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bcm2835-sdhost: Only claim one DMA channel
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With both MMC controllers enabled there are few DMA channels left. The
bcm2835-sdhost driver only uses DMA in one direction at a time, so it
doesn't need to claim two channels.

See: raspberrypi#1327

Signed-off-by: Phil Elwell <phil@raspberrypi.org>
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Phil Elwell committed Mar 8, 2016
1 parent 48f3f77 commit 06c1699
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Showing 2 changed files with 50 additions and 25 deletions.
5 changes: 2 additions & 3 deletions arch/arm/boot/dts/bcm2708_common.dtsi
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Original file line number Diff line number Diff line change
Expand Up @@ -136,9 +136,8 @@
reg = <0x7e202000 0x100>;
interrupts = <2 24>;
clocks = <&clk_core>;
dmas = <&dma 13>,
<&dma 13>;
dma-names = "tx", "rx";
dmas = <&dma 13>;
dma-names = "rx-tx";
brcm,overclock-50 = <0>;
brcm,pio-limit = <1>;
status = "disabled";
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70 changes: 48 additions & 22 deletions drivers/mmc/host/bcm2835-sdhost.c
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Original file line number Diff line number Diff line change
Expand Up @@ -185,9 +185,10 @@ struct bcm2835_host {
unsigned int debug:1; /* Enable debug output */

/*DMA part*/
struct dma_chan *dma_chan_rx; /* DMA channel for reads */
struct dma_chan *dma_chan_tx; /* DMA channel for writes */
struct dma_chan *dma_chan; /* Channel in used */
struct dma_chan *dma_chan_rxtx; /* DMA channel for reads and writes */
struct dma_chan *dma_chan; /* Channel in use */
struct dma_slave_config dma_cfg_rx;
struct dma_slave_config dma_cfg_tx;
struct dma_async_tx_descriptor *dma_desc;
u32 dma_dir;
u32 drain_words;
Expand Down Expand Up @@ -771,12 +772,11 @@ static void bcm2835_sdhost_prepare_dma(struct bcm2835_host *host,
log_event("PRD<", (u32)data, 0);
pr_debug("bcm2835_sdhost_prepare_dma()\n");

dma_chan = host->dma_chan_rxtx;
if (data->flags & MMC_DATA_READ) {
dma_chan = host->dma_chan_rx;
dir_data = DMA_FROM_DEVICE;
dir_slave = DMA_DEV_TO_MEM;
} else {
dma_chan = host->dma_chan_tx;
dir_data = DMA_TO_DEVICE;
dir_slave = DMA_MEM_TO_DEV;
}
Expand Down Expand Up @@ -813,6 +813,12 @@ static void bcm2835_sdhost_prepare_dma(struct bcm2835_host *host,
host->drain_words = len/4;
}

/* The parameters have already been validated, so this will not fail */
(void)dmaengine_slave_config(dma_chan,
(dir_data == DMA_FROM_DEVICE) ?
&host->dma_cfg_rx :
&host->dma_cfg_tx);

len = dma_map_sg(dma_chan->device->dev, data->sg, data->sg_len,
dir_data);

Expand Down Expand Up @@ -1805,28 +1811,46 @@ int bcm2835_sdhost_add_host(struct bcm2835_host *host)
spin_lock_init(&host->lock);

if (host->allow_dma) {
if (IS_ERR_OR_NULL(host->dma_chan_tx) ||
IS_ERR_OR_NULL(host->dma_chan_rx)) {
pr_err("%s: unable to initialise DMA channels. "
if (IS_ERR_OR_NULL(host->dma_chan_rxtx)) {
pr_err("%s: unable to initialise DMA channel. "
"Falling back to PIO\n",
mmc_hostname(mmc));
host->use_dma = false;
} else {
host->use_dma = true;

cfg.src_addr_width = DMA_SLAVE_BUSWIDTH_4_BYTES;
cfg.dst_addr_width = DMA_SLAVE_BUSWIDTH_4_BYTES;
cfg.slave_id = 13; /* DREQ channel */

/* Validate the slave configurations */

cfg.direction = DMA_MEM_TO_DEV;
cfg.src_addr = 0;
cfg.dst_addr = host->bus_addr + SDDATA;
ret = dmaengine_slave_config(host->dma_chan_tx, &cfg);

cfg.direction = DMA_DEV_TO_MEM;
cfg.src_addr = host->bus_addr + SDDATA;
cfg.dst_addr = 0;
ret = dmaengine_slave_config(host->dma_chan_rx, &cfg);
ret = dmaengine_slave_config(host->dma_chan_rxtx, &cfg);

if (ret == 0) {
host->dma_cfg_tx = cfg;

cfg.direction = DMA_DEV_TO_MEM;
cfg.src_addr = host->bus_addr + SDDATA;
cfg.dst_addr = 0;

ret = dmaengine_slave_config(host->dma_chan_rxtx, &cfg);
}

if (ret == 0) {
host->dma_cfg_rx = cfg;

host->use_dma = true;
} else {
pr_err("%s: unable to configure DMA channel. "
"Falling back to PIO\n",
mmc_hostname(mmc));
dma_release_channel(host->dma_chan_rxtx);
host->dma_chan_rxtx = NULL;
host->use_dma = false;
}
}
} else {
host->use_dma = false;
Expand Down Expand Up @@ -1948,19 +1972,21 @@ static int bcm2835_sdhost_probe(struct platform_device *pdev)

if (host->allow_dma) {
if (node) {
host->dma_chan_tx =
dma_request_slave_channel(dev, "tx");
host->dma_chan_rx =
dma_request_slave_channel(dev, "rx");
host->dma_chan_rxtx =
dma_request_slave_channel(dev, "rx-tx");
if (!host->dma_chan_rxtx)
host->dma_chan_rxtx =
dma_request_slave_channel(dev, "tx");
if (!host->dma_chan_rxtx)
host->dma_chan_rxtx =
dma_request_slave_channel(dev, "rx");
} else {
dma_cap_mask_t mask;

dma_cap_zero(mask);
/* we don't care about the channel, any would work */
dma_cap_set(DMA_SLAVE, mask);
host->dma_chan_tx =
dma_request_channel(mask, NULL, NULL);
host->dma_chan_rx =
host->dma_chan_rxtx =
dma_request_channel(mask, NULL, NULL);
}
}
Expand Down

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