[PATCH 2/5] spi: imx: Use dynamic bursts only when bits_per_word is 8, 16 or 32

From: Maxime Chevallier
Date: Tue Jul 17 2018 - 09:43:34 EST


The dynamic bursts mode allows to group together multiple words into a
single burst. To do so, it's necessary that words can be packed into the
32-bits FIFO entries, so we can't allow using this mode with bit_per_words
different to 8, 16 or 32.

This prevents shitfing out extra clock ticks for transfers with
bit_per_word values not aligned on 8 bits.

With that , we are sure that only the correct number of bits is
shifted out at each transfer, so we don't need to mask out the remaining
parts of the words.

Signed-off-by: Maxime Chevallier <maxime.chevallier@xxxxxxxxxxx>
---
drivers/spi/spi-imx.c | 23 +++++++++--------------
1 file changed, 9 insertions(+), 14 deletions(-)

diff --git a/drivers/spi/spi-imx.c b/drivers/spi/spi-imx.c
index d75153c995af..ecafbda5ec94 100644
--- a/drivers/spi/spi-imx.c
+++ b/drivers/spi/spi-imx.c
@@ -95,7 +95,6 @@ struct spi_imx_data {
const void *tx_buf;
unsigned int txfifo; /* number of words pushed in tx FIFO */
unsigned int dynamic_burst, read_u32;
- unsigned int word_mask;

/* Slave mode */
bool slave_mode;
@@ -291,7 +290,6 @@ static void spi_imx_buf_rx_swap_u32(struct spi_imx_data *spi_imx)
else if (bytes_per_word == 2)
val = (val << 16) | (val >> 16);
#endif
- val &= spi_imx->word_mask;
*(u32 *)spi_imx->rx_buf = val;
spi_imx->rx_buf += sizeof(u32);
}
@@ -322,7 +320,6 @@ static void spi_imx_buf_tx_swap_u32(struct spi_imx_data *spi_imx)

if (spi_imx->tx_buf) {
val = *(u32 *)spi_imx->tx_buf;
- val &= spi_imx->word_mask;
spi_imx->tx_buf += sizeof(u32);
}

@@ -1102,25 +1099,23 @@ static int spi_imx_setupxfer(struct spi_device *spi,
spi_imx->bits_per_word = t->bits_per_word;
spi_imx->speed_hz = t->speed_hz;

- /* Initialize the functions for transfer */
- if (spi_imx->devtype_data->dynamic_burst && !spi_imx->slave_mode) {
- u32 mask;
+ /*
+ * Initialize the functions for transfer. To transfer non byte-aligned
+ * words, we have to use multiple word-size bursts, we can't use
+ * dynamic_burst in that case.
+ */
+ if (spi_imx->devtype_data->dynamic_burst && !spi_imx->slave_mode &&
+ (spi_imx->bits_per_word == 8 ||
+ spi_imx->bits_per_word == 16 ||
+ spi_imx->bits_per_word == 32)) {

spi_imx->read_u32 = 1;

- mask = (1 << spi_imx->bits_per_word) - 1;
spi_imx->rx = spi_imx_buf_rx_swap;
spi_imx->tx = spi_imx_buf_tx_swap;
spi_imx->dynamic_burst = 1;
spi_imx->remainder = t->len;

- if (spi_imx->bits_per_word <= 8)
- spi_imx->word_mask = mask << 24 | mask << 16
- | mask << 8 | mask;
- else if (spi_imx->bits_per_word <= 16)
- spi_imx->word_mask = mask << 16 | mask;
- else
- spi_imx->word_mask = mask;
} else {
if (spi_imx->bits_per_word <= 8) {
spi_imx->rx = spi_imx_buf_rx_u8;
--
2.11.0