[PATCH 0/2] omap i2c interrupt handler fixes

[PATCH 0/2] omap i2c interrupt handler fixes

[Alexander Shishkin]

Hi,

This is the second version of the patch that I've sent to linux-omap to
address this issue. This time I've moved the whole errata workaround bit
to a separate function to get rid of too long lines and a couple of extra
levels of indentation.

The actual fix is the same as the first time, it adds a timeout to a busy
loop which happens to take place in an interrupt handler and is capable
of hanging the kernel.

Regards,
--
Alex

[PATCH 1/2] omap i2c: make errata 1.153 workaround a separate function

[Alexander Shishkin]

This is to avoid insanely long lines and levels of indentation.

Signed-off-by: Alexander Shishkin <virtuoso@slind.org>
CC: linux-i2c@vger.kernel.org
CC: linux-omap@vger.kernel.org
---
 drivers/i2c/busses/i2c-omap.c |   43 ++++++++++++++++++++++------------------
 1 files changed, 24 insertions(+), 19 deletions(-)

diff --git a/drivers/i2c/busses/i2c-omap.c b/drivers/i2c/busses/i2c-omap.c
index 75bf3ad..ad8242a 100644
--- a/drivers/i2c/busses/i2c-omap.c
+++ b/drivers/i2c/busses/i2c-omap.c
@@ -671,6 +671,27 @@ omap_i2c_rev1_isr(int this_irq, void *dev_id)
 #define omap_i2c_rev1_isr		NULL
 #endif
 
+/*
+ * OMAP3430 Errata 1.153: When an XRDY/XDR is hit, wait for XUDF before writing
+ * data to DATA_REG. Otherwise some data bytes can be lost while transferring
+ * them from the memory to the I2C interface.
+ */
+static int omap3430_workaround(struct omap_i2c_dev *dev, u16 *stat, int *err)
+{
+	while (!(*stat & OMAP_I2C_STAT_XUDF)) {
+		if (*stat & (OMAP_I2C_STAT_NACK | OMAP_I2C_STAT_AL)) {
+			omap_i2c_ack_stat(dev, *stat & (OMAP_I2C_STAT_XRDY |
+							OMAP_I2C_STAT_XDR));
+			*err |= OMAP_I2C_STAT_XUDF;
+			return -1;
+		}
+		cpu_relax();
+		*stat = omap_i2c_read_reg(dev, OMAP_I2C_STAT_REG);
+	}
+
+	return 0;
+}
+
 static irqreturn_t
 omap_i2c_isr(int this_irq, void *dev_id)
 {
@@ -794,25 +815,9 @@ complete:
 					break;
 				}
 
-				/*
-				 * OMAP3430 Errata 1.153: When an XRDY/XDR
-				 * is hit, wait for XUDF before writing data
-				 * to DATA_REG. Otherwise some data bytes can
-				 * be lost while transferring them from the
-				 * memory to the I2C interface.
-				 */
-
-				if (dev->rev <= OMAP_I2C_REV_ON_3430) {
-						while (!(stat & OMAP_I2C_STAT_XUDF)) {
-							if (stat & (OMAP_I2C_STAT_NACK | OMAP_I2C_STAT_AL)) {
-								omap_i2c_ack_stat(dev, stat & (OMAP_I2C_STAT_XRDY | OMAP_I2C_STAT_XDR));
-								err |= OMAP_I2C_STAT_XUDF;
-								goto complete;
-							}
-							cpu_relax();
-							stat = omap_i2c_read_reg(dev, OMAP_I2C_STAT_REG);
-						}
-				}
+				if (dev->rev <= OMAP_I2C_REV_ON_3430 &&
+				    omap3430_workaround(dev, &stat, &err))
+					goto complete;
 
 				omap_i2c_write_reg(dev, OMAP_I2C_DATA_REG, w);
 			}
-- 
1.6.3.3

[PATCH 1/2] omap i2c: make errata 1.153 workaround a separate function

[Alexander Shishkin]

From: Alexander Shishkin <ext-alexander.shishkin@nokia.com>

This is to avoid insanely long lines and levels of indentation.

Signed-off-by: Alexander Shishkin <ext-alexander.shishkin@nokia.com>
---
 drivers/i2c/busses/i2c-omap.c |   43 ++++++++++++++++++++++------------------
 1 files changed, 24 insertions(+), 19 deletions(-)

diff --git a/drivers/i2c/busses/i2c-omap.c b/drivers/i2c/busses/i2c-omap.c
index 75bf3ad..ad8242a 100644
--- a/drivers/i2c/busses/i2c-omap.c
+++ b/drivers/i2c/busses/i2c-omap.c
@@ -671,6 +671,27 @@ omap_i2c_rev1_isr(int this_irq, void *dev_id)
 #define omap_i2c_rev1_isr		NULL
 #endif
 
