Hi Lee, > > It looks like a workaround to me. It would be interesting to hear which > > I2C client breaks with DMA and if it's driver can't be fixed somehow > > instead. But even if we agree on a workaround short term, adding a So, are there investigations running why this reboot happens? > > Is there no other way to disable DMA which is local to this driver so we > > can easily revert the workaround later? > > This is the most local low-impact solution (nomenclature aside). I disagree. You could use of_machine_is_compatible() and disable DMA for that machine. Less impact because we save the workaround binding. > The beautiful thing about this approach is that, *if* the Geni SE DMA I'd say 'advantage' instead of 'beautiful' ;) > ever starts working, we can remove the C code and any old properties > left in older DTs just become NOOP. Older kernels with newer DTs > (less of a priority) *still* won't work, but they don't work now > anyway. Which is a clear disadvantage of that solution. It won't fix older kernels. My suggestion above should fix them, too. > The offending line can be found at [0]. There is no obvious bug to > fix and this code obviously works well on some of the hardware > platforms using it. But on our platform (Lenovo Yoga C630 - QCom > SMD850) that final command, which initiates the DMA transaction, ends > up rebooting the machine. Unless we know why the reboot happens on your platform, I'd be careful with saying "work obviously well" on other platforms. > With regards to the nomenclature, my original suggestion was > 'qcom,geni-se-no-dma'. Would that better suit your request? My suggestion: For 5.3, use of_machine_is_compatible() and we backport that. For later, try to find out the root cause and fix it. If that can't be done, try to set up a generic "disable-dma" property and use it. What do you think about that? Kind regards, Wolfram
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