On 12/03/21 10:34 am, Guenter Roeck wrote: > On 3/11/21 1:17 PM, Chris Packham wrote: >> On 11/03/21 9:18 pm, 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. >>> >> It feels like something like that is happening. Looking at the T2080 >> Reference manual there is an interesting timing diagram (Figure 14-2 if >> someone feels like looking it up). It shows SCL low between the ACK for >> the address and the data byte. I think if we're delayed in sending the >> next byte we could violate Ttimeout or Tlow:mext from the SMBUS spec. >> > I think that really leaves you only two options that I can see: > Rework the driver to handle critical actions (such as setting TXAK, > and everything else that might result in clock stretching) in the > interrupt handler, or rework the driver to handle everything in > a high priority kernel thread. One thing I've found that does seem to avoid the problem is to disable preemption, use polling and replace the schedule() in i2c_wait() with udelay(50). That's kind of like the kernel thread option. > Guenter
