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spi: spi-ti-qspi: Use bounce buffer if read buffer is not DMA'ble 

Flash filesystems like JFFS2, UBIFS and MTD block layer can provide
vmalloc'd or kmap'd buffers that cannot be mapped using dma_map_sg() and
can potentially be in memory region above 32bit addressable region(ie
buffers belonging to memory region backed by LPAE) of DMA, implement
spi_flash_can_dma() interface to inform SPI core not to map such
buffers.
When buffers are not mapped for DMA, then use a pre allocated bounce
buffer(64K = typical flash erase sector size) to read from flash and
then do a copy to actual destination buffer. This is approach is much
faster than using memcpy using CPU and also reduces CPU load.

With this patch, UBIFS read speed is ~18MB/s and CPU utilization <20% on
DRA74 Rev H EVM. Performance degradation is negligible when compared
with non bounce buffer case while using UBIFS.

Signed-off-by: Vignesh R <vigneshr@ti.com>
Signed-off-by: Mark Brown <broonie@kernel.org>
This commit is contained in:
Vignesh R 2017-04-11 17:22:25 +05:30 committed by Mark Brown
parent 2bca34455b
commit c687c46e9e
1 changed files with 59 additions and 7 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

66
drivers/spi/spi-ti-qspi.c
View File

@ -33,6 +33,7 @@
#include <linux/pinctrl/consumer.h>
#include <linux/mfd/syscon.h>
#include <linux/regmap.h>
#include <linux/sizes.h>
#include <linux/spi/spi.h>
@ -57,6 +58,8 @@ struct ti_qspi {
struct ti_qspi_regs ctx_reg;
dma_addr_t mmap_phys_base;
dma_addr_t rx_bb_dma_addr;
void *rx_bb_addr;
struct dma_chan *rx_chan;
u32 spi_max_frequency;
@ -126,6 +129,8 @@ struct ti_qspi {
#define QSPI_SETUP_ADDR_SHIFT 8
#define QSPI_SETUP_DUMMY_SHIFT 10
#define QSPI_DMA_BUFFER_SIZE SZ_64K
static inline unsigned long ti_qspi_read(struct ti_qspi *qspi,
unsigned long reg)
{
@ -429,6 +434,35 @@ static int ti_qspi_dma_xfer(struct ti_qspi *qspi, dma_addr_t dma_dst,
return 0;
}
static int ti_qspi_dma_bounce_buffer(struct ti_qspi *qspi,
struct spi_flash_read_message *msg)
{
size_t readsize = msg->len;
void *to = msg->buf;
dma_addr_t dma_src = qspi->mmap_phys_base + msg->from;
int ret = 0;
/*
* Use bounce buffer as FS like jffs2, ubifs may pass
* buffers that does not belong to kernel lowmem region.
*/
while (readsize != 0) {
size_t xfer_len = min_t(size_t, QSPI_DMA_BUFFER_SIZE,
readsize);
ret = ti_qspi_dma_xfer(qspi, qspi->rx_bb_dma_addr,
dma_src, xfer_len);
if (ret != 0)
return ret;
memcpy(to, qspi->rx_bb_addr, xfer_len);
readsize -= xfer_len;
dma_src += xfer_len;
to += xfer_len;
}
return ret;
}
static int ti_qspi_dma_xfer_sg(struct ti_qspi *qspi, struct sg_table rx_sg,
loff_t from)
{
@ -496,6 +530,12 @@ static void ti_qspi_setup_mmap_read(struct spi_device *spi,
QSPI_SPI_SETUP_REG(spi->chip_select));
}
static bool ti_qspi_spi_flash_can_dma(struct spi_device *spi,
struct spi_flash_read_message *msg)
{
return virt_addr_valid(msg->buf);
}
static int ti_qspi_spi_flash_read(struct spi_device *spi,
struct spi_flash_read_message *msg)
{
@ -509,15 +549,12 @@ static int ti_qspi_spi_flash_read(struct spi_device *spi,
ti_qspi_setup_mmap_read(spi, msg);
if (qspi->rx_chan) {
if (msg->cur_msg_mapped) {
if (msg->cur_msg_mapped)
ret = ti_qspi_dma_xfer_sg(qspi, msg->rx_sg, msg->from);
if (ret)
goto err_unlock;
} else {
dev_err(qspi->dev, "Invalid address for DMA\n");
ret = -EIO;
else
ret = ti_qspi_dma_bounce_buffer(qspi, msg);
if (ret)
goto err_unlock;
}
} else {
memcpy_fromio(msg->buf, qspi->mmap_base + msg->from, msg->len);
}
@ -718,6 +755,17 @@ static int ti_qspi_probe(struct platform_device *pdev)
ret = 0;
goto no_dma;
}
qspi->rx_bb_addr = dma_alloc_coherent(qspi->dev,
QSPI_DMA_BUFFER_SIZE,
&qspi->rx_bb_dma_addr,
GFP_KERNEL | GFP_DMA);
if (!qspi->rx_bb_addr) {
dev_err(qspi->dev,
"dma_alloc_coherent failed, using PIO mode\n");
dma_release_channel(qspi->rx_chan);
goto no_dma;
}
master->spi_flash_can_dma = ti_qspi_spi_flash_can_dma;
master->dma_rx = qspi->rx_chan;
init_completion(&qspi->transfer_complete);
if (res_mmap)
@ -757,6 +805,10 @@ static int ti_qspi_remove(struct platform_device *pdev)
pm_runtime_put_sync(&pdev->dev);
pm_runtime_disable(&pdev->dev);
if (qspi->rx_bb_addr)
dma_free_coherent(qspi->dev, QSPI_DMA_BUFFER_SIZE,
qspi->rx_bb_addr,
qspi->rx_bb_dma_addr);
if (qspi->rx_chan)
dma_release_channel(qspi->rx_chan);