openwrt/target/linux/bcm27xx/patches-6.12/950-0495-drivers-dw-axi-dmac-make-more-sensible-choices-about.patch

From e5d4be923f4ab4d3bd6bb8ea85654df0be27301f Mon Sep 17 00:00:00 2001
From: Jonathan Bell <jonathan@raspberrypi.com>
Date: Fri, 19 Jul 2024 15:55:56 +0100
Subject: [PATCH] drivers: dw-axi-dmac: make more sensible choices about memory
 accesses

There's no real need to constrain MEM access widths to 32-bit (or
narrower), as the DMAC is intelligent enough to size memory accesses
appropriately. Wider accesses are more efficient.

Similarly, MEM burst lengths don't need to be a function of DEV burst
lengths - the DMAC packs/unpacks data into/from its internal channel
FIFOs appropriately. Longer accesses are more efficient.

However, the DMAC doesn't have complete support for unaligned accesses,
and blocks are always defined in integer multiples of SRC_WIDTH, so odd
source lengths or buffer alignments will prevent wide accesses being
used, as before.

There is an implicit requirement to limit requested DEV read burst
lengths to less than the hardware's maximum configured MSIZE - otherwise
RX data will be left over at the end of a block. There is no config
register that reports this value, so the AXI burst length parameter is
used to produce a facsimile of it. Warn if such a request arrives that
doesn't respect this.

Signed-off-by: Jonathan Bell <jonathan@raspberrypi.com>
---
 .../dma/dw-axi-dmac/dw-axi-dmac-platform.c    | 38 ++++++++++++-------
 1 file changed, 25 insertions(+), 13 deletions(-)

--- a/drivers/dma/dw-axi-dmac/dw-axi-dmac-platform.c
+++ b/drivers/dma/dw-axi-dmac/dw-axi-dmac-platform.c
@@ -307,6 +307,15 @@ static u32 axi_chan_get_xfer_width(struc
 	return __ffs(src | dst | len | BIT(max_width));
 }
 
+static u32 axi_dma_encode_msize(u32 max_burst)
+{
+	if (max_burst <= 1)
+		return DWAXIDMAC_BURST_TRANS_LEN_1;
+	if (max_burst > 1024)
+		return DWAXIDMAC_BURST_TRANS_LEN_1024;
+	return fls(max_burst) - 2;
+}
+
 static inline const char *axi_chan_name(struct axi_dma_chan *chan)
 {
 	return dma_chan_name(&chan->vc.chan);
@@ -730,41 +739,41 @@ static int dw_axi_dma_set_hw_desc(struct
 	size_t axi_block_ts;
 	size_t block_ts;
 	u32 ctllo, ctlhi;
-	u32 burst_len;
+	u32 burst_len = 0, mem_burst_msize, reg_burst_msize;
 
 	axi_block_ts = chan->chip->dw->hdata->block_size[chan->id];
 
 	mem_width = __ffs(data_width | mem_addr | len);
-	if (mem_width > DWAXIDMAC_TRANS_WIDTH_32)
-		mem_width = DWAXIDMAC_TRANS_WIDTH_32;
 
 	if (!IS_ALIGNED(mem_addr, 4)) {
 		dev_err(chan->chip->dev, "invalid buffer alignment\n");
 		return -EINVAL;
 	}
 
+	/* Use a reasonable upper limit otherwise residue reporting granularity grows large */
+	mem_burst_msize = axi_dma_encode_msize(16);
+
 	switch (chan->direction) {
 	case DMA_MEM_TO_DEV:
+		reg_burst_msize = axi_dma_encode_msize(chan->config.dst_maxburst);
 		reg_width = __ffs(chan->config.dst_addr_width);
 		device_addr = phys_to_dma(chan->chip->dev, chan->config.dst_addr);
 		ctllo = reg_width << CH_CTL_L_DST_WIDTH_POS |
 			mem_width << CH_CTL_L_SRC_WIDTH_POS |
-			DWAXIDMAC_BURST_TRANS_LEN_1 << CH_CTL_L_DST_MSIZE_POS |
-			DWAXIDMAC_BURST_TRANS_LEN_4 << CH_CTL_L_SRC_MSIZE_POS |
+			reg_burst_msize << CH_CTL_L_DST_MSIZE_POS |
+			mem_burst_msize << CH_CTL_L_SRC_MSIZE_POS |
 			DWAXIDMAC_CH_CTL_L_NOINC << CH_CTL_L_DST_INC_POS |
 			DWAXIDMAC_CH_CTL_L_INC << CH_CTL_L_SRC_INC_POS;
 		block_ts = len >> mem_width;
 		break;
 	case DMA_DEV_TO_MEM:
+		reg_burst_msize = axi_dma_encode_msize(chan->config.src_maxburst);
 		reg_width = __ffs(chan->config.src_addr_width);
-		/* Prevent partial access units getting lost */
-		if (mem_width > reg_width)
-			mem_width = reg_width;
 		device_addr = phys_to_dma(chan->chip->dev, chan->config.src_addr);
 		ctllo = reg_width << CH_CTL_L_SRC_WIDTH_POS |
 			mem_width << CH_CTL_L_DST_WIDTH_POS |
-			DWAXIDMAC_BURST_TRANS_LEN_4 << CH_CTL_L_DST_MSIZE_POS |
-			DWAXIDMAC_BURST_TRANS_LEN_1 << CH_CTL_L_SRC_MSIZE_POS |
+			mem_burst_msize << CH_CTL_L_DST_MSIZE_POS |
+			reg_burst_msize << CH_CTL_L_SRC_MSIZE_POS |
 			DWAXIDMAC_CH_CTL_L_INC << CH_CTL_L_DST_INC_POS |
 			DWAXIDMAC_CH_CTL_L_NOINC << CH_CTL_L_SRC_INC_POS;
 		block_ts = len >> reg_width;
@@ -805,6 +814,12 @@ static int dw_axi_dma_set_hw_desc(struct
 	set_desc_src_master(hw_desc);
 
 	hw_desc->len = len;
+
+	if (burst_len && (chan->config.src_maxburst > burst_len))
+		dev_warn_ratelimited(chan2dev(chan),
+				     "%s: requested source burst length %u exceeds supported burst length %u - data may be lost\n",
+				     axi_chan_name(chan), chan->config.src_maxburst, burst_len);
+
 	return 0;
 }
 
@@ -821,9 +836,6 @@ static size_t calculate_block_len(struct
 	case DMA_MEM_TO_DEV:
 		data_width = BIT(chan->chip->dw->hdata->m_data_width);
 		mem_width = __ffs(data_width | dma_addr | buf_len);
-		if (mem_width > DWAXIDMAC_TRANS_WIDTH_32)
-			mem_width = DWAXIDMAC_TRANS_WIDTH_32;
-
 		block_len = axi_block_ts << mem_width;
 		break;
 	case DMA_DEV_TO_MEM: