[PATCH] spi: spi-geni-qcom: Don't wait to start 1st transfer if transmitting

[Douglas Anderson <dianders@xxxxxxxxxxxx>]

If we're sending bytes over SPI, we know the FIFO is empty at the
start of the transfer.  There's no reason to wait for the interrupt
telling us to start--we can just start right away.  Then if we
transmit everything in one swell foop we don't even need to bother
listening for TX interrupts.

In a test of "flashrom -p ec -r /tmp/foo.bin" interrupts were reduced
from ~30560 to ~29730, about a 3% savings.

This patch looks bigger than it is because I moved a few functions
rather than adding a forward declaration.  The only actual change to
geni_spi_handle_tx() was to make it return a bool indicating if there
is more to tx.

Signed-off-by: Douglas Anderson <dianders@xxxxxxxxxxxx>
---

 drivers/spi/spi-geni-qcom.c | 167 +++++++++++++++++++-----------------
 1 file changed, 86 insertions(+), 81 deletions(-)

diff --git a/drivers/spi/spi-geni-qcom.c b/drivers/spi/spi-geni-qcom.c
index 0dc3f4c55b0b..49c9eb870755 100644
--- a/drivers/spi/spi-geni-qcom.c
+++ b/drivers/spi/spi-geni-qcom.c
@@ -326,6 +326,88 @@ static int spi_geni_init(struct spi_geni_master *mas)
 	return 0;
 }
 
+static unsigned int geni_byte_per_fifo_word(struct spi_geni_master *mas)
+{
+	/*
+	 * Calculate how many bytes we'll put in each FIFO word.  If the
+	 * transfer words don't pack cleanly into a FIFO word we'll just put
+	 * one transfer word in each FIFO word.  If they do pack we'll pack 'em.
+	 */
+	if (mas->fifo_width_bits % mas->cur_bits_per_word)
+		return roundup_pow_of_two(DIV_ROUND_UP(mas->cur_bits_per_word,
+						       BITS_PER_BYTE));
+
+	return mas->fifo_width_bits / BITS_PER_BYTE;
+}
+
+static bool geni_spi_handle_tx(struct spi_geni_master *mas)
+{
+	struct geni_se *se = &mas->se;
+	unsigned int max_bytes;
+	const u8 *tx_buf;
+	unsigned int bytes_per_fifo_word = geni_byte_per_fifo_word(mas);
+	unsigned int i = 0;
+
+	max_bytes = (mas->tx_fifo_depth - mas->tx_wm) * bytes_per_fifo_word;
+	if (mas->tx_rem_bytes < max_bytes)
+		max_bytes = mas->tx_rem_bytes;
+
+	tx_buf = mas->cur_xfer->tx_buf + mas->cur_xfer->len - mas->tx_rem_bytes;
+	while (i < max_bytes) {
+		unsigned int j;
+		unsigned int bytes_to_write;
+		u32 fifo_word = 0;
+		u8 *fifo_byte = (u8 *)&fifo_word;
+
+		bytes_to_write = min(bytes_per_fifo_word, max_bytes - i);
+		for (j = 0; j < bytes_to_write; j++)
+			fifo_byte[j] = tx_buf[i++];
+		iowrite32_rep(se->base + SE_GENI_TX_FIFOn, &fifo_word, 1);
+	}
+	mas->tx_rem_bytes -= max_bytes;
+	if (!mas->tx_rem_bytes) {
+		writel(0, se->base + SE_GENI_TX_WATERMARK_REG);
+		return false;
+	}
+	return true;
+}
+
+static void geni_spi_handle_rx(struct spi_geni_master *mas)
+{
+	struct geni_se *se = &mas->se;
+	u32 rx_fifo_status;
+	unsigned int rx_bytes;
+	unsigned int rx_last_byte_valid;
+	u8 *rx_buf;
+	unsigned int bytes_per_fifo_word = geni_byte_per_fifo_word(mas);
+	unsigned int i = 0;
+
+	rx_fifo_status = readl(se->base + SE_GENI_RX_FIFO_STATUS);
+	rx_bytes = (rx_fifo_status & RX_FIFO_WC_MSK) * bytes_per_fifo_word;
+	if (rx_fifo_status & RX_LAST) {
+		rx_last_byte_valid = rx_fifo_status & RX_LAST_BYTE_VALID_MSK;
+		rx_last_byte_valid >>= RX_LAST_BYTE_VALID_SHFT;
+		if (rx_last_byte_valid && rx_last_byte_valid < 4)
+			rx_bytes -= bytes_per_fifo_word - rx_last_byte_valid;
+	}
+	if (mas->rx_rem_bytes < rx_bytes)
+		rx_bytes = mas->rx_rem_bytes;
+
+	rx_buf = mas->cur_xfer->rx_buf + mas->cur_xfer->len - mas->rx_rem_bytes;
+	while (i < rx_bytes) {
+		u32 fifo_word = 0;
+		u8 *fifo_byte = (u8 *)&fifo_word;
+		unsigned int bytes_to_read;
+		unsigned int j;
+
+		bytes_to_read = min(bytes_per_fifo_word, rx_bytes - i);
+		ioread32_rep(se->base + SE_GENI_RX_FIFOn, &fifo_word, 1);
+		for (j = 0; j < bytes_to_read; j++)
+			rx_buf[i++] = fifo_byte[j];
+	}
+	mas->rx_rem_bytes -= rx_bytes;
+}
+
 static void setup_fifo_xfer(struct spi_transfer *xfer,
 				struct spi_geni_master *mas,
 				u16 mode, struct spi_master *spi)
@@ -398,8 +480,10 @@ static void setup_fifo_xfer(struct spi_transfer *xfer,
 	 * setting up GENI SE engine, as driver starts data transfer
 	 * for the watermark interrupt.
 	 */
-	if (m_cmd & SPI_TX_ONLY)
-		writel(mas->tx_wm, se->base + SE_GENI_TX_WATERMARK_REG);
+	if (m_cmd & SPI_TX_ONLY) {
+		if (geni_spi_handle_tx(mas))
+			writel(mas->tx_wm, se->base + SE_GENI_TX_WATERMARK_REG);
+	}
 	spin_unlock_irq(&mas->lock);
 }
 
