diff mbox

[1/3] i2c: bcm2835: Fix hang for writing messages larger than 16 bytes

Message ID 1474298777-5858-1-git-send-email-noralf@tronnes.org (mailing list archive)
State New, archived
Headers show

Commit Message

Noralf Trønnes Sept. 19, 2016, 3:26 p.m. UTC
Writing messages larger than the FIFO size results in a hang, rendering
the machine unusable. This is because the RXD status flag is set on the
first interrupt which results in bcm2835_drain_rxfifo() stealing bytes
from the buffer. The controller continues to trigger interrupts waiting
for the missing bytes, but bcm2835_fill_txfifo() has none to give.
In this situation wait_for_completion_timeout() apparently is unable to
stop the madness.

The BCM2835 ARM Peripherals datasheet has this to say about the flags:
  TXD: is set when the FIFO has space for at least one byte of data.
  RXD: is set when the FIFO contains at least one byte of data.
  TXW: is set during a write transfer and the FIFO is less than full.
  RXR: is set during a read transfer and the FIFO is or more full.

Implementing the logic from the downstream i2c-bcm2708 driver solved
the hang problem.

Signed-off-by: Noralf Trønnes <noralf@tronnes.org>
---
 drivers/i2c/busses/i2c-bcm2835.c | 22 ++++++++++++++--------
 1 file changed, 14 insertions(+), 8 deletions(-)

Comments

Eric Anholt Sept. 19, 2016, 4:51 p.m. UTC | #1
Noralf Trønnes <noralf@tronnes.org> writes:

> Writing messages larger than the FIFO size results in a hang, rendering
> the machine unusable. This is because the RXD status flag is set on the
> first interrupt which results in bcm2835_drain_rxfifo() stealing bytes
> from the buffer. The controller continues to trigger interrupts waiting
> for the missing bytes, but bcm2835_fill_txfifo() has none to give.
> In this situation wait_for_completion_timeout() apparently is unable to
> stop the madness.
>
> The BCM2835 ARM Peripherals datasheet has this to say about the flags:
>   TXD: is set when the FIFO has space for at least one byte of data.
>   RXD: is set when the FIFO contains at least one byte of data.
>   TXW: is set during a write transfer and the FIFO is less than full.
>   RXR: is set during a read transfer and the FIFO is or more full.
>
> Implementing the logic from the downstream i2c-bcm2708 driver solved
> the hang problem.
>
> Signed-off-by: Noralf Trønnes <noralf@tronnes.org>

Patches 1, 3 are:

Reviewed-by: Eric Anholt <eric@anholt.net>

For patch 2 I followed some of it, but couldn't quite say it's a review.
I trust your testing, and that the path has had a lot more testing in
the downstream tree, so it's:

Acked-by: Eric Anholt <eric@anholt.net>

Thanks!
Noralf Trønnes Sept. 19, 2016, 5:36 p.m. UTC | #2
Den 19.09.2016 18:51, skrev Eric Anholt:
> Noralf Trønnes <noralf@tronnes.org> writes:
>
>> Writing messages larger than the FIFO size results in a hang, rendering
>> the machine unusable. This is because the RXD status flag is set on the
>> first interrupt which results in bcm2835_drain_rxfifo() stealing bytes
>> from the buffer. The controller continues to trigger interrupts waiting
>> for the missing bytes, but bcm2835_fill_txfifo() has none to give.
>> In this situation wait_for_completion_timeout() apparently is unable to
>> stop the madness.
>>
>> The BCM2835 ARM Peripherals datasheet has this to say about the flags:
>>    TXD: is set when the FIFO has space for at least one byte of data.
>>    RXD: is set when the FIFO contains at least one byte of data.
>>    TXW: is set during a write transfer and the FIFO is less than full.
>>    RXR: is set during a read transfer and the FIFO is or more full.
>>
>> Implementing the logic from the downstream i2c-bcm2708 driver solved
>> the hang problem.
>>
>> Signed-off-by: Noralf Trønnes <noralf@tronnes.org>
> Patches 1, 3 are:
>
> Reviewed-by: Eric Anholt <eric@anholt.net>
>
> For patch 2 I followed some of it, but couldn't quite say it's a review.
> I trust your testing, and that the path has had a lot more testing in
> the downstream tree, so it's:

I don't know how much testing downstream really has had since this feature
is disabled by default. So there is a possibility that this can break some
devices (while at the same time enable others).
I wondered about adding a module parameter so it could be disabled at
runtime, but decided to see what the review would be first.
It is of course possible to add a this module parameter later should it
turn out to break some device.

