spi: rzv2h-rspi: avoid recomputing transfer frequency

Renesas RZ/T2H (R9A09G077) and RZ/N2H (R9A09G087) SoCs have a more
complicated algorithm for calculating the optimal SPI transfer frequency
compared to RZ/V2H, as the clock from which the SPI frequency is
generated supports multiple dividers.

Cache the requested transfer frequency and skip calling
rzv2h_rspi_setup_clock() if it matches the last used one to prepare for
adding support for variable clock frequency handling.

Signed-off-by: Cosmin Tanislav <cosmin-gabriel.tanislav.xa@renesas.com>
Link: https://patch.msgid.link/20251119161434.595677-6-cosmin-gabriel.tanislav.xa@renesas.com
Signed-off-by: Mark Brown <broonie@kernel.org>

Author: Demon000

drivers/spi/spi-rzv2h-rspi.c

@@ -81,6 +81,7 @@ struct rzv2h_rspi_priv {
 	struct clk *tclk;
 	wait_queue_head_t wait;
 	unsigned int bytes_per_word;
+	u32 last_speed_hz;
 	u32 freq;
 	u16 status;
 	u8 spr;
@@ -298,9 +299,13 @@ static int rzv2h_rspi_prepare_message(struct spi_controller *ctlr,
 
 	rspi->bytes_per_word = roundup_pow_of_two(BITS_TO_BYTES(bits_per_word));
 
-	rspi->freq = rzv2h_rspi_setup_clock(rspi, speed_hz);
-	if (!rspi->freq)
-		return -EINVAL;
+	if (speed_hz != rspi->last_speed_hz) {
+		rspi->freq = rzv2h_rspi_setup_clock(rspi, speed_hz);
+		if (!rspi->freq)
+			return -EINVAL;
+
+		rspi->last_speed_hz = speed_hz;
+	}
 
 	writeb(rspi->spr, rspi->base + RSPI_SPBR);