Hi Hein, Felipe
On 07/16/2013 12:42 PM, Felipe Balbi wrote:
Hi,
On Tue, Jul 16, 2013 at 05:33:47PM +0800, Hein Tibosch wrote:
On 7/16/2013 5:03 PM, Felipe Balbi wrote:
Hi,
On Tue, Jul 16, 2013 at 04:19:35PM +0800, Hein Tibosch wrote:
Hi Vikram,
On a OMAP4460, i2c-bus-3:
A driver (lm75) is causing many 'timeout waiting for bus ready' errors.
SDA remains high (as it should), but SCL remains low after a NACK.
The bus becomes _unusable for other clients_.
While probing, "lm75" writes a command, followed by a read + stop,
but the write command is NACK'd. The chip does accept other writes/reads,
it just refuses to ack invalid commands.
Can you tell me if the patch below would make any sense? Or is it the
responsibility of the client to reset the i2c_smbus?
patch below breaks repeated start.
Felipe, I'd very appreciate if you'd be able to provide the use case
which will fail with such solution?
Hi,
No, after the NACK, no more commands are being processed,
including a repeated start. omap_i2c_xfer() returns -EREMOTEIO
without ever freeing the bus.
The bus is left in an impossible state with SCL constantly low
and all next commands (to different chips) will therefore get
a -ETIMEDOUT
With this patch, the bus will become idle again and new commands
can be processed normally
I think, this is valid fix, but it was done here already:)
http://patchwork.ozlabs.org/patch/249790/
"i2c: omap: query STP always when NACK is received"
And nacked in the same way :(
But! I've back-ported my patch on TI Android product kernel 3.4, did
sanity test and I didn't see any issues with my patch :))
but you mentioned that if you have IGNORE_NAK set, everything is fine,
since lm75 will get a return value of 0 and things will work just fine,
right ?
Also, you also said that the chip 'refuses to ack invalid commands', why
are you sending invalid commands to start with ? This could be a bug in
i2c-omap.c, sure, but let's try to figure out why IGNORE_NAK helps and
why is lm75 driver sending invalid commands.
The problem is, that lm75 device is SmBus compatible and its driver has
.detect() function implemented. During detection it tries to scan some
registers which might be not present in current device - in my case
it's tmp105.
For example to read regA in tmp105 following is done:
1) do write in "Index" register (val RegA index) (I2C 1st message)
2) do read (I2C 2d message)
the message 1 is Nacked by device in case if register index is wrong,
but i2c-omap don't send NACK (or STP). As result, bus stack in Bus Busy
state.
For SMBus devices the specification states (http://smbus.org/specs/)
"4.2.Acknowledge (ACK) and not acknowledge (NACK)":
- "The slave device detects an invalid command or invalid data. In this
case the slave device must not acknowledge the received byte. The
master upon detection of this condition must generate a STOP condition
and retry the transaction"
Regards,
-grygorii
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