i2c driver debugging on low memory

[Pankaj Pandey]

Hi All, 

We are trying to use Goodix GT-911 touch sensor with synopsis DW-I2C IP to configure the sensor. The I2c driver is interrupt driven and the depth of Receive/transmit FIFO is 32-bytes. During the probe of GT-911 touch sensor, The sensor requests the firmware using request_firmware_nowait() call which uses system workqueue thread for the call-back function, if the firmware is found successfully. The touch sensor is compiled as a part of the kernel and not as a separate module. The issue is that when the call back function is called from the workqueue thread (kworker/0:1) and it tries to send the 186 bytes of firmware that it has found, The I2C_TX_EMPTY interrupt (I2C TX Threshold = 16 bytes) is getting delayed for several milliseconds. When the same data is sent through the main probing thread (swapper) during the system init, we can see the I2C_TX_EMPTY interrupt is not delayed and the whole 186 byte of firmware is sent through successfully in a single burst.   Due to the delaying of the I2C interrupt handling in workqueue thread, the data that should have been replenished in the TX FIFO after the I2C_TX_EMPTY interrupt was not replenished, and the I2C STOP was detected. This I2C stop is used in the ISR of DW-I2C handler to release a completion, which is being waited upon in the i2c_dw_xfer (master_xfer) function. This causes the I2C transfer to terminate abnormally resulting in the failure of Goodix Probe. 

Any pointer how we can debug this issue?  We are booting linux-5.4 xip boot which is booting on a small memory system which is about 8mb mram. We tried PERF or FTRACE results in OOM Killer during the device init itself (verified through the log_buf).

Regards,

Pankaj Pandey

[Kaiwan N Billimoria]

Hi Pankaj,

Don't know if this will help, but have you tried passing the @gfp param of request_firmware_nowait() as GFP_ATOMIC (as opposed to GFP_KERNEL)?

The func header states that this ensures it "can't sleep at all"..

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[Pankaj Pandey]

Thanks Kaiwan, will try GFP_ATOMIC.

Regards,

Pankaj Pandey