spi: sh-msiof: Simplify calculation of divisors for transfer rate

The change updates sh_msiof_spi_set_clk_regs() function by iterating
over BRDV power values. Note that the change is a functional one, namely
prescaler output x 1/1 set in BRDV bit field (0b111) for MSO division
rate set to 2 is substituted by BRDV = 0b000 and BRPS = 0b0, in terms
of written values to TSCR setting of 0x0107 is substituted by 0x0000,
and for all input parameter cases this is the only functional change,
which touches the controller.

As a result of the rework the function is supposed to be slightly more
efficient and more readable and maintainable in case of any further
extensions.

Signed-off-by: Vladimir Zapolskiy <vladimir_zapolskiy@mentor.com>
Signed-off-by: Mark Brown <broonie@kernel.org>

drivers/spi/spi-sh-msiof.c

@@ -39,7 +39,7 @@ struct sh_msiof_chipdata {
 	u16 tx_fifo_size;
 	u16 rx_fifo_size;
 	u16 master_flags;
-	u16 min_div;
+	u16 min_div_pow;
 };
 
 struct sh_msiof_spi_priv {
@@ -51,7 +51,7 @@ struct sh_msiof_spi_priv {
 	struct completion done;
 	unsigned int tx_fifo_size;
 	unsigned int rx_fifo_size;
-	unsigned int min_div;
+	unsigned int min_div_pow;
 	void *tx_dma_page;
 	void *rx_dma_page;
 	dma_addr_t tx_dma_addr;
@@ -249,43 +249,46 @@ static irqreturn_t sh_msiof_spi_irq(int irq, void *data)
 	return IRQ_HANDLED;
 }
 
-static struct {
-	unsigned short div;
-	unsigned short brdv;
-} const sh_msiof_spi_div_table[] = {
-	{ 1,	SCR_BRDV_DIV_1 },
-	{ 2,	SCR_BRDV_DIV_2 },
-	{ 4,	SCR_BRDV_DIV_4 },
-	{ 8,	SCR_BRDV_DIV_8 },
-	{ 16,	SCR_BRDV_DIV_16 },
-	{ 32,	SCR_BRDV_DIV_32 },
+static const u32 sh_msiof_spi_div_array[] = {
+	SCR_BRDV_DIV_1, SCR_BRDV_DIV_2,	 SCR_BRDV_DIV_4,
+	SCR_BRDV_DIV_8,	SCR_BRDV_DIV_16, SCR_BRDV_DIV_32,
 };
 
 static void sh_msiof_spi_set_clk_regs(struct sh_msiof_spi_priv *p,
 				      unsigned long parent_rate, u32 spi_hz)
 {
-	unsigned long div = 1024;
+	unsigned long div;
 	u32 brps, scr;
-	size_t k;
+	unsigned int div_pow = p->min_div_pow;
 
-	if (!WARN_ON(!spi_hz || !parent_rate))
-		div = DIV_ROUND_UP(parent_rate, spi_hz);
-
-	div = max_t(unsigned long, div, p->min_div);
-
-	for (k = 0; k < ARRAY_SIZE(sh_msiof_spi_div_table); k++) {
-		brps = DIV_ROUND_UP(div, sh_msiof_spi_div_table[k].div);
-		/* SCR_BRDV_DIV_1 is valid only if BRPS is x 1/1 or x 1/2 */
-		if (sh_msiof_spi_div_table[k].div == 1 && brps > 2)
-			continue;
-		if (brps <= 32) /* max of brdv is 32 */
-			break;
+	if (!spi_hz || !parent_rate) {
+		WARN(1, "Invalid clock rate parameters %lu and %u\n",
+		     parent_rate, spi_hz);
+		return;
 	}
 
-	k = min_t(int, k, ARRAY_SIZE(sh_msiof_spi_div_table) - 1);
-	brps = min_t(int, brps, 32);
+	div = DIV_ROUND_UP(parent_rate, spi_hz);
+	if (div <= 1024) {
+		/* SCR_BRDV_DIV_1 is valid only if BRPS is x 1/1 or x 1/2 */
+		if (!div_pow && div <= 32 && div > 2)
+			div_pow = 1;
 
-	scr = sh_msiof_spi_div_table[k].brdv | SCR_BRPS(brps);
+		if (div_pow)
+			brps = (div + 1) >> div_pow;
+		else
+			brps = div;
+
+		for (; brps > 32; div_pow++)
+			brps = (brps + 1) >> 1;
+	} else {
+		/* Set transfer rate composite divisor to 2^5 * 32 = 1024 */
+		dev_err(&p->pdev->dev,
+			"Requested SPI transfer rate %d is too low\n", spi_hz);
+		div_pow = 5;
+		brps = 32;
+	}
+
+	scr = sh_msiof_spi_div_array[div_pow] | SCR_BRPS(brps);
 	sh_msiof_write(p, TSCR, scr);
 	if (!(p->master->flags & SPI_MASTER_MUST_TX))
 		sh_msiof_write(p, RSCR, scr);
@@ -1041,21 +1044,21 @@ static const struct sh_msiof_chipdata sh_data = {
 	.tx_fifo_size = 64,
 	.rx_fifo_size = 64,
 	.master_flags = 0,
-	.min_div = 1,
+	.min_div_pow = 0,
 };
 
 static const struct sh_msiof_chipdata rcar_gen2_data = {
 	.tx_fifo_size = 64,
 	.rx_fifo_size = 64,
 	.master_flags = SPI_MASTER_MUST_TX,
-	.min_div = 1,
+	.min_div_pow = 0,
 };
 
 static const struct sh_msiof_chipdata rcar_gen3_data = {
 	.tx_fifo_size = 64,
 	.rx_fifo_size = 64,
 	.master_flags = SPI_MASTER_MUST_TX,
-	.min_div = 2,
+	.min_div_pow = 1,
 };
 
 static const struct of_device_id sh_msiof_match[] = {
@@ -1319,7 +1322,7 @@ static int sh_msiof_spi_probe(struct platform_device *pdev)
 	platform_set_drvdata(pdev, p);
 	p->master = master;
 	p->info = info;
-	p->min_div = chipdata->min_div;
+	p->min_div_pow = chipdata->min_div_pow;
 
 	init_completion(&p->done);