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spi: bcm2835: enable dma modes for transfers meeting certain conditions

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Conditions per spi_transfer are:
* transfer.len >= 96 bytes (to avoid mapping overhead costs)
* transfer.len < 65536 bytes (limitaion by spi-hw block - could get extended)
* an individual scatter/gather transfer length must be a multiple of 4
  for anything but the last transfer - spi-hw block limit.
  (some shortcut has been taken in can_dma to avoid unnecessary mapping of
   pages which, for which there is a chance that there is a split with a
   transfer length not a multiple of 4)

If it becomes a necessity these restrictions can get removed by additional
code.

Note that this patch requires a patch to dma-bcm2835.c by Noralf to
enable scatter-gather mode inside the dmaengine, which has not been
merged yet.

That is why no patch to arch/arm/boot/dts/bcm2835.dtsi is included - the
code works as before without dma when tx/rx are not set, but it writes
a message warning about dma not used:
spi-bcm2835 20204000.spi: no tx-dma configuration found - not using dma mode

To enable dma-mode add the following lines to the device-tree:
        dmas = <&dma 6>, <&dma 7>;
        dma-names = "tx", "rx";

Tested-by: Noralf Trønnes <noralf@tronnes.org> (private communication)
Signed-off-by: Martin Sperl <kernel@martin.sperl.org>
Signed-off-by: Mark Brown <broonie@kernel.org>
This commit is contained in:
Martin Sperl 2015-05-10 20:47:28 +00:00 committed by Mark Brown
parent e0d58cdcae
commit 3ecd37edaa
1 changed files with 301 additions and 2 deletions
repo.diff.show_diff_stats Download patch file Download diff file Expand all files Collapse all files

