From: Christophe Leroy christophe.leroy@csgroup.eu
commit fc96ec826bced75cc6b9c07a4ac44bbf651337ab upstream.
On CPM, the RISC core is a lot more efficiant when doing transfers in 16-bits chunks than in 8-bits chunks, but unfortunately the words need to be byte swapped as seen in a previous commit.
So, for large tranfers with an even size, allocate a temporary tx buffer and byte-swap data before and after transfer.
This change allows setting higher speed for transfer. For instance on an MPC 8xx (CPM1 comms RISC processor), the documentation tells that transfer in byte mode at 1 kbit/s uses 0.200% of CPM load at 25 MHz while a word transfer at the same speed uses 0.032% of CPM load. This means the speed can be 6 times higher in word mode for the same CPM load.
For the time being, only do it on CPM1 as there must be a trade-off between the CPM load reduction and the CPU load required to byte swap the data.
Signed-off-by: Christophe Leroy christophe.leroy@csgroup.eu Link: https://lore.kernel.org/r/f2e981f20f92dd28983c3949702a09248c23845c.168037180... Signed-off-by: Mark Brown broonie@kernel.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- drivers/spi/spi-fsl-cpm.c | 23 +++++++++++++++++++++++ drivers/spi/spi-fsl-spi.c | 3 +++ 2 files changed, 26 insertions(+)
--- a/drivers/spi/spi-fsl-cpm.c +++ b/drivers/spi/spi-fsl-cpm.c @@ -21,6 +21,7 @@ #include <linux/spi/spi.h> #include <linux/types.h> #include <linux/platform_device.h> +#include <linux/byteorder/generic.h>
#include "spi-fsl-cpm.h" #include "spi-fsl-lib.h" @@ -120,6 +121,21 @@ int fsl_spi_cpm_bufs(struct mpc8xxx_spi mspi->rx_dma = mspi->dma_dummy_rx; mspi->map_rx_dma = 0; } + if (t->bits_per_word == 16 && t->tx_buf) { + const u16 *src = t->tx_buf; + u16 *dst; + int i; + + dst = kmalloc(t->len, GFP_KERNEL); + if (!dst) + return -ENOMEM; + + for (i = 0; i < t->len >> 1; i++) + dst[i] = cpu_to_le16p(src + i); + + mspi->tx = dst; + mspi->map_tx_dma = 1; + }
if (mspi->map_tx_dma) { void *nonconst_tx = (void *)mspi->tx; /* shut up gcc */ @@ -173,6 +189,13 @@ void fsl_spi_cpm_bufs_complete(struct mp if (mspi->map_rx_dma) dma_unmap_single(dev, mspi->rx_dma, t->len, DMA_FROM_DEVICE); mspi->xfer_in_progress = NULL; + + if (t->bits_per_word == 16 && t->rx_buf) { + int i; + + for (i = 0; i < t->len; i += 2) + le16_to_cpus(t->rx_buf + i); + } } EXPORT_SYMBOL_GPL(fsl_spi_cpm_bufs_complete);
--- a/drivers/spi/spi-fsl-spi.c +++ b/drivers/spi/spi-fsl-spi.c @@ -351,6 +351,9 @@ static int fsl_spi_prepare_message(struc return -EINVAL; if (t->bits_per_word == 16 || t->bits_per_word == 32) t->bits_per_word = 8; /* pretend its 8 bits */ + if (t->bits_per_word == 8 && t->len >= 256 && + (mpc8xxx_spi->flags & SPI_CPM1)) + t->bits_per_word = 16; } } return fsl_spi_setup_transfer(m->spi, first);