diff mbox series

[07/13] i2c: nomadik: support short xfer timeouts using waitqueue & hrtimer

Message ID 20240215-mbly-i2c-v1-7-19a336e91dca@bootlin.com
State Superseded
Headers show
Series Add Mobileye EyeQ5 support to the Nomadik I2C controller & use hrtimers for timeouts | expand

Commit Message

Théo Lebrun Feb. 15, 2024, 4:52 p.m. UTC 
Replace the completion by a waitqueue for synchronization from IRQ
handler to task. For short timeouts, use hrtimers, else use timers.
Usecase: avoid blocking the I2C bus for too long when an issue occurs.

The threshold picked is one jiffy: if timeout is below that, use
hrtimers. This threshold is NOT configurable.

Implement behavior but do NOT change fetching of timeout. This means the
timeout is unchanged (200ms) and the hrtimer case will never trigger.

A waitqueue is used because it supports both desired timeout approaches.
See wait_event_timeout() and wait_event_hrtimeout(). An atomic boolean
serves as synchronization condition.

Signed-off-by: Théo Lebrun <theo.lebrun@bootlin.com>
---
 drivers/i2c/busses/i2c-nomadik.c | 70 +++++++++++++++++++++++++++-------------
 1 file changed, 48 insertions(+), 22 deletions(-)

Comments

Linus Walleij Feb. 19, 2024, 2:19 p.m. UTC | #1 
On Thu, Feb 15, 2024 at 5:52 PM Théo Lebrun <theo.lebrun@bootlin.com> wrote:

> Replace the completion by a waitqueue for synchronization from IRQ
> handler to task. For short timeouts, use hrtimers, else use timers.
> Usecase: avoid blocking the I2C bus for too long when an issue occurs.
>
> The threshold picked is one jiffy: if timeout is below that, use
> hrtimers. This threshold is NOT configurable.
>
> Implement behavior but do NOT change fetching of timeout. This means the
> timeout is unchanged (200ms) and the hrtimer case will never trigger.
>
> A waitqueue is used because it supports both desired timeout approaches.
> See wait_event_timeout() and wait_event_hrtimeout(). An atomic boolean
> serves as synchronization condition.
>
> Signed-off-by: Théo Lebrun <theo.lebrun@bootlin.com>

Part of me want to go and fix completions to handle hrtimer timeouts
for submicrosecond timeouts, BUT I realized that this is a bit thick
request for a simple driver, so just a suggestion for something we could
do one day. This is fine with me.
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>

Yours,
Linus Walleij
Théo Lebrun Feb. 19, 2024, 2:31 p.m. UTC | #2 
Hello,

On Mon Feb 19, 2024 at 3:19 PM CET, Linus Walleij wrote:
> On Thu, Feb 15, 2024 at 5:52 PM Théo Lebrun <theo.lebrun@bootlin.com> wrote:
>
> > Replace the completion by a waitqueue for synchronization from IRQ
> > handler to task. For short timeouts, use hrtimers, else use timers.
> > Usecase: avoid blocking the I2C bus for too long when an issue occurs.
> >
> > The threshold picked is one jiffy: if timeout is below that, use
> > hrtimers. This threshold is NOT configurable.
> >
> > Implement behavior but do NOT change fetching of timeout. This means the
> > timeout is unchanged (200ms) and the hrtimer case will never trigger.
> >
> > A waitqueue is used because it supports both desired timeout approaches.
> > See wait_event_timeout() and wait_event_hrtimeout(). An atomic boolean
> > serves as synchronization condition.
> >
> > Signed-off-by: Théo Lebrun <theo.lebrun@bootlin.com>
>
> Part of me want to go and fix completions to handle hrtimer timeouts
> for submicrosecond timeouts, BUT I realized that this is a bit thick
> request for a simple driver, so just a suggestion for something we could
> do one day. This is fine with me.
> Reviewed-by: Linus Walleij <linus.walleij@linaro.org>

Indeed having to switch to another abstraction because we desire another
timeout method is nonsensical. Completion supporting hrtimeouts would
make sense. As you said though, this is too much for a simple driver.