303
drivers/spi/spi-bcm2835.c
View file

@ -23,15 +23,18 @@
#include <linux/clk.h>
#include <linux/completion.h>
#include <linux/delay.h>
#include <linux/dma-mapping.h>
#include <linux/dmaengine.h>
#include <linux/err.h>
#include <linux/interrupt.h>
#include <linux/io.h>
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/of.h>
#include <linux/of_irq.h>
#include <linux/of_gpio.h>
#include <linux/of_address.h>
#include <linux/of_device.h>
#include <linux/of_gpio.h>
#include <linux/of_irq.h>
#include <linux/spi/spi.h>
/* SPI register offsets */
@ -70,6 +73,7 @@
#define BCM2835_SPI_POLLING_LIMIT_US 30
#define BCM2835_SPI_POLLING_JIFFIES 2
#define BCM2835_SPI_DMA_MIN_LENGTH 96
#define BCM2835_SPI_MODE_BITS (SPI_CPOL | SPI_CPHA | SPI_CS_HIGH \
| SPI_NO_CS | SPI_3WIRE)
@ -83,6 +87,7 @@ struct bcm2835_spi {
u8 *rx_buf;
int tx_len;
int rx_len;
bool dma_pending;
};
static inline u32 bcm2835_rd(struct bcm2835_spi *bs, unsigned reg)
@ -128,12 +133,15 @@ static void bcm2835_spi_reset_hw(struct spi_master *master)
/* Disable SPI interrupts and transfer */
cs &= ~(BCM2835_SPI_CS_INTR |
BCM2835_SPI_CS_INTD |
BCM2835_SPI_CS_DMAEN |
BCM2835_SPI_CS_TA);
/* and reset RX/TX FIFOS */
cs |= BCM2835_SPI_CS_CLEAR_RX | BCM2835_SPI_CS_CLEAR_TX;
/* and reset the SPI_HW */
bcm2835_wr(bs, BCM2835_SPI_CS, cs);
/* as well as DLEN */
bcm2835_wr(bs, BCM2835_SPI_DLEN, 0);
}
static irqreturn_t bcm2835_spi_interrupt(int irq, void *dev_id)
@ -193,6 +201,279 @@ static int bcm2835_spi_transfer_one_irq(struct spi_master *master,
return 1;
}
/*
* DMA support
*
* this implementation has currently a few issues in so far as it does
* not work arrount limitations of the HW.
*
* the main one being that DMA transfers are limited to 16 bit
* (so 0 to 65535 bytes) by the SPI HW due to BCM2835_SPI_DLEN
*
* also we currently assume that the scatter-gather fragments are
* all multiple of 4 (except the last) - otherwise we would need
* to reset the FIFO before subsequent transfers...
* this also means that tx/rx transfers sg's need to be of equal size!
*
* there may be a few more border-cases we may need to address as well
* but unfortunately this would mean splitting up the scatter-gather
* list making it slightly unpractical...
*/
static void bcm2835_spi_dma_done(void *data)
{
struct spi_master *master = data;
struct bcm2835_spi *bs = spi_master_get_devdata(master);
/* reset fifo and HW */
bcm2835_spi_reset_hw(master);
/* and terminate tx-dma as we do not have an irq for it
* because when the rx dma will terminate and this callback
* is called the tx-dma must have finished - can't get to this
* situation otherwise...
*/
dmaengine_terminate_all(master->dma_tx);
/* mark as no longer pending */
bs->dma_pending = 0;
/* and mark as completed */;
complete(&master->xfer_completion);
}
static int bcm2835_spi_prepare_sg(struct spi_master *master,
struct spi_transfer *tfr,
bool is_tx)
{
struct dma_chan *chan;
struct scatterlist *sgl;
unsigned int nents;
enum dma_transfer_direction dir;
unsigned long flags;
struct dma_async_tx_descriptor *desc;
dma_cookie_t cookie;
if (is_tx) {
dir = DMA_MEM_TO_DEV;
chan = master->dma_tx;
nents = tfr->tx_sg.nents;
sgl = tfr->tx_sg.sgl;
flags = 0 /* no tx interrupt */;
} else {
dir = DMA_DEV_TO_MEM;
chan = master->dma_rx;
nents = tfr->rx_sg.nents;
sgl = tfr->rx_sg.sgl;
flags = DMA_PREP_INTERRUPT;
}
/* prepare the channel */
desc = dmaengine_prep_slave_sg(chan, sgl, nents, dir, flags);
if (!desc)
return -EINVAL;
/* set callback for rx */
if (!is_tx) {
desc->callback = bcm2835_spi_dma_done;
desc->callback_param = master;
}
/* submit it to DMA-engine */
cookie = dmaengine_submit(desc);
return dma_submit_error(cookie);
}
static inline int bcm2835_check_sg_length(struct sg_table *sgt)
{
int i;
struct scatterlist *sgl;
/* check that the sg entries are word-sized (except for last) */
for_each_sg(sgt->sgl, sgl, (int)sgt->nents - 1, i) {
if (sg_dma_len(sgl) % 4)
return -EFAULT;
}
return 0;
}
static int bcm2835_spi_transfer_one_dma(struct spi_master *master,
struct spi_device *spi,
struct spi_transfer *tfr,
u32 cs)
{
struct bcm2835_spi *bs = spi_master_get_devdata(master);
int ret;
/* check that the scatter gather segments are all a multiple of 4 */
if (bcm2835_check_sg_length(&tfr->tx_sg) ||
bcm2835_check_sg_length(&tfr->rx_sg)) {
dev_warn_once(&spi->dev,
"scatter gather segment length is not a multiple of 4 - falling back to interrupt mode\n");
return bcm2835_spi_transfer_one_irq(master, spi, tfr, cs);
}
/* setup tx-DMA */
ret = bcm2835_spi_prepare_sg(master, tfr, true);
if (ret)
return ret;
/* start TX early */
dma_async_issue_pending(master->dma_tx);
/* mark as dma pending */
bs->dma_pending = 1;
/* set the DMA length */
bcm2835_wr(bs, BCM2835_SPI_DLEN, tfr->len);
/* start the HW */
bcm2835_wr(bs, BCM2835_SPI_CS,
cs | BCM2835_SPI_CS_TA | BCM2835_SPI_CS_DMAEN);
/* setup rx-DMA late - to run transfers while
