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Merged
pelwell merged 3 commits into from
Oct 16, 2025
Merged

Improve the RP1 DMA channel allocation scheme #7089

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ee95e6a
fixup! dmaengine: dw-axi-dmac: Add DMA channel selection
pelwell Oct 13, 2025
9129853
fixup! dts: bcm2712-rpi: Give PIO the "heavy" DMA channels
pelwell Oct 13, 2025
12dfd6c
misc: rp1-pio: Get burst size from DMA capabilities
pelwell Oct 14, 2025
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23 changes: 10 additions & 13 deletions arch/arm64/boot/dts/broadcom/bcm2712-rpi.dtsi
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Original file line number Diff line number Diff line change
Expand Up @@ -2,8 +2,7 @@

#include <dt-bindings/power/raspberrypi-power.h>

#define DMA_SEL_WANTHEAVY (1 << 8)
#define DMA_SEL_ONLYHEAVY (1 << 9)
#define DMA_FLAG_HEAVY (1 << 8)

&soc {
firmware: firmware {
Expand Down Expand Up @@ -95,20 +94,18 @@
};

&rp1_dma {
snps,sel-require = <DMA_SEL_WANTHEAVY DMA_SEL_WANTHEAVY 0 0 0 0 0 0>;
snps,sel-preclude = <0 0 DMA_SEL_ONLYHEAVY DMA_SEL_ONLYHEAVY DMA_SEL_ONLYHEAVY
DMA_SEL_ONLYHEAVY DMA_SEL_ONLYHEAVY DMA_SEL_ONLYHEAVY>;
snps,chan-flags = <DMA_FLAG_HEAVY DMA_FLAG_HEAVY 0 0 0 0 0 0>;
};

pio: &rp1_pio {
dmas = <&rp1_dma (RP1_DMA_PIO_CH0_TX | DMA_SEL_WANTHEAVY)>,
<&rp1_dma (RP1_DMA_PIO_CH0_RX | DMA_SEL_WANTHEAVY)>,
<&rp1_dma (RP1_DMA_PIO_CH1_TX | DMA_SEL_WANTHEAVY)>,
<&rp1_dma (RP1_DMA_PIO_CH1_RX | DMA_SEL_WANTHEAVY)>,
<&rp1_dma (RP1_DMA_PIO_CH2_TX | DMA_SEL_WANTHEAVY)>,
<&rp1_dma (RP1_DMA_PIO_CH2_RX | DMA_SEL_WANTHEAVY)>,
<&rp1_dma (RP1_DMA_PIO_CH3_TX | DMA_SEL_WANTHEAVY)>,
<&rp1_dma (RP1_DMA_PIO_CH3_RX | DMA_SEL_WANTHEAVY)>;
dmas = <&rp1_dma (RP1_DMA_PIO_CH0_TX | DMA_FLAG_HEAVY)>,
<&rp1_dma (RP1_DMA_PIO_CH0_RX | DMA_FLAG_HEAVY)>,
<&rp1_dma (RP1_DMA_PIO_CH1_TX | DMA_FLAG_HEAVY)>,
<&rp1_dma (RP1_DMA_PIO_CH1_RX | DMA_FLAG_HEAVY)>,
<&rp1_dma (RP1_DMA_PIO_CH2_TX | DMA_FLAG_HEAVY)>,
<&rp1_dma (RP1_DMA_PIO_CH2_RX | DMA_FLAG_HEAVY)>,
<&rp1_dma (RP1_DMA_PIO_CH3_TX | DMA_FLAG_HEAVY)>,
<&rp1_dma (RP1_DMA_PIO_CH3_RX | DMA_FLAG_HEAVY)>;
status = "okay";
};

Expand Down
80 changes: 53 additions & 27 deletions drivers/dma/dw-axi-dmac/dw-axi-dmac-platform.c
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Original file line number Diff line number Diff line change
Expand Up @@ -1499,33 +1499,62 @@ static struct dma_chan *dw_axi_dma_of_xlate(struct of_phandle_args *dma_spec,
{
struct dw_axi_dma *dw = ofdma->of_dma_data;
struct axi_dma_chan *chan;
uint32_t chan_flags_all;
uint32_t busy_channels;
struct dma_chan *dchan;
uint32_t chan_mask = 0;
uint32_t chan_sel;
dma_cap_mask_t mask;
uint32_t chan_mask;
uint32_t chan_sel;
int max_score;
int score;
int i;