@@ -417,85 +501,6 @@ static int spi_geni_transfer_one(struct spi_master *spi,
 	return 1;
 }
 
-static unsigned int geni_byte_per_fifo_word(struct spi_geni_master *mas)
-{
-	/*
-	 * Calculate how many bytes we'll put in each FIFO word.  If the
-	 * transfer words don't pack cleanly into a FIFO word we'll just put
-	 * one transfer word in each FIFO word.  If they do pack we'll pack 'em.
-	 */
-	if (mas->fifo_width_bits % mas->cur_bits_per_word)
-		return roundup_pow_of_two(DIV_ROUND_UP(mas->cur_bits_per_word,
-						       BITS_PER_BYTE));
-
-	return mas->fifo_width_bits / BITS_PER_BYTE;
-}
-
-static void geni_spi_handle_tx(struct spi_geni_master *mas)
-{
-	struct geni_se *se = &mas->se;
-	unsigned int max_bytes;
-	const u8 *tx_buf;
-	unsigned int bytes_per_fifo_word = geni_byte_per_fifo_word(mas);
-	unsigned int i = 0;
-
-	max_bytes = (mas->tx_fifo_depth - mas->tx_wm) * bytes_per_fifo_word;
-	if (mas->tx_rem_bytes < max_bytes)
-		max_bytes = mas->tx_rem_bytes;
-
-	tx_buf = mas->cur_xfer->tx_buf + mas->cur_xfer->len - mas->tx_rem_bytes;
-	while (i < max_bytes) {
-		unsigned int j;
-		unsigned int bytes_to_write;
-		u32 fifo_word = 0;
-		u8 *fifo_byte = (u8 *)&fifo_word;
-
-		bytes_to_write = min(bytes_per_fifo_word, max_bytes - i);
-		for (j = 0; j < bytes_to_write; j++)
-			fifo_byte[j] = tx_buf[i++];
-		iowrite32_rep(se->base + SE_GENI_TX_FIFOn, &fifo_word, 1);
-	}
-	mas->tx_rem_bytes -= max_bytes;
-	if (!mas->tx_rem_bytes)
-		writel(0, se->base + SE_GENI_TX_WATERMARK_REG);
-}
-
-static void geni_spi_handle_rx(struct spi_geni_master *mas)
-{
-	struct geni_se *se = &mas->se;
-	u32 rx_fifo_status;
-	unsigned int rx_bytes;
-	unsigned int rx_last_byte_valid;
-	u8 *rx_buf;
-	unsigned int bytes_per_fifo_word = geni_byte_per_fifo_word(mas);
-	unsigned int i = 0;
-
-	rx_fifo_status = readl(se->base + SE_GENI_RX_FIFO_STATUS);
-	rx_bytes = (rx_fifo_status & RX_FIFO_WC_MSK) * bytes_per_fifo_word;
-	if (rx_fifo_status & RX_LAST) {
-		rx_last_byte_valid = rx_fifo_status & RX_LAST_BYTE_VALID_MSK;
-		rx_last_byte_valid >>= RX_LAST_BYTE_VALID_SHFT;
-		if (rx_last_byte_valid && rx_last_byte_valid < 4)
-			rx_bytes -= bytes_per_fifo_word - rx_last_byte_valid;
-	}
-	if (mas->rx_rem_bytes < rx_bytes)
-		rx_bytes = mas->rx_rem_bytes;
-
-	rx_buf = mas->cur_xfer->rx_buf + mas->cur_xfer->len - mas->rx_rem_bytes;
-	while (i < rx_bytes) {
-		u32 fifo_word = 0;
-		u8 *fifo_byte = (u8 *)&fifo_word;
-		unsigned int bytes_to_read;
-		unsigned int j;
-
-		bytes_to_read = min(bytes_per_fifo_word, rx_bytes - i);
-		ioread32_rep(se->base + SE_GENI_RX_FIFOn, &fifo_word, 1);
-		for (j = 0; j < bytes_to_read; j++)
-			rx_buf[i++] = fifo_byte[j];
-	}
-	mas->rx_rem_bytes -= rx_bytes;
-}
-
 static irqreturn_t geni_spi_isr(int irq, void *data)
 {
 	struct spi_master *spi = data;
-- 
2.28.0.618.gf4bc123cb7-goog