spi: rzv2h-rspi: add support for variable transfer clock

The Renesas RZ/T2H (R9A09G077) and RZ/N2H (R9A09G087) SoCs have a more
complicated clocking setup for the SPI transfer clock than RZ/V2H, as
the clock from which it is generated supports multiple dividers.

To prepare for adding support for these SoCs, do the following changes.

Use the minimum frequency of SPI clock to calculate the SPI
controller's min_speed_hz, and the maximum frequency to calculate
max_speed_hz.

Apply the clock rate found by the .find_tclk_rate() to the found clock.

Signed-off-by: Cosmin Tanislav <cosmin-gabriel.tanislav.xa@renesas.com>
Link: https://patch.msgid.link/20251119161434.595677-9-cosmin-gabriel.tanislav.xa@renesas.com
Signed-off-by: Mark Brown <broonie@kernel.org>

Author: Demon000

drivers/spi/spi-rzv2h-rspi.c

@@ -308,6 +308,7 @@ static u32 rzv2h_rspi_setup_clock(struct rzv2h_rspi_priv *rspi, u32 hz)
 	struct rzv2h_rspi_best_clock best_clock = {
 		.error = ULONG_MAX,
 	};
+	int ret;
 
 	rspi->info->find_tclk_rate(rspi->tclk, hz, RSPI_SPBR_SPR_MIN,
 				   RSPI_SPBR_SPR_MAX, &best_clock);
@@ -323,6 +324,10 @@ static u32 rzv2h_rspi_setup_clock(struct rzv2h_rspi_priv *rspi, u32 hz)
 	if (!best_clock.clk_rate)
 		return -EINVAL;
 
+	ret = clk_set_rate(best_clock.clk, best_clock.clk_rate);
+	if (ret)
+		return 0;
+
 	rspi->use_pclk = best_clock.clk == rspi->pclk;
 	rspi->spr = best_clock.spr;
 	rspi->brdv = best_clock.brdv;
@@ -426,8 +431,8 @@ static int rzv2h_rspi_probe(struct platform_device *pdev)
 	struct device *dev = &pdev->dev;
 	struct rzv2h_rspi_priv *rspi;
 	struct clk_bulk_data *clks;
-	unsigned long tclk_rate;
 	int irq_rx, ret, i;
+	long tclk_rate;
 
 	controller = devm_spi_alloc_host(dev, sizeof(*rspi));
 	if (!controller)
@@ -460,8 +465,6 @@ static int rzv2h_rspi_probe(struct platform_device *pdev)
 	if (!rspi->tclk)
 		return dev_err_probe(dev, -EINVAL, "Failed to get tclk\n");
 
-	tclk_rate = clk_get_rate(rspi->tclk);
-
 	rspi->resets[0].id = "presetn";
 	rspi->resets[1].id = "tresetn";
 	ret = devm_reset_control_bulk_get_optional_exclusive(dev, RSPI_RESET_NUM,
@@ -493,9 +496,23 @@ static int rzv2h_rspi_probe(struct platform_device *pdev)
 	controller->unprepare_message = rzv2h_rspi_unprepare_message;
 	controller->num_chipselect = 4;
 	controller->transfer_one = rzv2h_rspi_transfer_one;
+
+	tclk_rate = clk_round_rate(rspi->tclk, 0);
+	if (tclk_rate < 0) {
+		ret = tclk_rate;
+		goto quit_resets;
+	}
+
 	controller->min_speed_hz = rzv2h_rspi_calc_bitrate(tclk_rate,
 							   RSPI_SPBR_SPR_MAX,
 							   RSPI_SPCMD_BRDV_MAX);
+
+	tclk_rate = clk_round_rate(rspi->tclk, ULONG_MAX);
+	if (tclk_rate < 0) {
+		ret = tclk_rate;
+		goto quit_resets;
+	}
+
 	controller->max_speed_hz = rzv2h_rspi_calc_bitrate(tclk_rate,
 							   RSPI_SPBR_SPR_MIN,
 							   RSPI_SPCMD_BRDV_MIN);