ASoC: atmel: mchp-pdmc: Improve maxburst calculation for better performance

Improve the DMA descriptor calculation by dividing the period size by the
product of sample size and DMA chunk size, rather than just DMA chunk size.
Ensure that all DMA descriptors start from a well-aligned address to
improve the reliability and efficiency of DMA operations and avoid
potential issues related to misaligned descriptors.

[andrei.simion@microchip.com: Adjust the commit title. Reword the commit
message. Add MACROS for each DMA size chunk supported by mchp-pdmc.
Add DMA_BURST_ALIGNED preprocesor function to check the alignment of the
DMA burst.]

Signed-off-by: Codrin Ciubotariu <codrin.ciubotariu@microchip.com>
Signed-off-by: Andrei Simion <andrei.simion@microchip.com>
Link: https://patch.msgid.link/20240911122909.133399-2-andrei.simion@microchip.com
Signed-off-by: Mark Brown <broonie@kernel.org>

Author: Codrin Ciubotariu

sound/soc/atmel/mchp-pdmc.c

@@ -90,6 +90,15 @@
 #define MCHP_PDMC_DS_NO			2
 #define MCHP_PDMC_EDGE_NO		2
 
+/*
+ * ---- DMA chunk size allowed ----
+ */
+#define MCHP_PDMC_DMA_8_WORD_CHUNK			8
+#define MCHP_PDMC_DMA_4_WORD_CHUNK			4
+#define MCHP_PDMC_DMA_2_WORD_CHUNK			2
+#define MCHP_PDMC_DMA_1_WORD_CHUNK			1
+#define DMA_BURST_ALIGNED(_p, _s, _w)		!(_p % (_s * _w))
+
 struct mic_map {
 	int ds_pos;
 	int clk_edge;
@@ -511,15 +520,18 @@ static u32 mchp_pdmc_mr_set_osr(int audio_filter_en, unsigned int osr)
 	return 0;
 }
 
-static inline int mchp_pdmc_period_to_maxburst(int period_size)
+static inline int mchp_pdmc_period_to_maxburst(int period_size, int sample_size)
 {
-	if (!(period_size % 8))
-		return 8;
-	if (!(period_size % 4))
-		return 4;
-	if (!(period_size % 2))
-		return 2;
-	return 1;
+	int p_size = period_size;
+	int s_size = sample_size;
+
+	if (DMA_BURST_ALIGNED(p_size, s_size, MCHP_PDMC_DMA_8_WORD_CHUNK))
+		return MCHP_PDMC_DMA_8_WORD_CHUNK;
+	if (DMA_BURST_ALIGNED(p_size, s_size, MCHP_PDMC_DMA_4_WORD_CHUNK))
+		return MCHP_PDMC_DMA_4_WORD_CHUNK;
+	if (DMA_BURST_ALIGNED(p_size, s_size, MCHP_PDMC_DMA_2_WORD_CHUNK))
+		return MCHP_PDMC_DMA_2_WORD_CHUNK;
+	return MCHP_PDMC_DMA_1_WORD_CHUNK;
 }
 
 static struct snd_pcm_chmap_elem mchp_pdmc_std_chmaps[] = {
@@ -547,14 +559,18 @@ static int mchp_pdmc_hw_params(struct snd_pcm_substream *substream,
 	unsigned int channels = params_channels(params);
 	unsigned int osr = 0, osr_start;
 	unsigned int fs = params_rate(params);
+	int sample_bytes = params_physical_width(params) / 8;
+	int period_bytes = params_period_size(params) *
+		params_channels(params) * sample_bytes;
+	int maxburst;
 	u32 mr_val = 0;
 	u32 cfgr_val = 0;
 	int i;
 	int ret;
 
-	dev_dbg(comp->dev, "%s() rate=%u format=%#x width=%u channels=%u\n",
+	dev_dbg(comp->dev, "%s() rate=%u format=%#x width=%u channels=%u period_bytes=%d\n",
 		__func__, params_rate(params), params_format(params),
-		params_width(params), params_channels(params));
+		params_width(params), params_channels(params), period_bytes);
 
 	if (channels > dd->mic_no) {
 		dev_err(comp->dev, "more channels %u than microphones %d\n",
@@ -608,7 +624,8 @@ static int mchp_pdmc_hw_params(struct snd_pcm_substream *substream,
 
 	mr_val |= FIELD_PREP(MCHP_PDMC_MR_SINCORDER_MASK, dd->sinc_order);
 
-	dd->addr.maxburst = mchp_pdmc_period_to_maxburst(snd_pcm_lib_period_bytes(substream));
+	maxburst = mchp_pdmc_period_to_maxburst(period_bytes, sample_bytes);
+	dd->addr.maxburst = maxburst;
 	mr_val |= FIELD_PREP(MCHP_PDMC_MR_CHUNK_MASK, dd->addr.maxburst);
 	dev_dbg(comp->dev, "maxburst set to %d\n", dd->addr.maxburst);