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>

1 files changed, 13 insertions, 8 deletions

diff --git a/sound/soc/stm/stm32_sai_sub.c b/sound/soc/stm/stm32_sai_sub.c
index 5e66bf310351..dde8ddf9e777 100644
--- 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;