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