+/*
+ * OMAP3430 Errata 1.153: When an XRDY/XDR is hit, wait for XUDF before writing
+ * data to DATA_REG. Otherwise some data bytes can be lost while transferring
+ * them from the memory to the I2C interface.
+ */
+static int omap3430_workaround(struct omap_i2c_dev *dev, u16 *stat, int *err)
+{
+	while (!(*stat & OMAP_I2C_STAT_XUDF)) {
+		if (*stat & (OMAP_I2C_STAT_NACK | OMAP_I2C_STAT_AL)) {
+			omap_i2c_ack_stat(dev, *stat & (OMAP_I2C_STAT_XRDY |
+							OMAP_I2C_STAT_XDR));
+			*err |= OMAP_I2C_STAT_XUDF;
+			return -1;
+		}
+		cpu_relax();
+		*stat = omap_i2c_read_reg(dev, OMAP_I2C_STAT_REG);
+	}
+
+	return 0;
+}
+
 static irqreturn_t
 omap_i2c_isr(int this_irq, void *dev_id)
 {
@@ -794,25 +815,9 @@ complete:
 					break;
 				}
 
-				/*
-				 * OMAP3430 Errata 1.153: When an XRDY/XDR
-				 * is hit, wait for XUDF before writing data
-				 * to DATA_REG. Otherwise some data bytes can
-				 * be lost while transferring them from the
-				 * memory to the I2C interface.
-				 */
-
-				if (dev->rev <= OMAP_I2C_REV_ON_3430) {
-						while (!(stat & OMAP_I2C_STAT_XUDF)) {
-							if (stat & (OMAP_I2C_STAT_NACK | OMAP_I2C_STAT_AL)) {
-								omap_i2c_ack_stat(dev, stat & (OMAP_I2C_STAT_XRDY | OMAP_I2C_STAT_XDR));
-								err |= OMAP_I2C_STAT_XUDF;
-								goto complete;
-							}
-							cpu_relax();
-							stat = omap_i2c_read_reg(dev, OMAP_I2C_STAT_REG);
-						}
-				}
+				if (dev->rev <= OMAP_I2C_REV_ON_3430 &&
+				    omap3430_workaround(dev, &stat, &err))
+					goto complete;
 
 				omap_i2c_write_reg(dev, OMAP_I2C_DATA_REG, w);
 			}
-- 
1.6.3.3

[PATCH 2/2] omap i2c: add a timeout to the busy waiting

[Alexander Shishkin]

The errata 1.153 workaround is busy waiting on XUDF bit in interrupt
context, which may lead to kernel hangs. The problem can be reproduced
by running the bus with wrong (too high) speed.

Signed-off-by: Alexander Shishkin <virtuoso-0lOfPCoBze7YtjvyW6yDsg@public.gmane.org>
CC: linux-i2c-u79uwXL29TY76Z2rM5mHXA@public.gmane.org
CC: linux-omap-u79uwXL29TY76Z2rM5mHXA@public.gmane.org
---
 drivers/i2c/busses/i2c-omap.c |    7 ++++++-
 1 files changed, 6 insertions(+), 1 deletions(-)

diff --git a/drivers/i2c/busses/i2c-omap.c b/drivers/i2c/busses/i2c-omap.c
index ad8242a..b474c20 100644
--- a/drivers/i2c/busses/i2c-omap.c
+++ b/drivers/i2c/busses/i2c-omap.c
@@ -678,7 +678,9 @@ omap_i2c_rev1_isr(int this_irq, void *dev_id)
  */
 static int omap3430_workaround(struct omap_i2c_dev *dev, u16 *stat, int *err)
 {
-	while (!(*stat & OMAP_I2C_STAT_XUDF)) {
+	unsigned long timeout = 10000;
+
+	while (!(*stat & OMAP_I2C_STAT_XUDF && --timeout)) {
 		if (*stat & (OMAP_I2C_STAT_NACK | OMAP_I2C_STAT_AL)) {
 			omap_i2c_ack_stat(dev, *stat & (OMAP_I2C_STAT_XRDY |
 							OMAP_I2C_STAT_XDR));
@@ -689,6 +691,9 @@ static int omap3430_workaround(struct omap_i2c_dev *dev, u16 *stat, int *err)
 		*stat = omap_i2c_read_reg(dev, OMAP_I2C_STAT_REG);
 	}
 
+	if (!timeout)
+		dev_err(dev->dev, "timeout waiting on XUDF bit\n");
+
 	return 0;
 }
 
-- 
1.6.3.3

Re: [PATCH 1/2] omap i2c: make errata 1.153 workaround a separate function

[Alexander Shishkin]

On Wed, Dec 16, 2009 at 03:43:04 +0200, Alexander Shishkin wrote:
> From: Alexander Shishkin <ext-alexander.shishkin@nokia.com>

Please disregard this, I've got the emails wrong here. I'll resend
shortly.

Regards,
--
Alex