spi: spi-zynqmp-gqspi: Avoid setting baud rate multiple times for same SPI frequency

During every transfer the GQSPI driver configures the baud rate value. But
when there is no change in the SPI clock frequency the driver should avoid
rewriting the same baud rate value to the configuration register. Update
GQSPI driver to rewrite the baud rate value if there is any change in SPI
clock frequency.
Signed-off-by: Amit Kumar Mahapatra <amit.kumar-mahapatra@amd.com>
Link: https://lore.kernel.org/r/20221011062040.12116-4-amit.kumar-mahapatra@amd.comSigned-off-by: Mark Brown <broonie@kernel.org>

drivers/spi/spi-zynqmp-gqspi.c

@@ -159,6 +159,7 @@ enum mode_type {GQSPI_MODE_IO, GQSPI_MODE_DMA};
  * @mode:		Defines the mode in which QSPI is operating
  * @data_completion:	completion structure
  * @op_lock:		Operational lock
+ * @speed_hz:          Current SPI bus clock speed in hz
  */
 struct zynqmp_qspi {
 	struct spi_controller *ctlr;
@@ -179,6 +180,7 @@ struct zynqmp_qspi {
 	enum mode_type mode;
 	struct completion data_completion;
 	struct mutex op_lock;
+	u32 speed_hz;
 };
 
 /**
@@ -273,7 +275,8 @@ static void zynqmp_gqspi_selectslave(struct zynqmp_qspi *instanceptr,
  */
 static void zynqmp_qspi_init_hw(struct zynqmp_qspi *xqspi)
 {
-	u32 config_reg;
+	u32 config_reg, baud_rate_val = 0;
+	ulong clk_rate;
 
 	/* Select the GQSPI mode */
 	zynqmp_gqspi_write(xqspi, GQSPI_SEL_OFST, GQSPI_SEL_MASK);
@@ -318,6 +321,16 @@ static void zynqmp_qspi_init_hw(struct zynqmp_qspi *xqspi)
 	else
 		config_reg &= ~GQSPI_CFG_CLK_POL_MASK;
 
+	/* Set the clock frequency */
+	clk_rate = clk_get_rate(xqspi->refclk);
+	while ((baud_rate_val < GQSPI_BAUD_DIV_MAX) &&
+	       (clk_rate /
+		(GQSPI_BAUD_DIV_SHIFT << baud_rate_val)) > xqspi->speed_hz)
+		baud_rate_val++;
+
+	config_reg &= ~GQSPI_CFG_BAUD_RATE_DIV_MASK;
+	config_reg |= (baud_rate_val << GQSPI_CFG_BAUD_RATE_DIV_SHIFT);
+
 	zynqmp_gqspi_write(xqspi, GQSPI_CONFIG_OFST, config_reg);
 
 	/* Clear the TX and RX FIFO */
@@ -466,22 +479,29 @@ static int zynqmp_qspi_config_op(struct zynqmp_qspi *xqspi,
 				 struct spi_device *qspi)
 {
 	ulong clk_rate;
-	u32 config_reg, baud_rate_val = 0;
+	u32 config_reg, req_speed_hz, baud_rate_val = 0;
 
-	/* Set the clock frequency */
-	/* If req_hz == 0, default to lowest speed */
-	clk_rate = clk_get_rate(xqspi->refclk);
+	req_speed_hz = qspi->max_speed_hz;
 
-	while ((baud_rate_val < GQSPI_BAUD_DIV_MAX) &&
-	       (clk_rate /
-		(GQSPI_BAUD_DIV_SHIFT << baud_rate_val)) > qspi->max_speed_hz)
-		baud_rate_val++;
+	if (xqspi->speed_hz != req_speed_hz) {
+		xqspi->speed_hz = req_speed_hz;
 
-	config_reg = zynqmp_gqspi_read(xqspi, GQSPI_CONFIG_OFST);
+		/* Set the clock frequency */
+		/* If req_speed_hz == 0, default to lowest speed */
+		clk_rate = clk_get_rate(xqspi->refclk);
 
-	config_reg &= ~GQSPI_CFG_BAUD_RATE_DIV_MASK;
-	config_reg |= (baud_rate_val << GQSPI_CFG_BAUD_RATE_DIV_SHIFT);
-	zynqmp_gqspi_write(xqspi, GQSPI_CONFIG_OFST, config_reg);
+		while ((baud_rate_val < GQSPI_BAUD_DIV_MAX) &&
+		       (clk_rate /
+			(GQSPI_BAUD_DIV_SHIFT << baud_rate_val)) >
+		       req_speed_hz)
+			baud_rate_val++;
+
+		config_reg = zynqmp_gqspi_read(xqspi, GQSPI_CONFIG_OFST);
+
+		config_reg &= ~GQSPI_CFG_BAUD_RATE_DIV_MASK;
+		config_reg |= (baud_rate_val << GQSPI_CFG_BAUD_RATE_DIV_SHIFT);
+		zynqmp_gqspi_write(xqspi, GQSPI_CONFIG_OFST, config_reg);
+	}
 	return 0;
 }
 
@@ -1173,6 +1193,8 @@ static int zynqmp_qspi_probe(struct platform_device *pdev)
 
 	ctlr->mode_bits = SPI_CPOL | SPI_CPHA | SPI_RX_DUAL | SPI_RX_QUAD |
 		SPI_TX_DUAL | SPI_TX_QUAD;
+	ctlr->max_speed_hz = clk_get_rate(xqspi->refclk) / 2;
+	xqspi->speed_hz = ctlr->max_speed_hz;
 
 	/* QSPI controller initializations */
 	zynqmp_qspi_init_hw(xqspi);
@@ -1209,7 +1231,6 @@ static int zynqmp_qspi_probe(struct platform_device *pdev)
 	ctlr->bits_per_word_mask = SPI_BPW_MASK(8);
 	ctlr->mem_ops = &zynqmp_qspi_mem_ops;
 	ctlr->setup = zynqmp_qspi_setup_op;
-	ctlr->max_speed_hz = clk_get_rate(xqspi->refclk) / 2;
 	ctlr->bits_per_word_mask = SPI_BPW_MASK(8);
 	ctlr->dev.of_node = np;
 	ctlr->auto_runtime_pm = true;