spi: sirf: decrease the interrupt count and latency of PIO mode

current PIO tranfer method be described as follows:
1. fill as much as bytes but no more than 256 bytes(fifo size)
2. enable oflow/uflow/txfifo_empty interrupt
3. isr process 3 interrupt signal, do complete works.
4. after isr done, if there are left bytes go into 1 else go into 5
5. transfer end

by current PIO transfer method:
1. reduce interrupt counts in spi interrupt line.
2. reduce interrupt latency because no do data fill/fetch in isr.

Signed-off-by: Qipan Li <Qipan.Li@csr.com>
Signed-off-by: Barry Song <Baohua.Song@csr.com>
Signed-off-by: Mark Brown <broonie@linaro.org>

drivers/spi/spi-sirf.c

@@ -86,6 +86,7 @@
 #define SIRFSOC_SPI_TX_DONE		BIT(1)
 #define SIRFSOC_SPI_RX_OFLOW		BIT(2)
 #define SIRFSOC_SPI_TX_UFLOW		BIT(3)
+#define SIRFSOC_SPI_RX_IO_DMA		BIT(4)
 #define SIRFSOC_SPI_RX_FIFO_FULL	BIT(6)
 #define SIRFSOC_SPI_TXFIFO_EMPTY	BIT(7)
 #define SIRFSOC_SPI_RXFIFO_THD_REACH	BIT(8)
@@ -265,41 +266,34 @@ static irqreturn_t spi_sirfsoc_irq(int irq, void *dev_id)
 {
 	struct sirfsoc_spi *sspi = dev_id;
 	u32 spi_stat = readl(sspi->base + SIRFSOC_SPI_INT_STATUS);
-
-	writel(spi_stat, sspi->base + SIRFSOC_SPI_INT_STATUS);
-
 	if (sspi->tx_by_cmd && (spi_stat & SIRFSOC_SPI_FRM_END)) {
 		complete(&sspi->tx_done);
 		writel(0x0, sspi->base + SIRFSOC_SPI_INT_EN);
+		writel(SIRFSOC_SPI_INT_MASK_ALL,
+				sspi->base + SIRFSOC_SPI_INT_STATUS);
 		return IRQ_HANDLED;
 	}
 
 	/* Error Conditions */
 	if (spi_stat & SIRFSOC_SPI_RX_OFLOW ||
 			spi_stat & SIRFSOC_SPI_TX_UFLOW) {
+		complete(&sspi->tx_done);
 		complete(&sspi->rx_done);
 		writel(0x0, sspi->base + SIRFSOC_SPI_INT_EN);
+		writel(SIRFSOC_SPI_INT_MASK_ALL,
+				sspi->base + SIRFSOC_SPI_INT_STATUS);
+		return IRQ_HANDLED;
 	}
+	if (spi_stat & SIRFSOC_SPI_TXFIFO_EMPTY)
+		complete(&sspi->tx_done);
+	while (!(readl(sspi->base + SIRFSOC_SPI_INT_STATUS) &
+		SIRFSOC_SPI_RX_IO_DMA))
+		cpu_relax();
+	complete(&sspi->rx_done);
+	writel(0x0, sspi->base + SIRFSOC_SPI_INT_EN);
+	writel(SIRFSOC_SPI_INT_MASK_ALL,
+			sspi->base + SIRFSOC_SPI_INT_STATUS);
 
-	if (spi_stat & (SIRFSOC_SPI_FRM_END
-			| SIRFSOC_SPI_RXFIFO_THD_REACH))
-		while (!((readl(sspi->base + SIRFSOC_SPI_RXFIFO_STATUS)
-				& SIRFSOC_SPI_FIFO_EMPTY)) &&
-				sspi->left_rx_word)
-			sspi->rx_word(sspi);
-
-	if (spi_stat & (SIRFSOC_SPI_TXFIFO_EMPTY |
-			SIRFSOC_SPI_TXFIFO_THD_REACH))
-		while (!((readl(sspi->base + SIRFSOC_SPI_TXFIFO_STATUS)
-				& SIRFSOC_SPI_FIFO_FULL)) &&
-				sspi->left_tx_word)
-			sspi->tx_word(sspi);
-
-	/* Received all words */
-	if ((sspi->left_rx_word == 0) && (sspi->left_tx_word == 0)) {
-		complete(&sspi->rx_done);
-		writel(0x0, sspi->base + SIRFSOC_SPI_INT_EN);
-	}
 	return IRQ_HANDLED;
 }
 
