spi: axi-spi-engine: remove spi_engine_get_clk_div()

Now that host->max_speed_hz and xfer->effective_speed_hz are properly
set, we can use them instead of having to do more complex calculations
to get the clock divider for each transfer.

This removes the spi_engine_get_clk_div() function and replaces it with
just dividing the two clock rates. Since the hardware register value is
the divider minus one, we need to subtract one. Subtracting one was
previously done in the spi_engine_get_clk_div() function.

Signed-off-by: David Lechner <dlechner@baylibre.com>
Acked-by: Michael Hennerich <michael.hennerich@analog.com>
Acked-by: Nuno Sa <nuno.sa@analog.com>
Link: https://lore.kernel.org/r/20231204-axi-spi-engine-series-2-v1-3-063672323fce@baylibre.com
Signed-off-by: Mark Brown <broonie@kernel.org>

Author: dlech

drivers/spi/spi-axi-spi-engine.c

@@ -140,21 +140,6 @@ static unsigned int spi_engine_get_config(struct spi_device *spi)
 	return config;
 }
 
-static unsigned int spi_engine_get_clk_div(struct spi_engine *spi_engine,
-	struct spi_device *spi, struct spi_transfer *xfer)
-{
-	unsigned int clk_div;
-
-	clk_div = DIV_ROUND_UP(clk_get_rate(spi_engine->ref_clk),
-		xfer->speed_hz * 2);
-	if (clk_div > 255)
-		clk_div = 255;
-	else if (clk_div > 0)
-		clk_div -= 1;
-
-	return clk_div;
-}
-
 static void spi_engine_gen_xfer(struct spi_engine_program *p, bool dry,
 	struct spi_transfer *xfer)
 {
@@ -243,6 +228,7 @@ static void spi_engine_compile_message(struct spi_engine *spi_engine,
 	struct spi_message *msg, bool dry, struct spi_engine_program *p)
 {
 	struct spi_device *spi = msg->spi;
+	struct spi_controller *host = spi->controller;
 	struct spi_transfer *xfer;
 	int clk_div, new_clk_div;
 	bool keep_cs = false;
@@ -258,12 +244,13 @@ static void spi_engine_compile_message(struct spi_engine *spi_engine,
 	spi_engine_gen_cs(p, dry, spi, !xfer->cs_off);
 
 	list_for_each_entry(xfer, &msg->transfers, transfer_list) {
-		new_clk_div = spi_engine_get_clk_div(spi_engine, spi, xfer);
+		new_clk_div = host->max_speed_hz / xfer->effective_speed_hz;
 		if (new_clk_div != clk_div) {
 			clk_div = new_clk_div;
+			/* actual divider used is register value + 1 */
 			spi_engine_program_add_cmd(p, dry,
 				SPI_ENGINE_CMD_WRITE(SPI_ENGINE_CMD_REG_CLK_DIV,
-					clk_div));
+					clk_div - 1));
 		}
 
 		if (bits_per_word != xfer->bits_per_word) {
@@ -274,7 +261,7 @@ static void spi_engine_compile_message(struct spi_engine *spi_engine,
 		}
 
 		spi_engine_gen_xfer(p, dry, xfer);
-		spi_engine_gen_sleep(p, dry, spi_engine, clk_div, xfer);
+		spi_engine_gen_sleep(p, dry, spi_engine, clk_div - 1, xfer);
 
 		if (xfer->cs_change) {
 			if (list_is_last(&xfer->transfer_list, &msg->transfers)) {