[PATCH v3 1/5] i2c:ocores: stop transfer on timeout

Federico Vaga
2019-02-08T16:12:44Z

Detecting a timeout is ok, but we also need to assert a STOP command on
the bus in order to prevent it from generating interrupts when there are
no on going transfers.

Example: very long transmission.

1. ocores_xfer: START a transfer
2. ocores_isr : handle byte by byte the transfer
3. ocores_xfer: goes in timeout [[bugfix here]]
4. ocores_xfer: return to I2C subsystem and to the I2C driver
5. I2C driver : it may clean up the i2c_msg memory
6. ocores_isr : receives another interrupt (pending bytes to be
transferred) but the i2c_msg memory is invalid now

So, since the transfer was too long, we have to detect the timeout and
STOP the transfer.

Another point is that we have a critical region here. When handling the
timeout condition we may have a running IRQ handler. For this reason I
introduce a spinlock.

In order to make easier to understan locking I have:
- added a new function to handle timeout
- modified the current ocores_process() function in order to be protected
by the new spinlock
Like this it is obvious at first sight that this locking serializes
the execution of ocores_process() and ocores_process_timeout()

Signed-off-by: Federico Vaga <federico.vaga@cern.ch>
---
drivers/i2c/busses/i2c-ocores.c | 54 ++++++++++++++++++++++++++++++++++-------
1 file changed, 45 insertions(+), 9 deletions(-)

diff --git a/drivers/i2c/busses/i2c-ocores.c b/drivers/i2c/busses/i2c-ocores.c
index 87f9caa..aa85202 100644
--- a/drivers/i2c/busses/i2c-ocores.c
+++ b/drivers/i2c/busses/i2c-ocores.c
@@ -25,7 +25,12 @@
#include <linux/slab.h>
#include <linux/io.h>
#include <linux/log2.h>
+#include <linux/spinlock.h>

+/**
+ * @process_lock: protect I2C transfer process.
+ * ocores_process() and ocores_process_timeout() can't run in parallel.
+ */
struct ocores_i2c {
void __iomem *base;
u32 reg_shift;
@@ -36,6 +41,7 @@ struct ocores_i2c {
int pos;
int nmsgs;
int state; /* see STATE_ */
+ spinlock_t process_lock;
struct clk *clk;
int ip_clock_khz;
int bus_clock_khz;
@@ -141,19 +147,26 @@ static void ocores_process(struct ocores_i2c *i2c)
{
struct i2c_msg *msg = i2c->msg;
u8 stat = oc_getreg(i2c, OCI2C_STATUS);
+ unsigned long flags;
+
+ /*
+ * If we spin here is because we are in timeout, so we are going
+ * to be in STATE_ERROR. See ocores_process_timeout()
+ */
+ spin_lock_irqsave(&i2c->process_lock, flags);

if ((i2c->state == STATE_DONE) || (i2c->state == STATE_ERROR)) {
/* stop has been sent */
oc_setreg(i2c, OCI2C_CMD, OCI2C_CMD_IACK);
wake_up(&i2c->wait);
- return;
+ goto out;
}

/* error? */
if (stat & OCI2C_STAT_ARBLOST) {
i2c->state = STATE_ERROR;
oc_setreg(i2c, OCI2C_CMD, OCI2C_CMD_STOP);
- return;
+ goto out;
}

if ((i2c->state == STATE_START) || (i2c->state == STATE_WRITE)) {
@@ -163,7 +176,7 @@ static void ocores_process(struct ocores_i2c *i2c)
if (stat & OCI2C_STAT_NACK) {
i2c->state = STATE_ERROR;
oc_setreg(i2c, OCI2C_CMD, OCI2C_CMD_STOP);
- return;
+ goto out;
}
} else
msg->buf[i2c->pos++] = oc_getreg(i2c, OCI2C_DATA);
@@ -184,14 +197,14 @@ static void ocores_process(struct ocores_i2c *i2c)

oc_setreg(i2c, OCI2C_DATA, addr);
oc_setreg(i2c, OCI2C_CMD, OCI2C_CMD_START);
- return;
+ goto out;
} else
i2c->state = (msg->flags & I2C_M_RD)
? STATE_READ : STATE_WRITE;
} else {
i2c->state = STATE_DONE;
oc_setreg(i2c, OCI2C_CMD, OCI2C_CMD_STOP);
- return;
+ goto out;
}
}

@@ -202,6 +215,9 @@ static void ocores_process(struct ocores_i2c *i2c)
oc_setreg(i2c, OCI2C_DATA, msg->buf[i2c->pos++]);
oc_setreg(i2c, OCI2C_CMD, OCI2C_CMD_WRITE);
}
+
+out:
+ spin_unlock_irqrestore(&i2c->process_lock, flags);
}

static irqreturn_t ocores_isr(int irq, void *dev_id)
@@ -213,9 +229,24 @@ static irqreturn_t ocores_isr(int irq, void *dev_id)
return IRQ_HANDLED;
}

+/**
+ * Process timeout event
+ * @i2c: ocores I2C device instance
+ */
+static void ocores_process_timeout(struct ocores_i2c *i2c)
+{
+ unsigned long flags;
+
+ spin_lock_irqsave(&i2c->process_lock, flags);
+ i2c->state = STATE_ERROR;
+ oc_setreg(i2c, OCI2C_CMD, OCI2C_CMD_STOP);
+ spin_unlock_irqrestore(&i2c->process_lock, flags);
+}
+
static int ocores_xfer(struct i2c_adapter *adap, struct i2c_msg *msgs, int num)
{
struct ocores_i2c *i2c = i2c_get_adapdata(adap);
+ int ret;

i2c->msg = msgs;
i2c->pos = 0;
@@ -225,11 +256,14 @@ static int ocores_xfer(struct i2c_adapter *adap, struct i2c_msg *msgs, int num)
oc_setreg(i2c, OCI2C_DATA, i2c_8bit_addr_from_msg(i2c->msg));
oc_setreg(i2c, OCI2C_CMD, OCI2C_CMD_START);

- if (wait_event_timeout(i2c->wait, (i2c->state == STATE_ERROR) ||
- (i2c->state == STATE_DONE), HZ))
- return (i2c->state == STATE_DONE) ? num : -EIO;
- else
+ ret = wait_event_timeout(i2c->wait, (i2c->state == STATE_ERROR) ||
+ (i2c->state == STATE_DONE), HZ);
+ if (ret == 0) {
+ ocores_process_timeout(i2c);
return -ETIMEDOUT;
+ }
+
+ return (i2c->state == STATE_DONE) ? num : -EIO;
}

static int ocores_init(struct device *dev, struct ocores_i2c *i2c)
@@ -422,6 +456,8 @@ static int ocores_i2c_probe(struct platform_device *pdev)
if (!i2c)
return -ENOMEM;

+ spin_lock_init(&i2c->process_lock);
+
res = platform_get_resource(pdev, IORESOURCE_MEM, 0);
i2c->base = devm_ioremap_resource(&pdev->dev, res);
if (IS_ERR(i2c->base))
--
2.15.0