On 26/02/24 23:08, Wolfram Sang wrote: > Hey guys, > > we have quite a messy situation regarding I2C timeouts in the dtschema. > Partly because I was too busy to pay detailed attention, partly because > reviewing dtschema changes happen on Github which I totally missed. No > complaining, though, here are my observations and suggestions to get it > straight. Comments are more than welcome. > > - "i2c-transfer-timeout-us" > > Description says "Number of microseconds to wait before considering an > I2C transfer has failed." > > To me, this binding is very descriptive and makes sense. We should keep > it. Sadly, it is the newest one and we already have others. > > > - "i2c-scl-has-clk-low-timeout" > > AFAIU this binding tells that the controller can do clock stretching. > But what for? I don't see why this is important for clients. If > anything, then it would be interesting if the *client* can do clock > stretching and if the controller can actually handle that. But no need > to describe it in DT, we have this as an adapter quirk already > 'I2C_AQ_NO_CLK_STRETCH'. Hmm I know of a few adapters that should probably set I2C_AQ_NO_CLK_STRETCH based on some Errata. Probably just a documentation exercise. It would be nice to reject clients that need to do clock stretching but often it happens as a side effect rather than being intentional (I've seen this with i2c clients implemented in microcontrollers). > Two controllers use it, but no client checks > for it so far. Coming back to this binding, it is also unused in the > kernel. > > Suggestion: let's remove it > > > - "i2c-scl-clk-low-timeout-us" > > The description says "Number of microseconds the clock line needs to be > pulled down in order to force a waiting state." What does "forcing a > waiting state" mean here? I don't understand this description. > > It is used in the i2c-mpc driver. The use case is simply to put it into > the 'struct i2c_adapter.timeout' member. That timeout is used to > determine if a transfer failed. So, to me, "i2c-transfer-timeout-us" > makes a lot more sense to use here. > > Suggestion: let's remove this binding and conver i2c-mpc to > "i2c-transfer-timeout-us". Yes, not nice to have two deprecated > bindings, but things happened. Sounds like a good idea. We'd obviously need to keep support for the existing property but it wouldn't be hard to add "i2c-transfer-timeout-us". I'll try to whip up a patch for that sometime this week, just need to dust off my Freescale boards. > So, these are my thoughts about the current situation. I might have > missed something, so if you have anything to add, I am all ears. > Comments really welcome! > > Happy hacking, > > Wolfram >
