spi: lpspi: Improve the stability of lpspi data transmission

Use SR_TDF to judge if need to send data, and SR_FCF is to judge if
transmission end and to replace the waiting after transmission end.
This waiting has no actual meaning, for module will set the FCF
flag at the real end.

The changes of interrupt flag and ISR function reduce the times of
calling ISR. The use of the FCF flag improves the stability of the
data transmission. These two points generally improve the data
transfer speed of lpspi, especially when it is set to slave mode
it can support higher transfer speed of the host.

After making these changes, there is no need to use
fsl_lpspi_txfifo_empty(), so remove it.
Signed-off-by: Clark Wang <xiaoning.wang@nxp.com>
Signed-off-by: Mark Brown <broonie@kernel.org>

drivers/spi/spi-fsl-lpspi.c

@@ -49,9 +49,11 @@
 #define CR_RST		BIT(1)
 #define CR_MEN		BIT(0)
 #define SR_TCF		BIT(10)
+#define SR_FCF		BIT(9)
 #define SR_RDF		BIT(1)
 #define SR_TDF		BIT(0)
 #define IER_TCIE	BIT(10)
+#define IER_FCIE	BIT(9)
 #define IER_RDIE	BIT(1)
 #define IER_TDIE	BIT(0)
 #define CFGR1_PCSCFG	BIT(27)
@@ -161,28 +163,10 @@ static int lpspi_unprepare_xfer_hardware(struct spi_controller *controller)
 	return 0;
 }
 
-static int fsl_lpspi_txfifo_empty(struct fsl_lpspi_data *fsl_lpspi)
-{
-	u32 txcnt;
-	unsigned long orig_jiffies = jiffies;
-
-	do {
-		txcnt = readl(fsl_lpspi->base + IMX7ULP_FSR) & 0xff;
-
-		if (time_after(jiffies, orig_jiffies + msecs_to_jiffies(500))) {
-			dev_dbg(fsl_lpspi->dev, "txfifo empty timeout\n");
-			return -ETIMEDOUT;
-		}
-		cond_resched();
-
-	} while (txcnt);
-
-	return 0;
-}
-
 static void fsl_lpspi_write_tx_fifo(struct fsl_lpspi_data *fsl_lpspi)
 {
 	u8 txfifo_cnt;
+	u32 temp;
 
 	txfifo_cnt = readl(fsl_lpspi->base + IMX7ULP_FSR) & 0xff;
 
@@ -193,9 +177,15 @@ static void fsl_lpspi_write_tx_fifo(struct fsl_lpspi_data *fsl_lpspi)
 		txfifo_cnt++;
 	}
 
-	if (!fsl_lpspi->remain && (txfifo_cnt < fsl_lpspi->txfifosize))
-		writel(0, fsl_lpspi->base + IMX7ULP_TDR);
-	else
+	if (txfifo_cnt < fsl_lpspi->txfifosize) {
+		if (!fsl_lpspi->is_slave) {
+			temp = readl(fsl_lpspi->base + IMX7ULP_TCR);
+			temp &= ~TCR_CONTC;
+			writel(temp, fsl_lpspi->base + IMX7ULP_TCR);
+		}
+
+		fsl_lpspi_intctrl(fsl_lpspi, IER_FCIE);
+	} else
 		fsl_lpspi_intctrl(fsl_lpspi, IER_TDIE);
 }
 
@@ -391,12 +381,6 @@ static int fsl_lpspi_transfer_one(struct spi_controller *controller,
 	if (ret)
 		return ret;
 
-	ret = fsl_lpspi_txfifo_empty(fsl_lpspi);
-	if (ret)
-		return ret;
-
-	fsl_lpspi_read_rx_fifo(fsl_lpspi);
-
 	return 0;
 }
 
@@ -408,7 +392,6 @@ static int fsl_lpspi_transfer_one_msg(struct spi_controller *controller,
 	struct spi_device *spi = msg->spi;
 	struct spi_transfer *xfer;
 	bool is_first_xfer = true;
-	u32 temp;
 	int ret = 0;
 
 	msg->status = 0;
@@ -428,13 +411,6 @@ static int fsl_lpspi_transfer_one_msg(struct spi_controller *controller,
 	}
 
 complete:
-	if (!fsl_lpspi->is_slave) {
-		/* de-assert SS, then finalize current message */
-		temp = readl(fsl_lpspi->base + IMX7ULP_TCR);
-		temp &= ~TCR_CONTC;
-		writel(temp, fsl_lpspi->base + IMX7ULP_TCR);
-	}
-
 	msg->status = ret;
 	spi_finalize_current_message(controller);
 
@@ -443,20 +419,23 @@ static int fsl_lpspi_transfer_one_msg(struct spi_controller *controller,
 
 static irqreturn_t fsl_lpspi_isr(int irq, void *dev_id)
 {
+	u32 temp_SR, temp_IER;
 	struct fsl_lpspi_data *fsl_lpspi = dev_id;
-	u32 temp;
 
+	temp_IER = readl(fsl_lpspi->base + IMX7ULP_IER);
 	fsl_lpspi_intctrl(fsl_lpspi, 0);
-	temp = readl(fsl_lpspi->base + IMX7ULP_SR);
+	temp_SR = readl(fsl_lpspi->base + IMX7ULP_SR);
 
 	fsl_lpspi_read_rx_fifo(fsl_lpspi);
 
-	if (temp & SR_TDF) {
+	if ((temp_SR & SR_TDF) && (temp_IER & IER_TDIE)) {
 		fsl_lpspi_write_tx_fifo(fsl_lpspi);
+		return IRQ_HANDLED;
+	}
 
-		if (!fsl_lpspi->remain)
+	if (temp_SR & SR_FCF && (temp_IER & IER_FCIE)) {
+		writel(SR_FCF, fsl_lpspi->base + IMX7ULP_SR);
 			complete(&fsl_lpspi->xfer_done);
-
 		return IRQ_HANDLED;
 	}