On 2012-11-21 03:56, Alex Courbot wrote: > Hi Tomi, > > On Tuesday 20 November 2012 22:48:18 Tomi Valkeinen wrote: >> I guess there's a reason, but the above looks a bit inconsistent. For >> gpio you define the gpio resource inside the step. For power and pwm the >> resource is defined before the steps. Why wouldn't "pwm = <&pwm 2 >> 5000000>;" work in step2? > > That's mostly a framework issue. Most frameworks do not export a function that > allow to dereference a phandle - they expect resources to be declared right > under the device node and accessed by name through foo_get(device, name). So > using phandles in power sequences would require to export these additional Right, I expected something like that. > functions and also opens the door to some inconsistencies - for instance, your > PWM phandle could be referenced a second time in the sequence with a different > period - how do you know that these are actually referring the same PWM > device? This I didn't understand. Doesn't "<&pwm 2 xyz>" point to a single device, no matter where and how many times it's used? >>> +When a power sequence is run, its steps is executed one after the other >>> until +one step fails or the end of the sequence is reached. >> >> The document doesn't give any hint of what the driver should do if >> running the power sequence fails. Run the "opposite" power sequence? >> Will that work for all resources? I'm mainly thinking of a case where >> each enable of the resource should be matched by a disable, i.e. you >> can't call disable if no enable was called. > > We discussed that issue already (around v5 I think) and the conclusion was > that it should be up to the driver. When we simply enable/disable resources it > is easy to revert, but in the future non-boolean properties will likely be > introduced, and these cannot easily be reverted. Moreover some drivers might > have more complex recovery needs. This deserves more discussion I think, as > I'd like to have some "generic" recovery mechanism that covers most of the > cases. Ok. I'll need to dig up the conversation. Did you consider any examples of how some driver could handle the error cases? What I'm worried about is that, as far as I understand, the power sequence is kinda like black box to the driver. The driver just does "power-up", without knowing what really goes on in there. And if it doesn't know what goes on in there, nor what's in "power-down" sequence, how can it do anything when an error happens? The only option I see is that the driver doesn't do anything, which will leave some resources enabled, or it can run the power-down sequence, which may or may not work. Tomi
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