/*
* Walk through all channels looking for the best match.
* Starting from 0, choose the first available slave channel which isn't precluded.
*/
chan_sel = dma_spec->args[0];

for (i = 0; i < dw->hdata->nr_channels; i++) {
if (((dw->sel_precluded[i] & chan_sel) == 0) &&
((dw->sel_required[i] & chan_sel) == dw->sel_required[i]))
chan_mask |= (1 << i);
}
for (i = 0; i < dw->hdata->nr_channels; i++)
chan_flags_all |= dw->chan_flags[i];

dma_cap_zero(mask);
dma_cap_set(DMA_SLAVE, mask);

dchan = __dma_request_channel(&mask, dw_axi_dma_filter_fn, &chan_mask, ofdma->of_node);
if (!dchan)
return NULL;
chan_sel = dma_spec->args[0];
busy_channels = 0;
dchan = NULL;

while (1) {
max_score = 0;
chan_mask = 0;

for (i = 0; i < dw->hdata->nr_channels; i++) {
if (busy_channels & (1 << i))
continue;
/*
* Positive matches (wanted flags that match) score twice that of
* negetive matches (not wanted flags that are not present).
*/
score = 2 * hweight32(chan_sel & dw->chan_flags[i]) +
1 * hweight32(~chan_sel & ~dw->chan_flags[i] & chan_flags_all);
if (score > max_score) {
max_score = score;
chan_mask = (1 << i);
} else if (score == max_score) {
chan_mask |= (1 << i);
}
}

if (!chan_mask)
return NULL;

dchan = __dma_request_channel(&mask, dw_axi_dma_filter_fn,
&chan_mask, ofdma->of_node);
if (dchan)
break;

/* Repeat, after first marking this group of channels as busy */
busy_channels |= chan_mask;
}

chan = dchan_to_axi_dma_chan(dchan);
chan->hw_handshake_num = (u8)chan_sel;

return dchan;
}

Expand Down Expand Up @@ -1607,17 +1636,14 @@ static int parse_device_properties(struct axi_dma_chip *chip)
}
}

/* sel-require is optional */
memset(chip->dw->sel_required, 0, sizeof(chip->dw->sel_required));
device_property_read_u32_array(dev, "snps,sel-require",
chip->dw->sel_required,
chip->dw->hdata->nr_channels);

/* sel-preclude is optional */
memset(chip->dw->sel_precluded, 0, sizeof(chip->dw->sel_precluded));
device_property_read_u32_array(dev, "snps,sel-preclude",
chip->dw->sel_precluded,
chip->dw->hdata->nr_channels);
/* snps,chan-flags is optional */
memset(chip->dw->chan_flags, 0, sizeof(chip->dw->chan_flags));
if (device_property_read_u32_array(dev, "snps,chan-flags",
chip->dw->chan_flags,
chip->dw->hdata->nr_channels) < 0)
device_property_read_u32_array(dev, "snps,sel-require",
chip->dw->chan_flags,
chip->dw->hdata->nr_channels);

return 0;
}
Expand Down
3 changes: 1 addition & 2 deletions drivers/dma/dw-axi-dmac/dw-axi-dmac.h
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Original file line number Diff line number Diff line change
Expand Up @@ -58,8 +58,7 @@ struct dw_axi_dma {
struct dma_device dma;
struct dw_axi_dma_hcfg *hdata;
struct device_dma_parameters dma_parms;
u32 sel_required[DMAC_MAX_CHANNELS];
u32 sel_precluded[DMAC_MAX_CHANNELS];
u32 chan_flags[DMAC_MAX_CHANNELS];

/* channels */
struct axi_dma_chan *chan;
Expand Down
7 changes: 5 additions & 2 deletions drivers/misc/rp1-pio.c
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Original file line number Diff line number Diff line change
Expand Up @@ -611,6 +611,7 @@ static int rp1_pio_sm_config_xfer_internal(struct rp1_pio_client *client, uint s
struct platform_device *pdev = pio->pdev;
struct device *dev = &pdev->dev;
struct dma_slave_config config = {};
struct dma_slave_caps dma_caps;
phys_addr_t fifo_addr;
struct dma_info *dma;
uint32_t dma_mask;
Expand Down Expand Up @@ -676,10 +677,12 @@ static int rp1_pio_sm_config_xfer_internal(struct rp1_pio_client *client, uint s
config.src_addr = fifo_addr;
config.dst_addr = fifo_addr;
config.direction = (dir == RP1_PIO_DIR_TO_SM) ? DMA_MEM_TO_DEV : DMA_DEV_TO_MEM;
dma_caps.max_burst = 4;
dma_get_slave_caps(dma->chan, &dma_caps);
if (dir == RP1_PIO_DIR_TO_SM)
config.dst_maxburst = 8;
config.dst_maxburst = dma_caps.max_burst;
else
config.src_maxburst = 8;
config.src_maxburst = dma_caps.max_burst;

ret = dmaengine_slave_config(dma->chan, &config);
if (ret)
Expand Down