Applied "spi: fsl-espi: fix and improve writing to TX FIFO" to the spi tree

[Mark Brown <broonie@xxxxxxxxxx>]

The patch

   spi: fsl-espi: fix and improve writing to TX FIFO

has been applied to the spi tree at

   git://git.kernel.org/pub/scm/linux/kernel/git/broonie/spi.git 

All being well this means that it will be integrated into the linux-next
tree (usually sometime in the next 24 hours) and sent to Linus during
the next merge window (or sooner if it is a bug fix), however if
problems are discovered then the patch may be dropped or reverted.  

You may get further e-mails resulting from automated or manual testing
and review of the tree, please engage with people reporting problems and
send followup patches addressing any issues that are reported if needed.

If any updates are required or you are submitting further changes they
should be sent as incremental updates against current git, existing
patches will not be replaced.

Please add any relevant lists and maintainers to the CCs when replying
to this mail.

Thanks,
Mark

>From 54731265966db742dda09008bd9bbe12ae11e93e Mon Sep 17 00:00:00 2001
From: Heiner Kallweit <hkallweit1@xxxxxxxxx>
Date: Thu, 27 Oct 2016 21:25:58 +0200
Subject: [PATCH] spi: fsl-espi: fix and improve writing to TX FIFO

This change addresses two issues:
- If the TX FIFO is full the ISR polls until there's free space again.
  An ISR should never wait for something.
- Currently the number of bytes to transfer is rounded up to the next
  multiple of 4. For most transfers therefore few bytes remain in the
  TX FIFO after end of transfer.
  This would cause the next transfer to fail and as a workaround the
  ESPI block is disabled / re-enabled in fsl_espi_change_mode.
  This seems to clear the FIFO's (although it's not mentioned in the
  spec).

With this change the TX FIFO is filled as much as possible initially
and whenever the ISR is called. Also the exact number of bytes is
transferred.
The spinlock protects against a potential race if the first interrupt
occurs whilst the TX FIFO is still being initially filled.

Signed-off-by: Heiner Kallweit <hkallweit1@xxxxxxxxx>
Signed-off-by: Mark Brown <broonie@xxxxxxxxxx>
---
 drivers/spi/spi-fsl-espi.c | 68 ++++++++++++++++++++++++++++------------------
 drivers/spi/spi-fsl-lib.h  |  2 ++
 2 files changed, 44 insertions(+), 26 deletions(-)

diff --git a/drivers/spi/spi-fsl-espi.c b/drivers/spi/spi-fsl-espi.c
index f04c2464e854..95c1fbfe1cbe 100644
--- a/drivers/spi/spi-fsl-espi.c
+++ b/drivers/spi/spi-fsl-espi.c
@@ -54,6 +54,8 @@
 #define CSMODE_AFT(x)		((x) << 8)
 #define CSMODE_CG(x)		((x) << 3)
 
+#define FSL_ESPI_FIFO_SIZE	32
+
 /* Default mode/csmode for eSPI controller */
 #define SPMODE_INIT_VAL (SPMODE_TXTHR(4) | SPMODE_RXTHR(3))
 #define CSMODE_INIT_VAL (CSMODE_POL_1 | CSMODE_BEF(0) \
@@ -200,6 +202,27 @@ static int fsl_espi_check_message(struct spi_message *m)
 	return 0;
 }
 
+static void fsl_espi_fill_tx_fifo(struct mpc8xxx_spi *mspi, u32 events)
+{
+	u32 tx_fifo_avail;
+
+	/* if events is zero transfer has not started and tx fifo is empty */
+	tx_fifo_avail = events ? SPIE_TXCNT(events) :  FSL_ESPI_FIFO_SIZE;
+
+	while (tx_fifo_avail >= min(4U, mspi->tx_len) && mspi->tx_len)
+		if (mspi->tx_len >= 4) {
+			fsl_espi_write_reg(mspi, ESPI_SPITF, *(u32 *)mspi->tx);
+			mspi->tx += 4;
+			mspi->tx_len -= 4;
+			tx_fifo_avail -= 4;
+		} else {
+			fsl_espi_write_reg8(mspi, ESPI_SPITF, *(u8 *)mspi->tx);
+			mspi->tx += 1;
+			mspi->tx_len -= 1;
+			tx_fifo_avail -= 1;
+		}
+}
+
 static void fsl_espi_change_mode(struct spi_device *spi)
 {
 	struct mpc8xxx_spi *mspi = spi_master_get_devdata(spi->master);
@@ -262,7 +285,7 @@ static int fsl_espi_bufs(struct spi_device *spi, struct spi_transfer *t)
 	int ret;
 
 	mpc8xxx_spi->len = t->len;
-	mpc8xxx_spi->count = roundup(t->len, 4) / 4;
+	mpc8xxx_spi->tx_len = t->len;
 
 	mpc8xxx_spi->tx = t->tx_buf;
 	mpc8xxx_spi->rx = t->rx_buf;
@@ -276,21 +299,22 @@ static int fsl_espi_bufs(struct spi_device *spi, struct spi_transfer *t)
 	/* enable rx ints */
 	fsl_espi_write_reg(mpc8xxx_spi, ESPI_SPIM, SPIM_RNE);
 