Noralf.

> Acked-by: Eric Anholt <eric@anholt.net>
>
> Thanks!
Martin Sperl Sept. 20, 2016, 6:46 a.m. UTC | #3
On 19.09.2016 17:26, Noralf Trønnes wrote:
> Writing messages larger than the FIFO size results in a hang, rendering
> the machine unusable. This is because the RXD status flag is set on the
> first interrupt which results in bcm2835_drain_rxfifo() stealing bytes
> from the buffer. The controller continues to trigger interrupts waiting
> for the missing bytes, but bcm2835_fill_txfifo() has none to give.
I remember having seen similar interrupt issues with the SPI HW-block.
> In this situation wait_for_completion_timeout() apparently is unable to
> stop the madness.
That is because it is a level irq that immediately triggers another 
interrupt giving
no CPU no time to do other (threaded) OS activity - this might be slightly
different for multi-core machines...
> The BCM2835 ARM Peripherals datasheet has this to say about the flags:
>    TXD: is set when the FIFO has space for at least one byte of data.
>    RXD: is set when the FIFO contains at least one byte of data.
>    TXW: is set during a write transfer and the FIFO is less than full.
>    RXR: is set during a read transfer and the FIFO is or more full.
>
> Implementing the logic from the downstream i2c-bcm2708 driver solved
> the hang problem.
>
> Signed-off-by: Noralf Trønnes<noralf@tronnes.org>
Reviewed-by: Martin Sperl <kernel@martin.sperl.org>
diff mbox

Patch

diff --git a/drivers/i2c/busses/i2c-bcm2835.c b/drivers/i2c/busses/i2c-bcm2835.c
index d4f3239..f283b71 100644
--- a/drivers/i2c/busses/i2c-bcm2835.c
+++ b/drivers/i2c/busses/i2c-bcm2835.c
@@ -64,6 +64,7 @@  struct bcm2835_i2c_dev {
 	int irq;
 	struct i2c_adapter adapter;
 	struct completion completion;
+	struct i2c_msg *curr_msg;
 	u32 msg_err;
 	u8 *msg_buf;
 	size_t msg_buf_remaining;
@@ -126,14 +127,13 @@  static irqreturn_t bcm2835_i2c_isr(int this_irq, void *data)
 		return IRQ_HANDLED;
 	}
 
-	if (val & BCM2835_I2C_S_RXD) {
-		bcm2835_drain_rxfifo(i2c_dev);
-		if (!(val & BCM2835_I2C_S_DONE))
-			return IRQ_HANDLED;
-	}
-
 	if (val & BCM2835_I2C_S_DONE) {
-		if (i2c_dev->msg_buf_remaining)
+		if (i2c_dev->curr_msg->flags & I2C_M_RD) {
+			bcm2835_drain_rxfifo(i2c_dev);
+			val = bcm2835_i2c_readl(i2c_dev, BCM2835_I2C_S);
+		}
+
+		if ((val & BCM2835_I2C_S_RXD) || i2c_dev->msg_buf_remaining)
 			i2c_dev->msg_err = BCM2835_I2C_S_LEN;
 		else
 			i2c_dev->msg_err = 0;
@@ -141,11 +141,16 @@  static irqreturn_t bcm2835_i2c_isr(int this_irq, void *data)
 		return IRQ_HANDLED;
 	}
 
-	if (val & BCM2835_I2C_S_TXD) {
+	if (val & BCM2835_I2C_S_TXW) {
 		bcm2835_fill_txfifo(i2c_dev);
 		return IRQ_HANDLED;
 	}
 
+	if (val & BCM2835_I2C_S_RXR) {
+		bcm2835_drain_rxfifo(i2c_dev);
+		return IRQ_HANDLED;
+	}
+
 	return IRQ_NONE;
 }
 
@@ -155,6 +160,7 @@  static int bcm2835_i2c_xfer_msg(struct bcm2835_i2c_dev *i2c_dev,
 	u32 c;
 	unsigned long time_left;
 
+	i2c_dev->curr_msg = msg;
 	i2c_dev->msg_buf = msg->buf;
 	i2c_dev->msg_buf_remaining = msg->len;
 	reinit_completion(&i2c_dev->completion);