Re: [RFC][PATCH v3 1/3] runtime interpreted power sequences

[Alex Courbot]

On 07/31/2012 09:55 PM, Mitch Bradley wrote:
> On 7/31/2012 8:38 PM, Thierry Reding wrote:
> > On Tue, Jul 31, 2012 at 08:22:17PM +0800, Mitch Bradley wrote:
> > > On 7/31/2012 6:56 PM, Thierry Reding wrote:
> > > > On Tue, Jul 31, 2012 at 07:32:20PM +0900, Alex Courbot wrote:
> > > > > On 07/31/2012 07:45 AM, Stephen Warren wrote:
> > > > > > I wonder if using the same structure/array as input and output would
> > > > > > simplify the API; the platform data would fill in the fields mentioned
> > > > > > above, and power_seq_build() would parse those, then set other fields in
> > > > > > the same structs to the looked-up handle values?
> > > > >
> > > > > The thing is that I am not sure what happens to the platform data
> > > > > once probe() is done. Isn't it customary to mark it with __devinit
> > > > > and have it freed after probing is successful?
> > > >
> > > > No, platform data should stay around forever. Otherwise, consider what
> > > > would happen if your driver is built as a module and you unload and load
> > > > it again.
> > > >
> > > > > More generally, I think it is a good practice to have data
> > > > > structures tailored right for what they need to do - code with
> > > > > members that are meaningful only at given points of an instance's
> > > > > life tends to be more confusing.
> > > >
> > > > I agree. Furthermore the driver unload/reload would be another reason
> > > > not to reuse platform data as the output of the build() function.
> > > >
> > > > But maybe what Stephen meant was more like filling a structure with data
> > > > taken from the platform data and pass that to a resolve() function which
> > > > would fill in the missing pieces like pointers to actual resources. I
> > > > imagine a managed interface would become a little trickier to do using
> > > > such an approach.
> > > >
> > > > > > If the nodes have a unit address (i.e. end in "@n"), which they will
> > > > > > have to if all named "step" and there's more than one of them, then they
> > > > > > will need a matching reg property. Equally, the parent node will need
> > > > > > #address-cells and #size-cells too. So, the last couple lines would be:
> > > > > >
> > > > > > 		power-on-sequence {
> > > > > > 			#address-cells = <1>;
> > > > > > 			#size-cells = <0>;
> > > > > > 			step@0 {
> > > > > > 				reg = <0>;
> > > > >
> > > > > That's precisely what I would like to avoid - I don't need the steps
> > > > > to be numbered and I certainly have no use for a reg property. Isn't
> > > > > there a way to make it simpler?
> > > >
> > > > It's not technically valid to not have the reg property. Or
> > > > #address-cells and #size-cells properties for that matter.
> > >
> > > I'm not keen on this representation where individual steps are nodes.
> > > That seems like it could end up being too "heavyweight" for a long sequence.
> >
> > The other alternative would involve using a single property to encode
> > one sequence. I think that was the initial proposal, though using proper
> > phandle encoding it could probably be enhanced a bit. However anything
> > that involves a single property has the problem that we need to encode
> > the type of resource as an integer, and that makes things very hard to
> > read.
> >
> > So it would look something like this:
> >
> > 	power-on = <1  &gpio 6 0            1
> > 		    0                   10000
> > 		    2  &reg                 1
> > 		    3  &pwm  0 5000000      1>;
> >
> > 	power-off = <3  &pwm  0 5000000      0
> > 		     2  &reg                 0
> > 		     0                   10000
> > 		     1  &gpio 6 0            0>;
> >
> > So the first cell would encode the type:
> >    0: delay
> >    1: gpio
> >    2: regulator
> >    3: PWM
> >
> > The next n cells would be the phandle and the specifier, while the last
> > cell would encode a resource-specific parameter:
> >    delay: time in microseconds
> >    gpio: set level (0: low, 1: high)
> >    regulator: 0: disable, 1: enable
> >    pwm: 0: disable, 1: enable
> >
> > I guess this would be more compact, but it is also very hard to read. Is
> > that something you would be happier with? Perhaps you were thinking of
> > something completely different?
>
>
> Perhaps a compact/flexible encoding could be designed, with a textual
> encoding that is easy to read.  A separate tool could convert the text
> encoding to the integer format, annotated with comments containing
> the "source text".  A file containing that output could be #included
> into the dts file.

Do you mean having a external compiler that would run before dtc just 
for producing the power sequences? That sounds a little bit overkill for 
something that ough to remain simple.

Also, although I admit I don't have the whole picture of where they 
could be used, I don't expect the power sequences to grow to sizes that 
would make us bother about their footprint.

Alex.

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