Thanks,

--
Théo Lebrun, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com

------------------------------------------------------------------------
diff mbox series

Patch

diff --git a/drivers/i2c/busses/i2c-nomadik.c b/drivers/i2c/busses/i2c-nomadik.c
index aa68ab402b10..e68b8e0d7919 100644
--- a/drivers/i2c/busses/i2c-nomadik.c
+++ b/drivers/i2c/busses/i2c-nomadik.c
@@ -162,10 +162,11 @@  struct i2c_nmk_client {
  * @clk_freq: clock frequency for the operation mode
  * @tft: Tx FIFO Threshold in bytes
  * @rft: Rx FIFO Threshold in bytes
- * @timeout: Slave response timeout (ms)
+ * @timeout_usecs: Slave response timeout
  * @sm: speed mode
  * @stop: stop condition.
- * @xfer_complete: acknowledge completion for a I2C message.
+ * @xfer_wq: xfer done wait queue.
+ * @xfer_done: xfer done boolean.
  * @result: controller propogated result.
  */
 struct nmk_i2c_dev {
@@ -179,10 +180,11 @@  struct nmk_i2c_dev {
 	u32				clk_freq;
 	unsigned char			tft;
 	unsigned char			rft;
-	int				timeout;
+	int				timeout_usecs;
 	enum i2c_freq_mode		sm;
 	int				stop;
-	struct completion		xfer_complete;
+	struct wait_queue_head		xfer_wq;
+	bool				xfer_done;
 	int				result;
 };
 
@@ -434,6 +436,22 @@  static void setup_i2c_controller(struct nmk_i2c_dev *priv)
 	writel(priv->rft, priv->virtbase + I2C_RFTR);
 }
 
+static bool nmk_i2c_wait_xfer_done(struct nmk_i2c_dev *priv)
+{
+	if (priv->timeout_usecs < jiffies_to_usecs(1)) {
+		unsigned long timeout_usecs = priv->timeout_usecs;
+		ktime_t timeout = ktime_set(0, timeout_usecs * NSEC_PER_USEC);
+
+		wait_event_hrtimeout(priv->xfer_wq, priv->xfer_done, timeout);
+	} else {
+		unsigned long timeout = usecs_to_jiffies(priv->timeout_usecs);
+
+		wait_event_timeout(priv->xfer_wq, priv->xfer_done, timeout);
+	}
+
+	return priv->xfer_done;
+}
+
 /**
  * read_i2c() - Read from I2C client device
  * @priv: private data of I2C Driver
@@ -445,9 +463,9 @@  static void setup_i2c_controller(struct nmk_i2c_dev *priv)
  */
 static int read_i2c(struct nmk_i2c_dev *priv, u16 flags)
 {
-	int status = 0;
 	u32 mcr, irq_mask;
-	unsigned long timeout;
+	int status = 0;
+	bool xfer_done;
 
 	mcr = load_i2c_mcr_reg(priv, flags);
 	writel(mcr, priv->virtbase + I2C_MCR);
@@ -459,7 +477,8 @@  static int read_i2c(struct nmk_i2c_dev *priv, u16 flags)
 	/* enable the controller */
 	i2c_set_bit(priv->virtbase + I2C_CR, I2C_CR_PE);
 
-	init_completion(&priv->xfer_complete);
+	init_waitqueue_head(&priv->xfer_wq);
+	priv->xfer_done = false;
 
 	/* enable interrupts by setting the mask */
 	irq_mask = (I2C_IT_RXFNF | I2C_IT_RXFF |
@@ -475,10 +494,9 @@  static int read_i2c(struct nmk_i2c_dev *priv, u16 flags)
 	writel(readl(priv->virtbase + I2C_IMSCR) | irq_mask,
 	       priv->virtbase + I2C_IMSCR);
 
-	timeout = wait_for_completion_timeout(
-		&priv->xfer_complete, priv->adap.timeout);
+	xfer_done = nmk_i2c_wait_xfer_done(priv);
 
