spi: fsl-dspi: Avoid using -EINPROGRESS error code

Refactor dspi_rxtx() and dspi_poll() to not return -EINPROGRESS because
this isn't actually a status that is ever returned to the core layer but
some internal state. Use true/false return value on dspi_rxtx() for this
instead.

This will help separate internal vs external status for the later change
to store the external status directly in cur_msg->status.

No functional changes intended.

Co-developed-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Signed-off-by: James Clark <james.clark@linaro.org>
Reviewed-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Message-ID: <20250902-james-nxp-spi-dma-v6-1-f7aa2c5e56e2@linaro.org>
Signed-off-by: Mark Brown <broonie@kernel.org>

Author: james-c-linaro

drivers/spi/spi-fsl-dspi.c

@@ -986,36 +986,45 @@ static void dspi_fifo_write(struct fsl_dspi *dspi)
 				dspi->progress, !dspi->irq);
 }
 
-static int dspi_rxtx(struct fsl_dspi *dspi)
+/*
+ * Read the previous transfer from the FIFO and transmit the next one.
+ *
+ * Returns false if the buffer to be transmitted is empty, and true if there is
+ * still data to transmit.
+ */
+static bool dspi_rxtx(struct fsl_dspi *dspi)
 {
 	dspi_fifo_read(dspi);
 
 	if (!dspi->len)
 		/* Success! */
-		return 0;
+		return false;
 
 	dspi_fifo_write(dspi);
 
-	return -EINPROGRESS;
+	return true;
 }
 
 static int dspi_poll(struct fsl_dspi *dspi)
 {
-	int tries = 1000;
+	int tries;
+	int err = 0;
 	u32 spi_sr;
 
 	do {
-		regmap_read(dspi->regmap, SPI_SR, &spi_sr);
-		regmap_write(dspi->regmap, SPI_SR, spi_sr);
-
-		if (spi_sr & SPI_SR_CMDTCF)
+		for (tries = 1000; tries > 0; --tries) {
+			regmap_read(dspi->regmap, SPI_SR, &spi_sr);
+			regmap_write(dspi->regmap, SPI_SR, spi_sr);
+			if (spi_sr & SPI_SR_CMDTCF)
+				break;
+		}
+		if (!tries) {
+			err = -ETIMEDOUT;
 			break;
-	} while (--tries);
-
-	if (!tries)
-		return -ETIMEDOUT;
+		}
+	} while (dspi_rxtx(dspi));
 
-	return dspi_rxtx(dspi);
+	return err;
 }
 
 static irqreturn_t dspi_interrupt(int irq, void *dev_id)
@@ -1029,7 +1038,7 @@ static irqreturn_t dspi_interrupt(int irq, void *dev_id)
 	if (!(spi_sr & SPI_SR_CMDTCF))
 		return IRQ_NONE;
 
-	if (dspi_rxtx(dspi) == 0)
+	if (dspi_rxtx(dspi) == false)
 		complete(&dspi->xfer_done);
 
 	return IRQ_HANDLED;
@@ -1137,9 +1146,7 @@ static int dspi_transfer_one_message(struct spi_controller *ctlr,
 			if (dspi->irq) {
 				wait_for_completion(&dspi->xfer_done);
 			} else {
-				do {
-					status = dspi_poll(dspi);
-				} while (status == -EINPROGRESS);
+				status = dspi_poll(dspi);
 			}
 		}
 		if (status)