[PATCH 02/11] dmaengine: stm32-dma3: prevent pack/unpack thanks to DT configuration

Amelie Delaunay
2024-10-10T14:31:46Z

When source data width/burst and destination data width/burst are
different, data are packed or unpacked in DMA3 channel FIFO, using
CxTR1.PAM.
Data are pushed out from DMA3 channel FIFO when the destination burst
length (= data width * burst) is reached.
If the transfer is stopped before CxBR1.BNDT = 0, and if some bytes are
packed/unpacked in the DMA3 channel FIFO, these bytes are lost.
Indeed, DMA3 channel FIFO has no flush capability, only reset.
To avoid potential bytes lost, pack/unpack must be prevented by setting
memory data width/burst equal to peripheral data width/burst.
Memory accesses will be penalized. But it is the only way to avoid bytes
lost.

Prevent pack/unpack feature can be activated by setting bit 16 of DMA3
Transfer requirements bitfield (tr_conf) in device tree.

Signed-off-by: Amelie Delaunay <amelie.delaunay@foss.st.com>
---
drivers/dma/stm32/stm32-dma3.c | 10 ++++++++++
1 file changed, 10 insertions(+)

diff --git a/drivers/dma/stm32/stm32-dma3.c b/drivers/dma/stm32/stm32-dma3.c
index 0be6e944df6fd5d2a02974085251549d9389a37e..2b4cc479e1a1206fef7fd2808d1342048d81e07b 100644
--- a/drivers/dma/stm32/stm32-dma3.c
+++ b/drivers/dma/stm32/stm32-dma3.c
@@ -221,6 +221,7 @@ enum stm32_dma3_port_data_width {
#define STM32_DMA3_DT_BREQ BIT(8) /* CTR2_BREQ */
#define STM32_DMA3_DT_PFREQ BIT(9) /* CTR2_PFREQ */
#define STM32_DMA3_DT_TCEM GENMASK(13, 12) /* CTR2_TCEM */
+#define STM32_DMA3_DT_NOPACK BIT(16) /* CTR1_PAM */

/* struct stm32_dma3_chan .config_set bitfield */
#define STM32_DMA3_CFG_SET_DT BIT(0)
@@ -622,6 +623,10 @@ static int stm32_dma3_chan_prep_hw(struct stm32_dma3_chan *chan, enum dma_transf
/* Set source (memory) data width and burst */
sdw = stm32_dma3_get_max_dw(chan->max_burst, sap_max_dw, len, src_addr);
sbl_max = stm32_dma3_get_max_burst(len, sdw, chan->max_burst);
+ if (!!FIELD_GET(STM32_DMA3_DT_NOPACK, tr_conf)) {
+ sdw = ddw;
+ sbl_max = dbl_max;
+ }

_ctr1 |= FIELD_PREP(CTR1_SDW_LOG2, ilog2(sdw));
_ctr1 |= FIELD_PREP(CTR1_SBL_1, sbl_max - 1);
@@ -652,6 +657,11 @@ static int stm32_dma3_chan_prep_hw(struct stm32_dma3_chan *chan, enum dma_transf
/* Set destination (memory) data width and burst */
ddw = stm32_dma3_get_max_dw(chan->max_burst, dap_max_dw, len, dst_addr);
dbl_max = stm32_dma3_get_max_burst(len, ddw, chan->max_burst);
+ if (!!FIELD_GET(STM32_DMA3_DT_NOPACK, tr_conf) ||
+ ((_ctr2 & CTR2_PFREQ) && ddw > sdw)) { /* Packing to wider ddw not supported */
+ ddw = sdw;
+ dbl_max = sbl_max;
+ }

_ctr1 |= FIELD_PREP(CTR1_SDW_LOG2, ilog2(sdw));
_ctr1 |= FIELD_PREP(CTR1_SBL_1, sbl_max - 1);

--
2.25.1