[PATCH v2 1/3] dmaengine: hsu: Export hsu_dma_get_status()

[Chuah Kim Tatt]

From: "Chuah, Kim Tatt" <kim.tatt.chuah@xxxxxxxxx>

To allow other code to safely read DMA Channel Status Register (where
the register attribute for Channel Error, Descriptor Time Out &
Descriptor Done fields are read-clear), export hsu_dma_get_status().
hsu_dma_irq() is renamed to hsu_dma_do_irq() and requires Status
Register value to be passed in.

Signed-off-by: Chuah, Kim Tatt <kim.tatt.chuah@xxxxxxxxx>
---
 drivers/dma/hsu/hsu.c              | 90 +++++++++++++++++++++++++++++---------
 drivers/dma/hsu/pci.c              | 11 ++++-
 drivers/tty/serial/8250/8250_mid.c | 22 +++++++---
 include/linux/dma/hsu.h            | 14 ++++--
 4 files changed, 106 insertions(+), 31 deletions(-)

diff --git a/drivers/dma/hsu/hsu.c b/drivers/dma/hsu/hsu.c
index f8c5cd5..c5f21ef 100644
--- a/drivers/dma/hsu/hsu.c
+++ b/drivers/dma/hsu/hsu.c
@@ -126,28 +126,33 @@ static void hsu_dma_start_transfer(struct hsu_dma_chan *hsuc)
 	hsu_dma_start_channel(hsuc);
 }
 
-static u32 hsu_dma_chan_get_sr(struct hsu_dma_chan *hsuc)
-{
-	unsigned long flags;
-	u32 sr;
-
-	spin_lock_irqsave(&hsuc->vchan.lock, flags);
-	sr = hsu_chan_readl(hsuc, HSU_CH_SR);
-	spin_unlock_irqrestore(&hsuc->vchan.lock, flags);
-
-	return sr & ~(HSU_CH_SR_DESCE_ANY | HSU_CH_SR_CDESC_ANY);
-}
-
-irqreturn_t hsu_dma_irq(struct hsu_dma_chip *chip, unsigned short nr)
+/*
+ *      hsu_dma_get_status() - get DMA channel status
+ *      @chip: HSUART DMA chip
+ *      @nr: DMA channel number
+ *      @status: pointer for DMA Channel Status Register value
+ *
+ *      Description:
+ *      The function reads and clears the DMA Channel Status Register, checks
+ *      if it was a timeout interrupt and returns a corresponding value.
+ *
+ *      Caller should provide a valid pointer for the DMA Channel Status
+ *      Register value that will be returned in @status.
+ *
+ *      Return:
+ *      1 for DMA timeout status, 0 for other DMA status, or error code for
+ *      invalid parameters or no interrupt pending.
+ */
+int hsu_dma_get_status(struct hsu_dma_chip *chip, unsigned short nr,
+		       u32 *status)
 {
 	struct hsu_dma_chan *hsuc;
-	struct hsu_dma_desc *desc;
 	unsigned long flags;
 	u32 sr;
 
 	/* Sanity check */
 	if (nr >= chip->hsu->nr_channels)
-		return IRQ_NONE;
+		return -EINVAL;
 
 	hsuc = &chip->hsu->chan[nr];
 
@@ -155,22 +160,65 @@ irqreturn_t hsu_dma_irq(struct hsu_dma_chip *chip, unsigned short nr)
 	 * No matter what situation, need read clear the IRQ status
 	 * There is a bug, see Errata 5, HSD 2900918
 	 */
-	sr = hsu_dma_chan_get_sr(hsuc);
+	spin_lock_irqsave(&hsuc->vchan.lock, flags);
+	sr = hsu_chan_readl(hsuc, HSU_CH_SR);
+	spin_unlock_irqrestore(&hsuc->vchan.lock, flags);
+
+	/* Check if any interrupt is pending */
+	sr &= ~(HSU_CH_SR_DESCE_ANY | HSU_CH_SR_CDESC_ANY);
 	if (!sr)
-		return IRQ_NONE;
+		return -EIO;
 
 	/* Timeout IRQ, need wait some time, see Errata 2 */
 	if (sr & HSU_CH_SR_DESCTO_ANY)
 		udelay(2);
 
+	/*
+	 * At this point, at least one of Descriptor Time Out, Channel Error
+	 * or Descriptor Done bits must be set. Clear the Descriptor Time Out
+	 * bits and if sr is still non-zero, it must be channel error or
+	 * descriptor done which are higher priority than timeout and handled
+	 * in hsu_dma_do_irq(). Else, it must be a timeout.
+	 */
 	sr &= ~HSU_CH_SR_DESCTO_ANY;
-	if (!sr)
-		return IRQ_HANDLED;
+
+	*status = sr;
+
+	return sr ? 0 : 1;
+}
+EXPORT_SYMBOL_GPL(hsu_dma_get_status);
+
+/*
+ *      hsu_dma_do_irq() - DMA interrupt handler
+ *      @chip: HSUART DMA chip
+ *      @nr: DMA channel number
+ *      @status: Channel Status Register value
+ *
+ *      Description:
+ *      This function handles Channel Error and Descriptor Done interrupts.
+ *      This function should be called after determining that the DMA interrupt
+ *      is not a normal timeout interrupt, ie. hsu_dma_get_status() returned 0.
+ *
+ *      Return:
+ *      IRQ_NONE for invalid channel number, IRQ_HANDLED otherwise.
+ */
+irqreturn_t hsu_dma_do_irq(struct hsu_dma_chip *chip, unsigned short nr,
+			   u32 status)
+{
+	struct hsu_dma_chan *hsuc;
+	struct hsu_dma_desc *desc;
+	unsigned long flags;
+
+	/* Sanity check */
+	if (nr >= chip->hsu->nr_channels)
+		return IRQ_NONE;
+
+	hsuc = &chip->hsu->chan[nr];
 