-	/* transmit word */
-	fsl_espi_write_reg(mpc8xxx_spi, ESPI_SPITF, *(u32 *)mpc8xxx_spi->tx);
-	mpc8xxx_spi->tx += 4;
+	/* Prevent filling the fifo from getting interrupted */
+	spin_lock_irq(&mpc8xxx_spi->lock);
+	fsl_espi_fill_tx_fifo(mpc8xxx_spi, 0);
+	spin_unlock_irq(&mpc8xxx_spi->lock);
 
 	/* Won't hang up forever, SPI bus sometimes got lost interrupts... */
 	ret = wait_for_completion_timeout(&mpc8xxx_spi->done, 2 * HZ);
 	if (ret == 0)
 		dev_err(mpc8xxx_spi->dev,
-			"Transaction hanging up (left %d bytes)\n",
-			mpc8xxx_spi->count);
+			"Transaction hanging up (left %u bytes)\n",
+			mpc8xxx_spi->tx_len);
 
 	/* disable rx ints */
 	fsl_espi_write_reg(mpc8xxx_spi, ESPI_SPIM, 0);
 
-	return mpc8xxx_spi->count > 0 ? -EMSGSIZE : 0;
+	return mpc8xxx_spi->tx_len > 0 ? -EMSGSIZE : 0;
 }
 
 static int fsl_espi_trans(struct spi_message *m, struct spi_transfer *trans)
@@ -461,26 +485,11 @@ static void fsl_espi_cpu_irq(struct mpc8xxx_spi *mspi, u32 events)
 		}
 	}
 
-	if (!(events & SPIE_TNF)) {
-		int ret;
-
-		/* spin until TX is done */
-		ret = spin_event_timeout(((events = fsl_espi_read_reg(
-				mspi, ESPI_SPIE)) & SPIE_TNF), 1000, 0);
-		if (!ret) {
-			dev_err(mspi->dev, "tired waiting for SPIE_TNF\n");
-			complete(&mspi->done);
-			return;
-		}
-	}
+	if (mspi->tx_len)
+		fsl_espi_fill_tx_fifo(mspi, events);
 
-	mspi->count -= 1;
-	if (mspi->count) {
-		fsl_espi_write_reg(mspi, ESPI_SPITF, *(u32 *)mspi->tx);
-		mspi->tx += 4;
-	} else {
+	if (!mspi->tx_len && !mspi->len)
 		complete(&mspi->done);
-	}
 }
 
 static irqreturn_t fsl_espi_irq(s32 irq, void *context_data)
@@ -488,10 +497,14 @@ static irqreturn_t fsl_espi_irq(s32 irq, void *context_data)
 	struct mpc8xxx_spi *mspi = context_data;
 	u32 events;
 
+	spin_lock(&mspi->lock);
+
 	/* Get interrupt events(tx/rx) */
 	events = fsl_espi_read_reg(mspi, ESPI_SPIE);
-	if (!events)
+	if (!events) {
+		spin_unlock_irq(&mspi->lock);
 		return IRQ_NONE;
+	}
 
 	dev_vdbg(mspi->dev, "%s: events %x\n", __func__, events);
 
@@ -500,6 +513,8 @@ static irqreturn_t fsl_espi_irq(s32 irq, void *context_data)
 	/* Clear the events */
 	fsl_espi_write_reg(mspi, ESPI_SPIE, events);
 
+	spin_unlock(&mspi->lock);
+
 	return IRQ_HANDLED;
 }
 
@@ -562,6 +577,7 @@ static int fsl_espi_probe(struct device *dev, struct resource *mem,
 	master->max_message_size = fsl_espi_max_message_size;
 
 	mpc8xxx_spi = spi_master_get_devdata(master);
+	spin_lock_init(&mpc8xxx_spi->lock);
 
 	mpc8xxx_spi->local_buf =
 		devm_kmalloc(dev, SPCOM_TRANLEN_MAX, GFP_KERNEL);
diff --git a/drivers/spi/spi-fsl-lib.h b/drivers/spi/spi-fsl-lib.h
index 2925c8089fd9..24d8bc84a111 100644
--- a/drivers/spi/spi-fsl-lib.h
+++ b/drivers/spi/spi-fsl-lib.h
@@ -30,7 +30,9 @@ struct mpc8xxx_spi {
 	void *rx;
 #if IS_ENABLED(CONFIG_SPI_FSL_ESPI)
 	int len;
+	unsigned int tx_len;
 	u8 *local_buf;
+	spinlock_t lock;
 #endif
 
 	int subblock;
-- 
2.10.1

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