx_pcm_prepare,
134 .trigger = xxx_pcm_trigger,
135 .pointer = xxx_pcm_pointer,
136 .mmap = xxx_pcm_mmap,
137 };