 	spin_lock_irqsave(&hsuc->vchan.lock, flags);
 	desc = hsuc->desc;
 	if (desc) {
-		if (sr & HSU_CH_SR_CHE) {
+		if (status & HSU_CH_SR_CHE) {
 			desc->status = DMA_ERROR;
 		} else if (desc->active < desc->nents) {
 			hsu_dma_start_channel(hsuc);
@@ -184,7 +232,7 @@ irqreturn_t hsu_dma_irq(struct hsu_dma_chip *chip, unsigned short nr)
 
 	return IRQ_HANDLED;
 }
-EXPORT_SYMBOL_GPL(hsu_dma_irq);
+EXPORT_SYMBOL_GPL(hsu_dma_do_irq);
 
 static struct hsu_dma_desc *hsu_dma_alloc_desc(unsigned int nents)
 {
diff --git a/drivers/dma/hsu/pci.c b/drivers/dma/hsu/pci.c
index e2db76b..9916058 100644
--- a/drivers/dma/hsu/pci.c
+++ b/drivers/dma/hsu/pci.c
@@ -27,13 +27,20 @@ static irqreturn_t hsu_pci_irq(int irq, void *dev)
 {
 	struct hsu_dma_chip *chip = dev;
 	u32 dmaisr;
+	u32 status;
 	unsigned short i;
 	irqreturn_t ret = IRQ_NONE;
+	int err;
 
 	dmaisr = readl(chip->regs + HSU_PCI_DMAISR);
 	for (i = 0; i < chip->hsu->nr_channels; i++) {
-		if (dmaisr & 0x1)
-			ret |= hsu_dma_irq(chip, i);
+		if (dmaisr & 0x1) {
+			err = hsu_dma_get_status(chip, i, &status);
+			if (err > 0)
+				ret |= IRQ_HANDLED;
+			else if (err == 0)
+				ret |= hsu_dma_do_irq(chip, i, status);
+		}
 		dmaisr >>= 1;
 	}
 
diff --git a/drivers/tty/serial/8250/8250_mid.c b/drivers/tty/serial/8250/8250_mid.c
index 86379a7..b218ff5 100644
--- a/drivers/tty/serial/8250/8250_mid.c
+++ b/drivers/tty/serial/8250/8250_mid.c
@@ -97,12 +97,24 @@ static int dnv_handle_irq(struct uart_port *p)
 {
 	struct mid8250 *mid = p->private_data;
 	unsigned int fisr = serial_port_in(p, INTEL_MID_UART_DNV_FISR);
+	u32 status;
 	int ret = IRQ_NONE;
-
-	if (fisr & BIT(2))
-		ret |= hsu_dma_irq(&mid->dma_chip, 1);
-	if (fisr & BIT(1))
-		ret |= hsu_dma_irq(&mid->dma_chip, 0);
+	int err;
+
+	if (fisr & BIT(2)) {
+		err = hsu_dma_get_status(&mid->dma_chip, 1, &status);
+		if (err > 0)
+			ret |= IRQ_HANDLED;
+		else if (err == 0)
+			ret |= hsu_dma_do_irq(&mid->dma_chip, 1, status);
+	}
+	if (fisr & BIT(1)) {
+		err = hsu_dma_get_status(&mid->dma_chip, 0, &status);
+		if (err > 0)
+			ret |= IRQ_HANDLED;
+		else if (err == 0)
+			ret |= hsu_dma_do_irq(&mid->dma_chip, 0, status);
+	}
 	if (fisr & BIT(0))
 		ret |= serial8250_handle_irq(p, serial_port_in(p, UART_IIR));
 	return ret;
diff --git a/include/linux/dma/hsu.h b/include/linux/dma/hsu.h
index 79df69d..aaff68e 100644
--- a/include/linux/dma/hsu.h
+++ b/include/linux/dma/hsu.h
@@ -39,14 +39,22 @@ struct hsu_dma_chip {
 
 #if IS_ENABLED(CONFIG_HSU_DMA)
 /* Export to the internal users */
-irqreturn_t hsu_dma_irq(struct hsu_dma_chip *chip, unsigned short nr);
+int hsu_dma_get_status(struct hsu_dma_chip *chip, unsigned short nr,
+		       u32 *status);
+irqreturn_t hsu_dma_do_irq(struct hsu_dma_chip *chip, unsigned short nr,
+			   u32 status);
 
 /* Export to the platform drivers */
 int hsu_dma_probe(struct hsu_dma_chip *chip);
 int hsu_dma_remove(struct hsu_dma_chip *chip);
 #else
-static inline irqreturn_t hsu_dma_irq(struct hsu_dma_chip *chip,
-				      unsigned short nr)
+static inline int hsu_dma_get_status(struct hsu_dma_chip *chip,
+				     unsigned short nr, u32 *status)
+{
+	return 0;
+}
+static inline irqreturn_t hsu_dma_do_irq(struct hsu_dma_chip *chip,
+					 unsigned short nr, u32 status)
 {
 	return IRQ_NONE;
 }
-- 
1.9.1