Errant readings on LM81 with T2080 SoC

[Guenter Roeck]

On 3/11/21 12:18 AM, Wolfram Sang wrote:
> 
>> Bummer. What is really weird is that you see clock stretching under
>> CPU load. Normally clock stretching is triggered by the device, not
>> by the host.
> 
> One example: Some hosts need an interrupt per byte to know if they
> should send ACK or NACK. If that interrupt is delayed, they stretch the
> clock.
> 

Indeed, the i2c-mpc driver sends TXAK (only) after receiving
that interrupt. Since that is running in the context of the user
process, that may well be delayed substantially on a loaded system.

Maybe the interrupt handler will need to play a more active role
in the i2c-mpc driver. Alternatively, the transfer function could
be handled by a high priority kernel thread.

Guenter

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