ASoC: stm32: sai: Fix DMA burst size

Set best burst size tradeoff for 8, 16, 32 bits transfers.

Signed-off-by: olivier moysan <olivier.moysan@st.com>
Signed-off-by: Mark Brown <broonie@kernel.org>

diff --git a/sound/soc/stm/stm32_sai_sub.c b/sound/soc/stm/stm32_sai_sub.c
index 5e66bf310351bf59be1aead622228206c7fad919..dde8ddf9e777b04e5d23850f42f51150a26f6278 100644 (file)
--- a/sound/soc/stm/stm32_sai_sub.c
+++ b/sound/soc/stm/stm32_sai_sub.c
@@ -446,12 +446,16 @@ static int stm32_sai_set_config(struct snd_soc_dai *cpu_dai,
 {
        struct stm32_sai_sub_data *sai = snd_soc_dai_get_drvdata(cpu_dai);
        int cr1, cr1_mask, ret;
-       int fth = STM_SAI_FIFO_TH_HALF;
 
-       /* FIFO config */
+       /*
+        * DMA bursts increment is set to 4 words.
+        * SAI fifo threshold is set to half fifo, to keep enough space
+        * for DMA incoming bursts.
+        */
        regmap_update_bits(sai->regmap, STM_SAI_CR2_REGX,
                           SAI_XCR2_FFLUSH | SAI_XCR2_FTH_MASK,
-                          SAI_XCR2_FFLUSH | SAI_XCR2_FTH_SET(fth));
+                          SAI_XCR2_FFLUSH |
+                          SAI_XCR2_FTH_SET(STM_SAI_FIFO_TH_HALF));
 
        /* Mode, data format and channel config */
        cr1 = SAI_XCR1_PRTCFG_SET(SAI_FREE_PROTOCOL);
@@ -485,10 +489,6 @@ static int stm32_sai_set_config(struct snd_soc_dai *cpu_dai,
                return ret;
        }
 
-       /* DMA config */
-       sai->dma_params.maxburst = STM_SAI_FIFO_SIZE * fth / sizeof(u32);
-       snd_soc_dai_set_dma_data(cpu_dai, substream, (void *)&sai->dma_params);
-
        return 0;
 }
 
@@ -731,7 +731,12 @@ static int stm32_sai_dai_probe(struct snd_soc_dai *cpu_dai)
        struct stm32_sai_sub_data *sai = dev_get_drvdata(cpu_dai->dev);
 
        sai->dma_params.addr = (dma_addr_t)(sai->phys_addr + STM_SAI_DR_REGX);
-       sai->dma_params.maxburst = 1;
+       /*
+        * DMA supports 4, 8 or 16 burst sizes. Burst size 4 is the best choice,
+        * as it allows bytes, half-word and words transfers. (See DMA fifos
+        * constraints).
+        */
+       sai->dma_params.maxburst = 4;
        /* Buswidth will be set by framework at runtime */
        sai->dma_params.addr_width = DMA_SLAVE_BUSWIDTH_UNDEFINED;