On Fri, May 31, 2024 at 04:24:37PM +0200, Stefan Eichenberger wrote: > From: Stefan Eichenberger <stefan.eichenberger@xxxxxxxxxxx> > > On our i.MX8M Mini based module we have an ADS1015 I2C ADC connected to > the I2C bus. The ADS1015 I2C ADC will timeout after 25ms when the I2C > bus is idle. The imx i2c driver will call schedule when waiting for the > bus to become idle after switching to master mode. When the i2c > controller switches to master mode it pulls SCL and SDA low, if the > ADS1015 I2C ADC sees this for more than 25 ms without seeing SCL > clocking, it will timeout and ignore all signals until the next start > condition occurs (SCL and SDA low). Does the I2C specification say anything about this behaviour, or is it specific to this device? > This rfc tries to solve the problem by using a udelay for the first 10 > ms before calling schedule. This reduces the chance that we will > reschedule. However, it is still theoretically possible for the problem > to occur. To properly solve the problem, we would also need to disable > interrupts during the transfer. > > After some internal discussion, we see three possible solutions: > 1. Use udelay as shown in this rfc and also disable the interrupts > during the transfer. This would solve the problem but disable the > interrupts. Also, we would have to re-enable the interrupts if the > timeout is longer than 1ms (TBD). > 2. We use a retry mechanism in the ti-ads1015 driver. When we see a > timeout, we try again. > 3. We use the suggested solution and accept that there is an edge case > where the timeout can happen. 2. has the advantage you fix it for any system with this device, not just those using an IMX. Once question would be, is such a retry safe in all conditions. Does the timeout happen before any non idempotent operation is performed? If the I2C specification allows this behaviour, maybe a more generic solution is needed, since it could affect more devices? Andrew
