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. > 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 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. -- balbi
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