spi: bcm2835: support effective_speed_hz

Setting spi_transfer->effective_speed_hz in transfer_one so that
it can get used in cs_change_delay configured with delay as a muliple
of SPI clock cycles.
Signed-off-by: Martin Sperl <kernel@martin.sperl.org>
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>
Link: https://lore.kernel.org/r/20200709074120.110069-2-mkl@pengutronix.deSigned-off-by: Mark Brown <broonie@kernel.org>

drivers/spi/spi-bcm2835.c

@@ -1082,7 +1082,7 @@ static int bcm2835_spi_transfer_one(struct spi_controller *ctlr,
 				    struct spi_transfer *tfr)
 {
 	struct bcm2835_spi *bs = spi_controller_get_devdata(ctlr);
-	unsigned long spi_hz, clk_hz, cdiv, spi_used_hz;
+	unsigned long spi_hz, clk_hz, cdiv;
 	unsigned long hz_per_byte, byte_limit;
 	u32 cs = bs->prepare_cs[spi->chip_select];
 
@@ -1102,7 +1102,7 @@ static int bcm2835_spi_transfer_one(struct spi_controller *ctlr,
 	} else {
 		cdiv = 0; /* 0 is the slowest we can go */
 	}
-	spi_used_hz = cdiv ? (clk_hz / cdiv) : (clk_hz / 65536);
+	tfr->effective_speed_hz = cdiv ? (clk_hz / cdiv) : (clk_hz / 65536);
 	bcm2835_wr(bs, BCM2835_SPI_CLK, cdiv);
 
 	/* handle all the 3-wire mode */
@@ -1122,7 +1122,7 @@ static int bcm2835_spi_transfer_one(struct spi_controller *ctlr,
 	 * per 300,000 Hz of bus clock.
 	 */
 	hz_per_byte = polling_limit_us ? (9 * 1000000) / polling_limit_us : 0;
-	byte_limit = hz_per_byte ? spi_used_hz / hz_per_byte : 1;
+	byte_limit = hz_per_byte ? tfr->effective_speed_hz / hz_per_byte : 1;
 
 	/* run in polling mode for short transfers */
 	if (tfr->len < byte_limit)