CCing Marek Vasut and Pengutronix... On Thu, Jun 27, 2013 at 07:39:45PM +0200, Torsten Fleischer wrote: > Hi, > > on my board there is a temperature sensor TCN75A (compatible to LM75) > connected to the iMX283. > In the user space the temperature is periodically polled by reading the file > /sys/bus/i2c/devices/0-0048/temp1_input. > When triggering this file the LM75 driver consecutively reads 3 registers from > the sensor and outputs the current temperature read from register 0. > > With linux 3.9.7 I sometimes get a communication timeout when reading the > sensor. > > Since several patches have been added to the driver, I tried linux 3.10-rc7. > With this version no timeout will be reported, but sometimes the value > returned seems to be wrong. Normally I get a value of round about 30000. But > sometimes it takes some seconds to read the temperature and the returned value > is 75000. This value is not the current temperature but the temperature > hysteresis that is the content of register 2 of the sensor. > > After some investigation I found that the i2c-mxs driver sometimes times out > while waiting for the MXS_I2C_DEBUG0_DMAREQ bit when writing data (the > I2C_M_RD flag is not set). > Unfortunately this error is never reported to the I2C core and thus to the > LM75 driver. So the LM75 driver assumes that it has received the correct > values. > > This problem seems to be only in the PIO mode. After changing the driver so > that the DMA is always used it works as expected. > > Best regards, > Torsten Fleischer > -- > To unsubscribe from this list: send the line "unsubscribe linux-i2c" in > the body of a message to majordomo@xxxxxxxxxxxxxxx > More majordomo info at http://vger.kernel.org/majordomo-info.html
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