spi: sh-msiof: Reduce the number of times write to and perform the transmission from FIFO

The current state of the spi-sh-msiof, in master transfer mode: if t-> bits_per_word <= 8,
if the data length is divisible by 4 ((len & 3) = 0), the length of each word will be 32 bits
In case of data length can not be divisible by 4 ((len & 3) != 0), always set each word to be
8 bits, this will increase the number of times that write to FIFO, increasing the number of
times it should be transmitted. Assume that the number of bytes of data length more than 64 bytes,
each transmission will write 64 times into the TFDR then transmit, a maximum one-time
transmission will transmit 64 bytes if each word is 8 bits long.

Switch to setting if t->bits_per_word <= 8, the word length will be 32 bits although the data
length is not divisible by 4, then if leftover, will transmit the balance and the length of each
words is 1 byte. The maximum each can transmit up to 64 x 4 (Data Size = 32 bits (4 bytes)) = 256 bytes.
TMDR2 : Bits 28 to 24  BITLEN1[4:0] Data Size (8 to 32 bits)
        Bits 23 to 16  WDLEN1[7:0]  Word Count (1 to 64 words)

Signed-off-by: Hoan Nguyen An <na-hoan@jinso.co.jp>
Signed-off-by: Mark Brown <broonie@kernel.org>

1 files changed, 9 insertions, 1 deletions

diff --git a/drivers/spi/spi-sh-msiof.c b/drivers/spi/spi-sh-msiof.c
index d495d8604397..d14b407cc800 100644
--- a/drivers/spi/spi-sh-msiof.c
+++ b/drivers/spi/spi-sh-msiof.c
@@ -977,7 +977,7 @@ static int sh_msiof_transfer_one(struct spi_master *master,
 			return 0;
 	}
 
-	if (bits <= 8 && len > 15 && !(len & 3)) {
+	if (bits <= 8 && len > 15) {
 		bits = 32;
 		swab = true;
 	} else {
@@ -1038,6 +1038,14 @@ static int sh_msiof_transfer_one(struct spi_master *master,
 		if (rx_buf)
 			rx_buf += n * bytes_per_word;
 		words -= n;
+
+		if (words == 0 && (len % bytes_per_word)) {
+			words = len % bytes_per_word;
+			bits = t->bits_per_word;
+			bytes_per_word = 1;
+			tx_fifo = sh_msiof_spi_write_fifo_8;
+			rx_fifo = sh_msiof_spi_read_fifo_8;
+		}
 	}
 
 	return 0;