spi: dw: fix multiple slaves with different baudrates

Add current master clock to dws struct and compare it against the
requestedtransfer speed. Update clock divider only if necessary.
Signed-off-by: Matthias Seidel <kernel@mseidel.net>
Signed-off-by: Mark Brown <broonie@kernel.org>

drivers/spi/spi-dw.c

@@ -283,7 +283,6 @@ static int dw_spi_transfer_one(struct spi_master *master,
 	struct chip_data *chip = spi_get_ctldata(spi);
 	u8 imask = 0;
 	u16 txlevel = 0;
-	u16 clk_div;
 	u32 cr0;
 	int ret;
 
@@ -298,13 +297,13 @@ static int dw_spi_transfer_one(struct spi_master *master,
 	spi_enable_chip(dws, 0);
 
 	/* Handle per transfer options for bpw and speed */
+	if (transfer->speed_hz != dws->current_freq) {
 		if (transfer->speed_hz != chip->speed_hz) {
 			/* clk_div doesn't support odd number */
-		clk_div = (dws->max_freq / transfer->speed_hz + 1) & 0xfffe;
-
+			chip->clk_div = (dws->max_freq / transfer->speed_hz + 1) & 0xfffe;
 			chip->speed_hz = transfer->speed_hz;
-		chip->clk_div = clk_div;
-
+		}
+		dws->current_freq = transfer->speed_hz;
 		spi_set_clk(dws, chip->clk_div);
 	}
 	if (transfer->bits_per_word == 8) {

drivers/spi/spi-dw.h

@@ -123,6 +123,7 @@ struct dw_spi {
 	u8			n_bytes;	/* current is a 1/2 bytes op */
 	u32			dma_width;
 	irqreturn_t		(*transfer_handler)(struct dw_spi *dws);
+	u32			current_freq;	/* frequency in hz */
 
 	/* DMA info */
 	int			dma_inited;