// SPDX-License-Identifier: GPL-2.0-only #include <linux/module.h> #include <linux/of.h> #include <linux/platform_device.h> #include <sound/soc.h> /* * The I2S interface consists of two ring buffers - one for RX and one for * TX. A ring buffer has a producer index and a consumer index. Depending * on which way the data is flowing, either the software or the hardware * writes data and updates the producer index, and the other end reads data * and updates the consumer index. * * The pointer managed by software is updated using the .ack callback * (see chv3_dma_ack). This seems to be the only way to reliably obtain * the appl_ptr from within the driver and pass it to hardware. * * Because of the two pointer design, the ring buffer can never be full. With * capture this isn't a problem, because the hardware being the producer * will wait for the consumer index to move out of the way. With playback, * however, this is problematic, because ALSA wants to fill up the buffer * completely when waiting for hardware. In the .ack callback, the driver * would have to wait for the consumer index to move out of the way by * busy-waiting, which would keep stalling the kernel for quite a long time. * * The workaround to this problem is to "lie" to ALSA that the hw_pointer * is one frame behind what it actually is (see chv3_dma_pointer). This * way, ALSA will not try to fill up the entire buffer, and all callbacks * are wait-free. */ #define I2S_TX_ENABLE … #define I2S_TX_BASE_ADDR … #define I2S_TX_BUFFER_SIZE … #define I2S_TX_PRODUCER_IDX … #define I2S_TX_CONSUMER_IDX … #define I2S_RX_ENABLE … #define I2S_RX_BASE_ADDR … #define I2S_RX_BUFFER_SIZE … #define I2S_RX_PRODUCER_IDX … #define I2S_RX_CONSUMER_IDX … #define I2S_SOFT_RESET … #define I2S_SOFT_RESET_RX_BIT … #define I2S_SOFT_RESET_TX_BIT … #define I2S_RX_IRQ … #define I2S_RX_IRQ_CONST … #define I2S_TX_IRQ … #define I2S_TX_IRQ_CONST … #define I2S_IRQ_MASK … #define I2S_IRQ_CLR … #define I2S_IRQ_RX_BIT … #define I2S_IRQ_TX_BIT … #define I2S_MAX_BUFFER_SIZE … struct chv3_i2s_dev { … }; static struct snd_soc_dai_driver chv3_i2s_dai = …; static const struct snd_pcm_hardware chv3_dma_hw = …; static inline void chv3_i2s_wr(struct chv3_i2s_dev *i2s, int offset, u32 val) { … } static inline u32 chv3_i2s_rd(struct chv3_i2s_dev *i2s, int offset) { … } static irqreturn_t chv3_i2s_isr(int irq, void *data) { … } static int chv3_dma_open(struct snd_soc_component *component, struct snd_pcm_substream *substream) { … } static int chv3_dma_close(struct snd_soc_component *component, struct snd_pcm_substream *substream) { … } static int chv3_dma_pcm_construct(struct snd_soc_component *component, struct snd_soc_pcm_runtime *rtd) { … } static int chv3_dma_hw_params(struct snd_soc_component *component, struct snd_pcm_substream *substream, struct snd_pcm_hw_params *params) { … } static int chv3_dma_prepare(struct snd_soc_component *component, struct snd_pcm_substream *substream) { … } static snd_pcm_uframes_t chv3_dma_pointer(struct snd_soc_component *component, struct snd_pcm_substream *substream) { … } static int chv3_dma_ack(struct snd_soc_component *component, struct snd_pcm_substream *substream) { … } static const struct snd_soc_component_driver chv3_i2s_comp = …; static int chv3_i2s_probe(struct platform_device *pdev) { … } static const struct of_device_id chv3_i2s_of_match[] = …; static struct platform_driver chv3_i2s_driver = …; module_platform_driver(…) …; MODULE_AUTHOR(…) …; MODULE_DESCRIPTION(…) …; MODULE_LICENSE(…) …;
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