@@ -420,32 +414,45 @@ static void spi_sirfsoc_pio_transfer(struct spi_device *spi,
 	int timeout = t->len * 10;
 
 	sspi = spi_master_get_devdata(spi->master);
-	writel(SIRFSOC_SPI_FIFO_RESET, sspi->base + SIRFSOC_SPI_RXFIFO_OP);
-	writel(SIRFSOC_SPI_FIFO_RESET, sspi->base + SIRFSOC_SPI_TXFIFO_OP);
-	writel(SIRFSOC_SPI_FIFO_START, sspi->base + SIRFSOC_SPI_RXFIFO_OP);
-	writel(SIRFSOC_SPI_FIFO_START, sspi->base + SIRFSOC_SPI_TXFIFO_OP);
-	writel(0, sspi->base + SIRFSOC_SPI_INT_EN);
-	writel(SIRFSOC_SPI_INT_MASK_ALL, sspi->base + SIRFSOC_SPI_INT_STATUS);
-	writel(readl(sspi->base + SIRFSOC_SPI_CTRL) | SIRFSOC_SPI_MUL_DAT_MODE |
-		SIRFSOC_SPI_ENA_AUTO_CLR, sspi->base + SIRFSOC_SPI_CTRL);
-	writel(sspi->left_tx_word - 1,
-			sspi->base + SIRFSOC_SPI_TX_DMA_IO_LEN);
-	writel(sspi->left_rx_word - 1,
-			sspi->base + SIRFSOC_SPI_RX_DMA_IO_LEN);
-	sspi->tx_word(sspi);
-	writel(SIRFSOC_SPI_TXFIFO_EMPTY_INT_EN | SIRFSOC_SPI_TX_UFLOW_INT_EN |
-		SIRFSOC_SPI_RX_OFLOW_INT_EN | SIRFSOC_SPI_RXFIFO_THD_INT_EN |
-		SIRFSOC_SPI_TXFIFO_THD_INT_EN | SIRFSOC_SPI_FRM_END_INT_EN|
-		SIRFSOC_SPI_RXFIFO_FULL_INT_EN,
-		sspi->base + SIRFSOC_SPI_INT_EN);
-	writel(SIRFSOC_SPI_RX_EN | SIRFSOC_SPI_TX_EN,
+	do {
+		writel(SIRFSOC_SPI_FIFO_RESET,
+			sspi->base + SIRFSOC_SPI_RXFIFO_OP);
+		writel(SIRFSOC_SPI_FIFO_RESET,
+			sspi->base + SIRFSOC_SPI_TXFIFO_OP);
+		writel(SIRFSOC_SPI_FIFO_START,
+			sspi->base + SIRFSOC_SPI_RXFIFO_OP);
+		writel(SIRFSOC_SPI_FIFO_START,
+			sspi->base + SIRFSOC_SPI_TXFIFO_OP);
+		writel(0, sspi->base + SIRFSOC_SPI_INT_EN);
+		writel(SIRFSOC_SPI_INT_MASK_ALL,
+			sspi->base + SIRFSOC_SPI_INT_STATUS);
+		writel(readl(sspi->base + SIRFSOC_SPI_CTRL) |
+			SIRFSOC_SPI_MUL_DAT_MODE | SIRFSOC_SPI_ENA_AUTO_CLR,
+			sspi->base + SIRFSOC_SPI_CTRL);
+		writel(min(sspi->left_tx_word, (u32)(256 / sspi->word_width))
+				- 1, sspi->base + SIRFSOC_SPI_TX_DMA_IO_LEN);
+		writel(min(sspi->left_rx_word, (u32)(256 / sspi->word_width))
+				- 1, sspi->base + SIRFSOC_SPI_RX_DMA_IO_LEN);
+		while (!((readl(sspi->base + SIRFSOC_SPI_TXFIFO_STATUS)
+			& SIRFSOC_SPI_FIFO_FULL)) && sspi->left_tx_word)
+			sspi->tx_word(sspi);
+		writel(SIRFSOC_SPI_TXFIFO_EMPTY_INT_EN |
+			SIRFSOC_SPI_TX_UFLOW_INT_EN |
+			SIRFSOC_SPI_RX_OFLOW_INT_EN,
+			sspi->base + SIRFSOC_SPI_INT_EN);
+		writel(SIRFSOC_SPI_RX_EN | SIRFSOC_SPI_TX_EN,
 			sspi->base + SIRFSOC_SPI_TX_RX_EN);
-	if (wait_for_completion_timeout(&sspi->rx_done, timeout) == 0)
-		dev_err(&spi->dev, "transfer timeout\n");
-	writel(0, sspi->base + SIRFSOC_SPI_RXFIFO_OP);
-	writel(0, sspi->base + SIRFSOC_SPI_TXFIFO_OP);
-	writel(0, sspi->base + SIRFSOC_SPI_TX_RX_EN);
-	writel(0, sspi->base + SIRFSOC_SPI_INT_EN);
+		if (!wait_for_completion_timeout(&sspi->tx_done, timeout) ||
+			!wait_for_completion_timeout(&sspi->rx_done, timeout)) {
+			dev_err(&spi->dev, "transfer timeout\n");
+			break;
+		}
+		while (!((readl(sspi->base + SIRFSOC_SPI_RXFIFO_STATUS)
+			& SIRFSOC_SPI_FIFO_EMPTY)) && sspi->left_rx_word)
+			sspi->rx_word(sspi);
+		writel(0, sspi->base + SIRFSOC_SPI_RXFIFO_OP);
+		writel(0, sspi->base + SIRFSOC_SPI_TXFIFO_OP);
+	} while (sspi->left_tx_word != 0 || sspi->left_rx_word != 0);
 }
 
 static int spi_sirfsoc_transfer(struct spi_device *spi, struct spi_transfer *t)