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spi: dw: Save bandwidth with the TMOD_RO feature

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TMOD_RO is the receive-only mode that doesn't require data in the
transmit FIFO in order to generate clock cycles. Using TMOD_RO when the
device doesn't care about the data sent to it saves CPU time and memory
bandwidth.

Signed-off-by: Phil Elwell <phil@raspberrypi.com>
This commit is contained in:
Phil Elwell
2024-07-01 16:41:04 +01:00
committed by Dom Cobley
parent 0624721570
commit d9a3c87a44
2 changed files with 52 additions and 22 deletions
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31
drivers/spi/spi-dw-core.c
View File

@@ -369,18 +369,18 @@ static void dw_spi_irq_setup(struct dw_spi *dws)
* will be adjusted at the final stage of the IRQ-based SPI transfer
* execution so not to lose the leftover of the incoming data.
*/
level = min_t(unsigned int, dws->fifo_len / 2, dws->tx_len);
level = min_t(unsigned int, dws->fifo_len / 2, dws->tx_len ? dws->tx_len : dws->rx_len);
dw_writel(dws, DW_SPI_TXFTLR, level);
dw_writel(dws, DW_SPI_RXFTLR, level - 1);
dws->transfer_handler = dw_spi_transfer_handler;
imask = 0;
if (dws->tx_len)
imask |= DW_SPI_INT_TXEI | DW_SPI_INT_TXOI;
imask = DW_SPI_INT_TXEI | DW_SPI_INT_TXOI;
if (dws->rx_len)
imask |= DW_SPI_INT_RXUI | DW_SPI_INT_RXOI | DW_SPI_INT_RXFI;
dw_spi_umask_intr(dws, imask);
if (!dws->tx_len)
dw_writel(dws, DW_SPI_DR, 0);
}
/*
@@ -403,13 +403,18 @@ static int dw_spi_poll_transfer(struct dw_spi *dws,
delay.unit = SPI_DELAY_UNIT_SCK;
nbits = dws->n_bytes * BITS_PER_BYTE;
if (!dws->tx_len)
dw_writel(dws, DW_SPI_DR, 0);
do {
dw_writer(dws);
if (dws->tx_len)
dw_writer(dws);
delay.value = nbits * (dws->rx_len - dws->tx_len);
spi_delay_exec(&delay, transfer);
dw_reader(dws);
if (dws->rx_len)
dw_reader(dws);
ret = dw_spi_check_status(dws, true);
if (ret)
@@ -429,6 +434,7 @@ static int dw_spi_transfer_one(struct spi_controller *host,
.dfs = transfer->bits_per_word,
.freq = transfer->speed_hz,
};
int buswidth;
int ret;
dws->dma_mapped = 0;
@@ -443,6 +449,18 @@ static int dw_spi_transfer_one(struct spi_controller *host,
cfg.tmode = DW_SPI_CTRLR0_TMOD_TO;
}
if (!dws->rx) {
dws->rx_len = 0;
cfg.tmode = DW_SPI_CTRLR0_TMOD_TO;
}
if (!dws->tx) {
dws->tx_len = 0;
cfg.tmode = DW_SPI_CTRLR0_TMOD_RO;
cfg.ndf = dws->rx_len;
}
buswidth = transfer->rx_buf ? transfer->rx_nbits :
(transfer->tx_buf ? transfer->tx_nbits : 1);
/* Ensure the data above is visible for all CPUs */
smp_mb();
@@ -979,7 +997,6 @@ int dw_spi_add_host(struct device *dev, struct dw_spi *dws)
dev_warn(dev, "DMA init failed\n");
} else {
host->can_dma = dws->dma_ops->can_dma;
host->flags |= SPI_CONTROLLER_MUST_TX;
}
}

43
drivers/spi/spi-dw-dma.c
View File

@@ -6,6 +6,7 @@
*/
#include <linux/completion.h>
#include <linux/delay.h>
#include <linux/dma-mapping.h>
#include <linux/dmaengine.h>
#include <linux/irqreturn.h>
@@ -470,13 +471,12 @@ static int dw_spi_dma_setup(struct dw_spi *dws, struct spi_transfer *xfer)
u16 imr, dma_ctrl;
int ret;
if (!xfer->tx_buf)
return -EINVAL;
/* Setup DMA channels */
ret = dw_spi_dma_config_tx(dws);
if (ret)
return ret;
if (xfer->tx_buf) {
ret = dw_spi_dma_config_tx(dws);
if (ret)
return ret;
}
if (xfer->rx_buf) {
ret = dw_spi_dma_config_rx(dws);
@@ -485,13 +485,17 @@ static int dw_spi_dma_setup(struct dw_spi *dws, struct spi_transfer *xfer)
}
/* Set the DMA handshaking interface */
dma_ctrl = DW_SPI_DMACR_TDMAE;
dma_ctrl = 0;
if (xfer->tx_buf)
dma_ctrl |= DW_SPI_DMACR_TDMAE;
if (xfer->rx_buf)
dma_ctrl |= DW_SPI_DMACR_RDMAE;
dw_writel(dws, DW_SPI_DMACR, dma_ctrl);
/* Set the interrupt mask */
imr = DW_SPI_INT_TXOI;
imr = 0;
if (xfer->tx_buf)
imr |= DW_SPI_INT_TXOI;
if (xfer->rx_buf)
imr |= DW_SPI_INT_RXUI | DW_SPI_INT_RXOI;
dw_spi_umask_intr(dws, imr);
@@ -508,15 +512,16 @@ static int dw_spi_dma_transfer_all(struct dw_spi *dws,
{
int ret;
/* Submit the DMA Tx transfer */
ret = dw_spi_dma_submit_tx(dws, xfer->tx_sg.sgl, xfer->tx_sg.nents);
if (ret)
goto err_clear_dmac;
/* Submit the DMA Tx transfer if required */
if (xfer->tx_buf) {
ret = dw_spi_dma_submit_tx(dws, xfer->tx_sg.sgl, xfer->tx_sg.nents);
if (ret)
goto err_clear_dmac;
}
/* Submit the DMA Rx transfer if required */
if (xfer->rx_buf) {
ret = dw_spi_dma_submit_rx(dws, xfer->rx_sg.sgl,
xfer->rx_sg.nents);
ret = dw_spi_dma_submit_rx(dws, xfer->rx_sg.sgl, xfer->rx_sg.nents);
if (ret)
goto err_clear_dmac;
@@ -524,7 +529,15 @@ static int dw_spi_dma_transfer_all(struct dw_spi *dws,
dma_async_issue_pending(dws->rxchan);
}
dma_async_issue_pending(dws->txchan);
if (xfer->tx_buf) {
dma_async_issue_pending(dws->txchan);
} else {
/* Pause to allow DMA channel to fetch RX descriptor */
usleep_range(5, 10);
/* Write something to the TX FIFO to start the transfer */
dw_writel(dws, DW_SPI_DR, 0);
}
ret = dw_spi_dma_wait(dws, xfer->len, xfer->effective_speed_hz);