1 files changed, 49 insertions, 20 deletions

diff --git a/drivers/spi/au1550_spi.c b/drivers/spi/au1550_spi.c
index 3860dd2fa5d9..9149689c79d9 100644
--- a/drivers/spi/au1550_spi.c
+++ b/drivers/spi/au1550_spi.c
@@ -484,9 +484,13 @@ static irqreturn_t au1550_spi_dma_irq_callback(struct au1550_spi *hw)
 		au1xxx_dbdma_reset(hw->dma_tx_ch);
 		au1550_spi_reset_fifos(hw);
 
-		dev_err(hw->dev,
-			"Unexpected SPI error: event=0x%x stat=0x%x!\n",
-			evnt, stat);
+		if (evnt == PSC_SPIEVNT_RO)
+			dev_err(hw->dev,
+				"dma transfer: receive FIFO overflow!\n");
+		else
+			dev_err(hw->dev,
+				"dma transfer: unexpected SPI error "
+				"(event=0x%x stat=0x%x)!\n", evnt, stat);
 
 		complete(&hw->master_done);
 		return IRQ_HANDLED;
@@ -596,17 +600,17 @@ static irqreturn_t au1550_spi_pio_irq_callback(struct au1550_spi *hw)
 
 	if ((evnt & (PSC_SPIEVNT_MM | PSC_SPIEVNT_RO
 				| PSC_SPIEVNT_RU | PSC_SPIEVNT_TO
-				| PSC_SPIEVNT_TU | PSC_SPIEVNT_SD))
+				| PSC_SPIEVNT_SD))
 			!= 0) {
-		dev_err(hw->dev,
-			"Unexpected SPI error: event=0x%x stat=0x%x!\n",
-			evnt, stat);
 		/*
 		 * due to an error we consider transfer as done,
 		 * so mask all events until before next transfer start
 		 */
 		au1550_spi_mask_ack_all(hw);
 		au1550_spi_reset_fifos(hw);
+		dev_err(hw->dev,
+			"pio transfer: unexpected SPI error "
+			"(event=0x%x stat=0x%x)!\n", evnt, stat);
 		complete(&hw->master_done);
 		return IRQ_HANDLED;
 	}
@@ -620,27 +624,50 @@ static irqreturn_t au1550_spi_pio_irq_callback(struct au1550_spi *hw)
 		stat = hw->regs->psc_spistat;
 		au_sync();
 
-		if ((stat & PSC_SPISTAT_RE) == 0 && hw->rx_count < hw->len) {
+		/*
+		 * Take care to not let the Rx FIFO overflow.
+		 *
+		 * We only write a byte if we have read one at least. Initially,
+		 * the write fifo is full, so we should read from the read fifo
+		 * first.
+		 * In case we miss a word from the read fifo, we should get a
+		 * RO event and should back out.
+		 */
+		if (!(stat & PSC_SPISTAT_RE) && hw->rx_count < hw->len) {
 			hw->rx_word(hw);
-			/* ack the receive request event */
-			hw->regs->psc_spievent = PSC_SPIEVNT_RR;
-			au_sync();
 			busy = 1;
-		}
 
-		if ((stat & PSC_SPISTAT_TF) == 0 && hw->tx_count < hw->len) {
-			hw->tx_word(hw);
-			/* ack the transmit request event */
-			hw->regs->psc_spievent = PSC_SPIEVNT_TR;
-			au_sync();
-			busy = 1;
+			if (!(stat & PSC_SPISTAT_TF) && hw->tx_count < hw->len)
+				hw->tx_word(hw);
 		}
 	} while (busy);
 
-	evnt = hw->regs->psc_spievent;
+	hw->regs->psc_spievent = PSC_SPIEVNT_RR | PSC_SPIEVNT_TR;
 	au_sync();
 
-	if (hw->rx_count >= hw->len || (evnt & PSC_SPIEVNT_MD) != 0) {
+	/*
+	 * Restart the SPI transmission in case of a transmit underflow.
+	 * This seems to work despite the notes in the Au1550 data book
+	 * of Figure 8-4 with flowchart for SPI master operation:
+	 *
+	 * """Note 1: An XFR Error Interrupt occurs, unless masked,
+	 * for any of the following events: Tx FIFO Underflow,
+	 * Rx FIFO Overflow, or Multiple-master Error
+	 *    Note 2: In case of a Tx Underflow Error, all zeroes are
+	 * transmitted."""
+	 *
+	 * By simply restarting the spi transfer on Tx Underflow Error,
+	 * we assume that spi transfer was paused instead of zeroes
+	 * transmittion mentioned in the Note 2 of Au1550 data book.
+	 */
+	if (evnt & PSC_SPIEVNT_TU) {
+		hw->regs->psc_spievent = PSC_SPIEVNT_TU | PSC_SPIEVNT_MD;
+		au_sync();
+		hw->regs->psc_spipcr = PSC_SPIPCR_MS;
+		au_sync();
+	}
+
+	if (hw->rx_count >= hw->len) {
 		/* transfer completed successfully */
 		au1550_spi_mask_ack_all(hw);
 		complete(&hw->master_done);
@@ -729,6 +756,8 @@ static void __init au1550_spi_setup_psc_as_spi(struct au1550_spi *hw)
 		stat = hw->regs->psc_spistat;
 		au_sync();
 	} while ((stat & PSC_SPISTAT_DR) == 0);
+
+	au1550_spi_reset_fifos(hw);
 }