-	if (timeout == 0) {
+	if (!xfer_done) {
 		/* Controller timed out */
 		dev_err(&priv->adev->dev, "read from slave 0x%x timed out\n",
 			priv->cli.slave_adr);
@@ -513,9 +531,9 @@  static void fill_tx_fifo(struct nmk_i2c_dev *priv, int no_bytes)
  */
 static int write_i2c(struct nmk_i2c_dev *priv, u16 flags)
 {
-	u32 status = 0;
 	u32 mcr, irq_mask;
-	unsigned long timeout;
+	u32 status = 0;
+	bool xfer_done;
 
 	mcr = load_i2c_mcr_reg(priv, flags);
 
@@ -528,7 +546,8 @@  static int write_i2c(struct nmk_i2c_dev *priv, u16 flags)
 	/* enable the controller */
 	i2c_set_bit(priv->virtbase + I2C_CR, I2C_CR_PE);
 
-	init_completion(&priv->xfer_complete);
+	init_waitqueue_head(&priv->xfer_wq);
+	priv->xfer_done = false;
 
 	/* enable interrupts by settings the masks */
 	irq_mask = (I2C_IT_TXFOVR | I2C_IT_MAL | I2C_IT_BERR);
@@ -554,10 +573,9 @@  static int write_i2c(struct nmk_i2c_dev *priv, u16 flags)
 	writel(readl(priv->virtbase + I2C_IMSCR) | irq_mask,
 	       priv->virtbase + I2C_IMSCR);
 
-	timeout = wait_for_completion_timeout(
-		&priv->xfer_complete, priv->adap.timeout);
+	xfer_done = nmk_i2c_wait_xfer_done(priv);
 
-	if (timeout == 0) {
+	if (!xfer_done) {
 		/* Controller timed out */
 		dev_err(&priv->adev->dev, "write to slave 0x%x timed out\n",
 			priv->cli.slave_adr);
@@ -807,7 +825,9 @@  static irqreturn_t i2c_irq_handler(int irq, void *arg)
 				priv->cli.count);
 			init_hw(priv);
 		}
-		complete(&priv->xfer_complete);
+		priv->xfer_done = true;
+		wake_up(&priv->xfer_wq);
+
 
 		break;
 
@@ -817,7 +837,9 @@  static irqreturn_t i2c_irq_handler(int irq, void *arg)
 		init_hw(priv);
 
 		i2c_set_bit(priv->virtbase + I2C_ICR, I2C_IT_MAL);
-		complete(&priv->xfer_complete);
+		priv->xfer_done = true;
+		wake_up(&priv->xfer_wq);
+
 
 		break;
 
@@ -834,7 +856,9 @@  static irqreturn_t i2c_irq_handler(int irq, void *arg)
 			init_hw(priv);
 
 		i2c_set_bit(priv->virtbase + I2C_ICR, I2C_IT_BERR);
-		complete(&priv->xfer_complete);
+		priv->xfer_done = true;
+		wake_up(&priv->xfer_wq);
+
 	}
 	break;
 
@@ -848,7 +872,9 @@  static irqreturn_t i2c_irq_handler(int irq, void *arg)
 		init_hw(priv);
 
 		dev_err(dev, "Tx Fifo Over run\n");
-		complete(&priv->xfer_complete);
+		priv->xfer_done = true;
+		wake_up(&priv->xfer_wq);
+
 
 		break;
 
@@ -949,7 +975,7 @@  static void nmk_i2c_of_probe(struct device_node *np,
 		priv->sm = I2C_FREQ_MODE_FAST;
 	priv->tft = 1; /* Tx FIFO threshold */
 	priv->rft = 8; /* Rx FIFO threshold */
-	priv->timeout = 200; /* Slave response timeout(ms) */
+	priv->timeout_usecs = 200 * USEC_PER_MSEC; /* Slave response timeout */
 }
 
 static int nmk_i2c_probe(struct amba_device *adev, const struct amba_id *id)
@@ -1009,7 +1035,7 @@  static int nmk_i2c_probe(struct amba_device *adev, const struct amba_id *id)
 	adap->owner = THIS_MODULE;
 	adap->class = I2C_CLASS_DEPRECATED;
 	adap->algo = &nmk_i2c_algo;
-	adap->timeout = msecs_to_jiffies(priv->timeout);
+	adap->timeout = usecs_to_jiffies(priv->timeout_usecs);
 	snprintf(adap->name, sizeof(adap->name),
 		 "Nomadik I2C at %pR", &adev->res);