dmaengine: dw-axi-dmac: Per-channel burst limits

The DesignWare AXI DMAC IP can be configured with heterogeneous channel
parameters. Allow maximum burst length to be set per-channel by making
snps,axi-max-burst-len an array.

Signed-off-by: Phil Elwell <phil@raspberrypi.com>

Author: pelwell

drivers/dma/dw-axi-dmac/dw-axi-dmac-platform.c

@@ -809,7 +809,7 @@ static int dw_axi_dma_set_hw_desc(struct axi_dma_chan *chan,
 	ctlhi = CH_CTL_H_LLI_VALID;
 
 	if (chan->chip->dw->hdata->restrict_axi_burst_len) {
-		burst_len = chan->chip->dw->hdata->axi_rw_burst_len;
+		burst_len = chan->chip->dw->hdata->axi_rw_burst_len[chan->id];
 		ctlhi |= CH_CTL_H_ARLEN_EN | CH_CTL_H_AWLEN_EN |
 			 burst_len << CH_CTL_H_ARLEN_POS |
 			 burst_len << CH_CTL_H_AWLEN_POS;
@@ -1087,7 +1087,7 @@ dma_chan_prep_dma_memcpy(struct dma_chan *dchan, dma_addr_t dst_adr,
 
 		reg = CH_CTL_H_LLI_VALID;
 		if (chan->chip->dw->hdata->restrict_axi_burst_len) {
-			u32 burst_len = chan->chip->dw->hdata->axi_rw_burst_len;
+			u32 burst_len = chan->chip->dw->hdata->axi_rw_burst_len[chan->id];
 
 			reg |= (CH_CTL_H_ARLEN_EN |
 				burst_len << CH_CTL_H_ARLEN_POS |
@@ -1496,6 +1496,7 @@ static int parse_device_properties(struct axi_dma_chip *chip)
 {
 	struct device *dev = chip->dev;
 	u32 tmp, carr[DMAC_MAX_CHANNELS];
+	u32 val;
 	int ret;
 
 	ret = device_property_read_u32(dev, "dma-channels", &tmp);
@@ -1552,15 +1553,21 @@ static int parse_device_properties(struct axi_dma_chip *chip)
 	}
 
 	/* axi-max-burst-len is optional property */
-	ret = device_property_read_u32(dev, "snps,axi-max-burst-len", &tmp);
-	if (!ret) {
-		if (tmp > DWAXIDMAC_ARWLEN_MAX + 1)
-			return -EINVAL;
-		if (tmp < DWAXIDMAC_ARWLEN_MIN + 1)
-			return -EINVAL;
-
+	ret = device_property_read_u32_array(dev, "snps,axi-max-burst-len", NULL,
+					     chip->dw->hdata->nr_channels);
+	if ((ret > 0) &&
+	    !device_property_read_u32_array(dev, "snps,axi-max-burst-len",
+					    carr, ret)) {
 		chip->dw->hdata->restrict_axi_burst_len = true;
-		chip->dw->hdata->axi_rw_burst_len = tmp;
+		for (tmp = 0; tmp < chip->dw->hdata->nr_channels; tmp++) {
+			// Replicate the last value to any remaining channels
+			val = carr[min(tmp, (u32)ret - 1)];
+			if (val > DWAXIDMAC_ARWLEN_MAX + 1)
+				return -EINVAL;
+			if (val < DWAXIDMAC_ARWLEN_MIN + 1)
+				return -EINVAL;
+			chip->dw->hdata->axi_rw_burst_len[tmp] = val;
+		}
 	}
 
 	return 0;
@@ -1674,7 +1681,7 @@ static int dw_probe(struct platform_device *pdev)
 	dma_cap_set(DMA_CYCLIC, dw->dma.cap_mask);
 
 	/* DMA capabilities */
-	dw->dma.max_burst = hdata->axi_rw_burst_len;
+	dw->dma.max_burst = hdata->axi_rw_burst_len[0];
 	dw->dma.src_addr_widths = AXI_DMA_BUSWIDTHS;
 	dw->dma.dst_addr_widths = AXI_DMA_BUSWIDTHS;
 	dw->dma.directions = BIT(DMA_MEM_TO_MEM);

drivers/dma/dw-axi-dmac/dw-axi-dmac.h

@@ -29,7 +29,7 @@ struct dw_axi_dma_hcfg {
 	u32	block_size[DMAC_MAX_CHANNELS];
 	u32	priority[DMAC_MAX_CHANNELS];
 	/* maximum supported axi burst length */
-	u32	axi_rw_burst_len;
+	u32	axi_rw_burst_len[DMAC_MAX_CHANNELS];
 	/* Register map for DMAX_NUM_CHANNELS <= 8 */
 	bool	reg_map_8_channels;
 	bool	restrict_axi_burst_len;