STM32 DMA3 can be interconnected with AXI3 or AXI4 busses. In case it is
interconnected with AXI3, the maximum burst length supported by AXI3
protocol is 16 beats, which is lower than the maximum burst length
supported by STM32 DMA3. So the programmed burst has to be shortened when
AXI port is used.

Signed-off-by: Amelie Delaunay <amelie.delaunay@foss.st.com>
---
 drivers/dma/stm32/stm32-dma3.c | 47 +++++++++++++++++++++++++++++++-----------
 1 file changed, 35 insertions(+), 12 deletions(-)

diff --git a/drivers/dma/stm32/stm32-dma3.c b/drivers/dma/stm32/stm32-dma3.c
index 1467308dd27c4674b13d2740c05087b1338fd91a..e10689038d8269d23c3f38af9b19cad0b6761fe3 100644
--- a/drivers/dma/stm32/stm32-dma3.c
+++ b/drivers/dma/stm32/stm32-dma3.c
@@ -230,6 +230,8 @@ enum stm32_dma3_port_data_width {
 #define STM32_DMA3_CFG_SET_BOTH		(STM32_DMA3_CFG_SET_DT | STM32_DMA3_CFG_SET_DMA)
 
 #define STM32_DMA3_MAX_BLOCK_SIZE	ALIGN_DOWN(CBR1_BNDT, 64)
+#define STM32_DMA3_MAX_BURST_LEN	(1 + min_t(u32, FIELD_GET(CTR1_SBL_1, CTR1_SBL_1), \
+							FIELD_GET(CTR1_DBL_1, CTR1_DBL_1)))
 #define port_is_ahb(maxdw)		({ typeof(maxdw) (_maxdw) = (maxdw); \
 					   ((_maxdw) != DW_INVALID) && ((_maxdw) == DW_32); })
 #define port_is_axi(maxdw)		({ typeof(maxdw) (_maxdw) = (maxdw); \
@@ -303,6 +305,7 @@ struct stm32_dma3_ddata {
 	u32 dma_channels;
 	u32 dma_requests;
 	enum stm32_dma3_port_data_width ports_max_dw[2];
+	u32 axi_max_burst_len;
 };
 
 static inline struct stm32_dma3_ddata *to_stm32_dma3_ddata(struct stm32_dma3_chan *chan)
@@ -535,7 +538,8 @@ static enum dma_slave_buswidth stm32_dma3_get_max_dw(u32 chan_max_burst,
 	return 1 << __ffs(len | addr | max_dw);
 }
 
-static u32 stm32_dma3_get_max_burst(u32 len, enum dma_slave_buswidth dw, u32 chan_max_burst)
+static u32 stm32_dma3_get_max_burst(u32 len, enum dma_slave_buswidth dw,
+				    u32 chan_max_burst, u32 bus_max_burst)
 {
 	u32 max_burst = chan_max_burst ? chan_max_burst / dw : 1;
 
@@ -546,8 +550,9 @@ static u32 stm32_dma3_get_max_burst(u32 len, enum dma_slave_buswidth dw, u32 cha
 	/*
 	 * HW doesn't modify the burst if burst size <= half of the fifo size.
 	 * If len is not a multiple of burst size, last burst is shortened by HW.
+	 * Take care of maximum burst supported on interconnect bus.
 	 */
-	return max_burst;
+	return min_t(u32, max_burst, bus_max_burst);
 }
 
 static int stm32_dma3_chan_prep_hw(struct stm32_dma3_chan *chan, enum dma_transfer_direction dir,
@@ -556,6 +561,7 @@ static int stm32_dma3_chan_prep_hw(struct stm32_dma3_chan *chan, enum dma_transf
 {
 	struct stm32_dma3_ddata *ddata = to_stm32_dma3_ddata(chan);
 	struct dma_device dma_device = ddata->dma_dev;
+	u32 src_max_burst = STM32_DMA3_MAX_BURST_LEN, dst_max_burst = STM32_DMA3_MAX_BURST_LEN;
 	u32 sdw, ddw, sbl_max, dbl_max, tcem, init_dw, init_bl_max;
 	u32 _ctr1 = 0, _ctr2 = 0;
 	u32 ch_conf = chan->dt_config.ch_conf;
@@ -596,10 +602,14 @@ static int stm32_dma3_chan_prep_hw(struct stm32_dma3_chan *chan, enum dma_transf
 		_ctr1 |= CTR1_SINC;
 	if (sap)
 		_ctr1 |= CTR1_SAP;
+	if (port_is_axi(sap_max_dw)) /* AXI - apply axi maximum burst limitation */
+		src_max_burst = ddata->axi_max_burst_len;
 	if (FIELD_GET(STM32_DMA3_DT_DINC, tr_conf))
 		_ctr1 |= CTR1_DINC;
 	if (dap)
 		_ctr1 |= CTR1_DAP;
+	if (port_is_axi(dap_max_dw)) /* AXI - apply axi maximum burst limitation */
+		dst_max_burst = ddata->axi_max_burst_len;
 
