git: 1e7b0dc00076 - stable/12 - aw_spi: improve I/O stability

The branch stable/12 has been updated by avg:

URL: https://cgit.FreeBSD.org/src/commit/?id=1e7b0dc0007601b14ed656150b322498cd8c0fde

commit 1e7b0dc0007601b14ed656150b322498cd8c0fde
Author:     Andriy Gapon <avg@FreeBSD.org>
AuthorDate: 2021-12-20 10:40:17 +0000
Commit:     Andriy Gapon <avg@FreeBSD.org>
CommitDate: 2022-01-03 08:50:57 +0000

    aw_spi: improve I/O stability
    
    This driver does not use DMA at the moment, so some care is needed to
    prevent TX FIFO underruns and RX FIFO overflows.
    Several improvements are done in oder to minimize chances of those.
    
    First, the interrupt handling is moved to a filter to minimize latency.
    Second, FIFO trigger thresholds are configured for both FIFOs.
    The TX FIFO threshold is set to 3/4-th of its size and the RX FIFO
    threshold is set to 1/4-th of its size.
    The interrupt conditions are changed from the empty FIFO and full FIFO
    for the TX and RX correspondingly to going below and above the thresholds.
    
    While here I renamed AW_SPI_IER_RF_ERQ to AW_SPI_IER_RF_RDY which is
    closer to what the documentation uses, RF_RDY_INT_EN in the interrupt
    control register and RX_RDY in the interrupt status register.
    
    (cherry picked from commit 08ff54dc5b5de85580044167e1714fb75df8e44f)
---
 sys/arm/allwinner/aw_spi.c | 36 +++++++++++++++++++++++-------------
 1 file changed, 23 insertions(+), 13 deletions(-)

diff --git a/sys/arm/allwinner/aw_spi.c b/sys/arm/allwinner/aw_spi.c
index 629b808c6e72..2966011f0551 100644
--- a/sys/arm/allwinner/aw_spi.c
+++ b/sys/arm/allwinner/aw_spi.c
@@ -82,7 +82,7 @@ __FBSDID("$FreeBSD$");
 #define	 AW_SPI_IER_TF_ERQ	(1 << 4)	/* TXFIFO Empty Request */
 #define	 AW_SPI_IER_RF_FULL	(1 << 2)	/* RXFIFO Full */
 #define	 AW_SPI_IER_RF_EMP	(1 << 1)	/* RXFIFO Empty */
-#define	 AW_SPI_IER_RF_ERQ	(1 << 0)	/* RXFIFO Empty Request */
+#define	 AW_SPI_IER_RF_RDY	(1 << 0)	/* RXFIFO Ready Request */
 
 #define	AW_SPI_ISR		0x14		/* Interrupt Status Register */
 
@@ -167,7 +167,7 @@ struct aw_spi_softc {
 static int aw_spi_probe(device_t dev);
 static int aw_spi_attach(device_t dev);
 static int aw_spi_detach(device_t dev);
-static void aw_spi_intr(void *arg);
+static int aw_spi_intr(void *arg);
 
 static int
 aw_spi_probe(device_t dev)
@@ -200,7 +200,7 @@ aw_spi_attach(device_t dev)
 	}
 
 	if (bus_setup_intr(dev, sc->res[1],
-	    INTR_TYPE_MISC | INTR_MPSAFE, NULL, aw_spi_intr, sc,
+	    INTR_TYPE_MISC | INTR_MPSAFE, aw_spi_intr, NULL, sc,
 	    &sc->intrhand)) {
 		bus_release_resources(dev, aw_spi_spec, sc->res);
 		device_printf(dev, "cannot setup interrupt handler\n");
@@ -422,7 +422,7 @@ aw_spi_read_rxfifo(struct aw_spi_softc *sc)
 	}
 }
 
-static void
+static int
 aw_spi_intr(void *arg)
 {
 	struct aw_spi_softc *sc;
@@ -432,18 +432,19 @@ aw_spi_intr(void *arg)
 
 	intr = AW_SPI_READ_4(sc, AW_SPI_ISR);
 
-	if (intr & AW_SPI_IER_RF_FULL)
+	if (intr & AW_SPI_IER_RF_RDY)
 		aw_spi_read_rxfifo(sc);
 
-	if (intr & AW_SPI_IER_TF_EMP) {
+	if (intr & AW_SPI_IER_TF_ERQ) {
 		aw_spi_fill_txfifo(sc);
-		/* 
-		 * If we don't have anything else to write 
+
+		/*
+		 * If we don't have anything else to write
 		 * disable TXFifo interrupts
 		 */
 		if (sc->txcnt == sc->txlen)
 			AW_SPI_WRITE_4(sc, AW_SPI_IER, AW_SPI_IER_TC |
-			    AW_SPI_IER_RF_FULL);
+			    AW_SPI_IER_RF_RDY);
 	}
 
 	if (intr & AW_SPI_IER_TC) {
@@ -458,6 +459,7 @@ aw_spi_intr(void *arg)
 
 	/* Clear Interrupts */
 	AW_SPI_WRITE_4(sc, AW_SPI_ISR, intr);
+	return (intr != 0 ? FILTER_HANDLED : FILTER_STRAY);
 }
 
 static int
@@ -486,6 +488,14 @@ aw_spi_xfer(struct aw_spi_softc *sc, void *rxbuf, void *txbuf, uint32_t txlen, u
 		return (EIO);
 	}
 
+	/*
+	 * Set the TX FIFO threshold to 3/4-th the size and
+	 * the RX FIFO one to 1/4-th.
+	 */
+	AW_SPI_WRITE_4(sc, AW_SPI_FCR,
+	    ((3 * AW_SPI_FIFO_SIZE / 4) << AW_SPI_FCR_TX_TRIG_SHIFT) |
+	    ((AW_SPI_FIFO_SIZE / 4) << AW_SPI_FCR_RX_TRIG_SHIFT));
+
 	/* Write the counters */
 	AW_SPI_WRITE_4(sc, AW_SPI_MBC, txlen);
 	AW_SPI_WRITE_4(sc, AW_SPI_MTC, txlen);
@@ -499,14 +509,14 @@ aw_spi_xfer(struct aw_spi_softc *sc, void *rxbuf, void *txbuf, uint32_t txlen, u
 	reg |= AW_SPI_TCR_XCH;
 	AW_SPI_WRITE_4(sc, AW_SPI_TCR, reg);
 
-	/* 
+	/*
 	 * Enable interrupts for :
 	 * Transmit complete
-	 * TX Fifo empty
-	 * RX Fifo full
+	 * TX Fifo is below its trigger threshold
+	 * RX Fifo is above its trigger threshold
 	 */
 	AW_SPI_WRITE_4(sc, AW_SPI_IER, AW_SPI_IER_TC |
-	    AW_SPI_IER_TF_EMP | AW_SPI_IER_RF_FULL);
+	    AW_SPI_IER_TF_ERQ | AW_SPI_IER_RF_RDY);
 
 	sc->transfer = 1;