On 07/31/2012 09:22 PM, 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.
Using nodes has a big advantage though: we can use any arbitrary
property to add extra parameters to the resource being controlled. Right
now we only use enable/disable, but for example one can imagine an
optional voltage setting for a regulator. It is much more future-proof
than a design where the number of parameters would be fixed and could
not be extended without breaking compatibility.
I experimented encoding the whole sequence within a single property. It
works of course, but is not really flexible, hard to read, and quite
error-prone overall. The memory footprint gain was not so obvious
neither (although it was indeed more compact).
What bothers me is to have to specify the cells layout and reg property
for *every single sequence*, but well, I guess we can live with that.
Alex.
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