 	_ctr2 |= FIELD_PREP(CTR2_REQSEL, chan->dt_config.req_line) & ~CTR2_SWREQ;
 	if (FIELD_GET(STM32_DMA3_DT_BREQ, tr_conf))
@@ -619,11 +629,12 @@ static int stm32_dma3_chan_prep_hw(struct stm32_dma3_chan *chan, enum dma_transf
 		/* Set destination (device) data width and burst */
 		ddw = min_t(u32, ddw, stm32_dma3_get_max_dw(chan->max_burst, dap_max_dw,
 							    len, dst_addr));
-		dbl_max = min_t(u32, dbl_max, stm32_dma3_get_max_burst(len, ddw, chan->max_burst));
+		dbl_max = min_t(u32, dbl_max, stm32_dma3_get_max_burst(len, ddw, chan->max_burst,
+								       dst_max_burst));
 
 		/* 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);
+		sbl_max = stm32_dma3_get_max_burst(len, sdw, chan->max_burst, src_max_burst);
 		if (!!FIELD_GET(STM32_DMA3_DT_NOPACK, tr_conf)) {
 			sdw = ddw;
 			sbl_max = dbl_max;
@@ -653,11 +664,12 @@ static int stm32_dma3_chan_prep_hw(struct stm32_dma3_chan *chan, enum dma_transf
 		/* Set source (device) data width and burst */
 		sdw = min_t(u32, sdw, stm32_dma3_get_max_dw(chan->max_burst, sap_max_dw,
 							    len, src_addr));
-		sbl_max = min_t(u32, sbl_max, stm32_dma3_get_max_burst(len, sdw, chan->max_burst));
+		sbl_max = min_t(u32, sbl_max, stm32_dma3_get_max_burst(len, sdw, chan->max_burst,
+								       src_max_burst));
 
 		/* 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);
+		dbl_max = stm32_dma3_get_max_burst(len, ddw, chan->max_burst, dst_max_burst);
 		if (!!FIELD_GET(STM32_DMA3_DT_NOPACK, tr_conf) ||
 		    ((_ctr2 & CTR2_PFREQ) && ddw > sdw)) { /* Packing to wider ddw not supported */
 			ddw = sdw;
@@ -689,22 +701,24 @@ static int stm32_dma3_chan_prep_hw(struct stm32_dma3_chan *chan, enum dma_transf
 		init_dw = sdw;
 		init_bl_max = sbl_max;
 		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);
+		sbl_max = stm32_dma3_get_max_burst(len, sdw, chan->max_burst, src_max_burst);
 		if (chan->config_set & STM32_DMA3_CFG_SET_DMA) {
 			sdw = min_t(u32, init_dw, sdw);
-			sbl_max = min_t(u32, init_bl_max,
-					stm32_dma3_get_max_burst(len, sdw, chan->max_burst));
+			sbl_max = min_t(u32, init_bl_max, stm32_dma3_get_max_burst(len, sdw,
+										   chan->max_burst,
+										   src_max_burst));
 		}
 
 		/* Set destination (memory) data width and burst */
 		init_dw = ddw;
 		init_bl_max = dbl_max;
 		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);
+		dbl_max = stm32_dma3_get_max_burst(len, ddw, chan->max_burst, dst_max_burst);
 		if (chan->config_set & STM32_DMA3_CFG_SET_DMA) {
 			ddw = min_t(u32, init_dw, ddw);
-			dbl_max = min_t(u32, init_bl_max,
-					stm32_dma3_get_max_burst(len, ddw, chan->max_burst));
+			dbl_max = min_t(u32, init_bl_max, stm32_dma3_get_max_burst(len, ddw,
+										   chan->max_burst,
+										   dst_max_burst));
 		}
 
 		_ctr1 |= FIELD_PREP(CTR1_SDW_LOG2, ilog2(sdw));
@@ -1750,6 +1764,15 @@ static int stm32_dma3_probe(struct platform_device *pdev)
 	else /* Dual master ports */
 		ddata->ports_max_dw[1] = FIELD_GET(G_M1_DATA_WIDTH_ENC, hwcfgr);
 
+	/* st,axi-max-burst-len is optional, if not defined, use STM32_DMA3_MAX_BURST_LEN  */
+	if (of_property_read_u32(np, "st,axi-max-burst-len", &ddata->axi_max_burst_len))
+		ddata->axi_max_burst_len = STM32_DMA3_MAX_BURST_LEN;
+	else
+		ddata->axi_max_burst_len = min_t(u32, ddata->axi_max_burst_len,
+						 STM32_DMA3_MAX_BURST_LEN);
+	dev_dbg(&pdev->dev, "Burst is limited to %u beats through AXI port\n",
+		ddata->axi_max_burst_len);
+
 	ddata->chans = devm_kcalloc(&pdev->dev, ddata->dma_channels, sizeof(*ddata->chans),
 				    GFP_KERNEL);
 	if (!ddata->chans) {

-- 
2.25.1