* mapping of the rx buffers still takes place
* this saves 10us or more.
*/
ret = bcm2835_spi_prepare_sg(master, tfr, false);
if (ret) {
/* need to reset on errors */
dmaengine_terminate_all(master->dma_tx);
bcm2835_spi_reset_hw(master);
return ret;
}
/* start rx dma late */
dma_async_issue_pending(master->dma_rx);
/* wait for wakeup in framework */
return 1;
}
static bool bcm2835_spi_can_dma(struct spi_master *master,
struct spi_device *spi,
struct spi_transfer *tfr)
{
/* only run for gpio_cs */
if (!gpio_is_valid(spi->cs_gpio))
return false;
/* we start DMA efforts only on bigger transfers */
if (tfr->len < BCM2835_SPI_DMA_MIN_LENGTH)
return false;
/* BCM2835_SPI_DLEN has defined a max transfer size as
* 16 bit, so max is 65535
* we can revisit this by using an alternative transfer
* method - ideally this would get done without any more
* interaction...
*/
if (tfr->len > 65535) {
dev_warn_once(&spi->dev,
"transfer size of %d too big for dma-transfer\n",
tfr->len);
return false;
}
/* if we run rx/tx_buf with word aligned addresses then we are OK */
if (((u32)tfr->tx_buf % 4 == 0) && ((u32)tfr->tx_buf % 4 == 0))
return true;
/* otherwise we only allow transfers within the same page
* to avoid wasting time on dma_mapping when it is not practical
*/
if (((u32)tfr->tx_buf % SZ_4K) + tfr->len > SZ_4K) {
dev_warn_once(&spi->dev,
"Unaligned spi tx-transfer bridging page\n");
return false;
}
if (((u32)tfr->rx_buf % SZ_4K) + tfr->len > SZ_4K) {
dev_warn_once(&spi->dev,
"Unaligned spi tx-transfer bridging page\n");
return false;
}
/* return OK */
return true;
}
void bcm2835_dma_release(struct spi_master *master)
{
if (master->dma_tx) {
dmaengine_terminate_all(master->dma_tx);
dma_release_channel(master->dma_tx);
master->dma_tx = NULL;
}
if (master->dma_rx) {
dmaengine_terminate_all(master->dma_rx);
dma_release_channel(master->dma_rx);
master->dma_rx = NULL;
}
}
void bcm2835_dma_init(struct spi_master *master, struct device *dev)
{
struct dma_slave_config slave_config;
const __be32 *addr;
dma_addr_t dma_reg_base;
int ret;
/* base address in dma-space */
addr = of_get_address(master->dev.of_node, 0, NULL, NULL);
if (!addr) {
dev_err(dev, "could not get DMA-register address - not using dma mode\n");
goto err;
}
dma_reg_base = be32_to_cpup(addr);
/* get tx/rx dma */
master->dma_tx = dma_request_slave_channel(dev, "tx");
if (!master->dma_tx) {
dev_err(dev, "no tx-dma configuration found - not using dma mode\n");
goto err;
}
master->dma_rx = dma_request_slave_channel(dev, "rx");
if (!master->dma_rx) {
dev_err(dev, "no rx-dma configuration found - not using dma mode\n");
goto err_release;
}
/* configure DMAs */
slave_config.direction = DMA_MEM_TO_DEV;
slave_config.dst_addr = (u32)(dma_reg_base + BCM2835_SPI_FIFO);
slave_config.dst_addr_width = DMA_SLAVE_BUSWIDTH_4_BYTES;
ret = dmaengine_slave_config(master->dma_tx, &slave_config);
if (ret)
goto err_config;
slave_config.direction = DMA_DEV_TO_MEM;
slave_config.src_addr = (u32)(dma_reg_base + BCM2835_SPI_FIFO);
slave_config.src_addr_width = DMA_SLAVE_BUSWIDTH_4_BYTES;
ret = dmaengine_slave_config(master->dma_rx, &slave_config);
if (ret)
goto err_config;
/* all went well, so set can_dma */
master->can_dma = bcm2835_spi_can_dma;
master->max_dma_len = 65535; /* limitation by BCM2835_SPI_DLEN */
/* need to do TX AND RX DMA, so we need dummy buffers */
master->flags = SPI_MASTER_MUST_RX | SPI_MASTER_MUST_TX;
return;
err_config:
dev_err(dev, "issue configuring dma: %d - not using DMA mode\n",
ret);
err_release:
bcm2835_dma_release(master);
err:
return;
}
static int bcm2835_spi_transfer_one_poll(struct spi_master *master,
struct spi_device *spi,
struct spi_transfer *tfr,
@ -301,12 +582,26 @@ static int bcm2835_spi_transfer_one(struct spi_master *master,
return bcm2835_spi_transfer_one_poll(master, spi, tfr,
cs, xfer_time_us);
/* run in dma mode if conditions are right */
if (master->can_dma && bcm2835_spi_can_dma(master, spi, tfr))
return bcm2835_spi_transfer_one_dma(master, spi, tfr, cs);
/* run in interrupt-mode */
return bcm2835_spi_transfer_one_irq(master, spi, tfr, cs);
}
static void bcm2835_spi_handle_err(struct spi_master *master,
struct spi_message *msg)
{
struct bcm2835_spi *bs = spi_master_get_devdata(master);
/* if an error occurred and we have an active dma, then terminate */
if (bs->dma_pending) {
dmaengine_terminate_all(master->dma_tx);
dmaengine_terminate_all(master->dma_rx);
bs->dma_pending = 0;
}
/* and reset */
bcm2835_spi_reset_hw(master);
}
@ -476,6 +771,8 @@ static int bcm2835_spi_probe(struct platform_device *pdev)
goto out_clk_disable;
}
bcm2835_dma_init(master, &pdev->dev);
/* initialise the hardware with the default polarities */
bcm2835_wr(bs, BCM2835_SPI_CS,
BCM2835_SPI_CS_CLEAR_RX | BCM2835_SPI_CS_CLEAR_TX);
@ -506,6 +803,8 @@ static int bcm2835_spi_remove(struct platform_device *pdev)
clk_disable_unprepare(bs->clk);
bcm2835_dma_release(master);
return 0;
}