On 3/17/21 8:46 PM, Chris Packham wrote: > > 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. > I've made some reasonable progress on making i2c-mpc more interrupt > driven. Assuming it works out for my use-case is there an opinion on > making interrupt support mandatory? Looking at all the in-tree dts files > that use one of the compatible strings from i2c-mpc.c they all have > interrupt properties so in theory nothing is using the polling mode. But > there may be some out-of-tree boards or boards using an old dtb that > would be affected? > The polling code is from pre-git times. Like 2005 and earlier. I'd say it is about time to get rid of it. Any out-of-tree users had more than 15 years to upstream their code, after all. Guenter
