spi: fsl-cpm: Use 16 bit mode for large transfers with even size

(cherry picked from upstream fc96ec826bced75cc6b9c07a4ac44bbf651337ab)

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.1680371809.git.christophe.leroy@csgroup.eu
Signed-off-by: Mark Brown <broonie@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/spi/spi-fsl-cpm.c b/drivers/spi/spi-fsl-cpm.c
index 858f0544289e6a7211c2e85fc1d82672923401a7..c7079a9cd577f658e77d31d3650b2fa5b76bbe87 100644 (file)
--- 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,
                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 mpc8xxx_spi *mspi)
        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);
 

diff --git a/drivers/spi/spi-fsl-spi.c b/drivers/spi/spi-fsl-spi.c
index a974074b253af600c39a22a1626723d56f14f7de..8006759c1a0c637e71971f7c148a3e155811a700 100644 (file)
--- a/drivers/spi/spi-fsl-spi.c
+++ b/drivers/spi/spi-fsl-spi.c
@@ -369,6 +369,9 @@ static int fsl_spi_do_one_msg(struct spi_master *master,
                                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;
                }
        }