Grygorii, thanks a lot for your input. Much appreciated! > That would be great, but note: > 1) only i2c_transfer() operations are locked, so if driver is doing > i2c_transfer(1) > i2c_transfer(2) <- suspend in the middle > <- suspend in between > i2c_transfer(3) > It will not help. Will it not improve the situation by ensuring that at least the transfer with its (potenitally) multiple messages got completed? That we are at least in a bus-free state (assuming single-master here) before suspending? > Everything depends on timings :( - in my practice 10000 suspend iteration tests > where required to run many times to catch 3 buggy I2C client drivers. Matches my experiences that creating a reliable test case for that is not that easy as I thought. Or I am missing something obvious. > 2) It's normal to abort suspend if system is busy, so if I2C core will be able > to catch active I2C operation - it should abort, but again I do not see how it > can be detected 100% with current I2C core design or without reworking huge number of drivers. I agree. After second thought, waiting for i2c_transfer to finish maybe won't be enough, I am afraid. We don't know if STOP has been put on the wires yet. My best bet now is that we implement such a 'is-transfer-ongoing'-check in the suspend function of the master driver? That check should be optional, but recommended. > 3) So, only one thing I2C core potentially can do - catch invalid access and > report it. "wait for transfer to finish" wouldn't work as for me. And we do this in suspend_noirq function of the i2c core. > > I at least know of some Renesas boards which needed the I2C connected > > PMIC to do a system reset (not sure about suspend, need to recheck > > that). That still today causes problems because interrupts are disabled > > then. > > this was triggered few times already (sry, don't have links), as of now, > and as I know, the only ways to W/A this is: > - to create barametal platform driver (some time in ASM) > - or delegate final suspend operation to another system controller (co-processor), > as example TI am335x SoCs, > - or implement I2C driver in hw - TI AVS/SmartReflex. Yes. Please note that this is only needed for reset, not suspend. So, it is a bit easier. Still, it might make more sense to use a platform based solution. I'll think about that. > Sry, but 99% percent of I2C client drivers *should not* access I2C bus after > .suspend_noirq() stage it's BUG-BUG!! Any W/A will just hide real problems. I do believe you, still is there documentation about such things? I like to understand more but didn't dig up something up to now. E.g. I grepped for "noirq" in Documentation/power. > "master_xfer_irqless" might be a not bad idea, but, in my opinion, it > should be used explicitly by platform code only, and each usage should > be proved to exist. Yes, we can think about it once it is really needed. > Some additional info: Thanks a lot for that! > I'm attaching some very old patch (don't ask me why it was not sent :() > I did for Android system - which likes suspend very much. Some > part of below diff are obsolete now (like omap_i2c_suspend()), > but .noirq() callback are still valid and can show over all idea. > Really helped to catch min 3 buggy client drivers with timers, delayed > or periodic works. Ok, so what do you think about my plan to: 1) encourage drivers to check if there is still an ongoing transfer in their .suspend function (or the core can do that, too, if we agree that checking for a taken adapter lock is sufficient) -> to ensure transfers don't get interrupted in the middle 2) use a .suspend_noirq callback in i2c_bus_type.pm to reject and WARN about transfers still going on in that phase -> this ensures that buggy drivers are caught 3) write some documentation about our findings / assumptions / recommendations to a file in Documentation/i2c/ -> this ensures we won't forget why we did things like they are ;) ? Kind regards, Wolfram
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