Re: [RFC PATCH v2 0/2] clk: Support for DT assigned clock parents and rates

[Maxime Coquelin]

Hi Mike,

On 03/21/2014 02:45 AM, Mike Turquette wrote:
> Quoting Sylwester Nawrocki (2014-03-20 05:42:33)
> > Hi Maxime,
> >
> > On 06/03/14 14:45, Maxime Coquelin wrote:
> > > Hi Sylwester,
> > >
> > >        I like the principle of your implementation, but I have two questions:
> > >        1 - How can we manage PM with this solution, as the parent/rate will be
> > > set only once at probe time?
> > >        2 - How to set the parent of a parent clock (which can be shared with
> > > other devices)? Same question about the parent rates.
> >
> > Thanks for your feedback and apologies for late reply.
> >
> > IIUC your first concern is about a situation when clocks need to be
> > reconfigured upon each resume from system sleep or runtime PM resume ?
> > As I mentioned in v1 of the RFC I was considering having individual
> > drivers calling explicitly the clocks set up routine. Presumably this
> > would allow to resolve the power management related issue.
> > One example I'm aware the approach as in this RFC wouldn't work is
> > when a device in a SoC belongs to a power domain, which needs to be
> > first switched on before we can start setting up and the clocks'
> > configuration get lost after the power domain switch off.
>
> I like Sylwester's approach of handling this one-time setup in the
> driver core.
>
> Any kind of fine grained power management should not be hidden by DT,
> and by definition that logic belongs in the device driver. It can still
> be nicely abstracted away by runtime pm[1].
>
> Regards,
> Mike
>
> [1] Message-ID: <20140320114238.GQ7528@xxxxxxxxxxxxxxxxxxxxxx>
How can I access this reference?

Thanks,
Maxime

> > OTOH I suspect devices for which one-time clocks setup is sufficient
> > will be quite common. And for these there would need to be a single
> > call to the setup routine in probe() I guess, since it wouldn't be
> > possible to figure out just from the DT data when the actual call
> > should be made.
> >
> > For a global clocks configuration, I thought about specifying that
> > in the clocks controller node, and then to have the setup routine
> > called e.g. from of_clk_init(). I think that could work well enough,
> > together with the patch [1], adding clock dependencies handling.
> > But then the clock frequency set up function would need to be
> > modified to respect the clock parent relationships, similarly as
> > in patch series [2]. A just noticed [2] recently, after posting
> > this RFC (adding Tero at Cc).
> >
> > --
> > Regards,
> > Sylwester
> >
> > [1] http://www.spinics.net/lists/arm-kernel/msg310507.html
> > [2] http://www.spinics.net/lists/linux-omap/msg103069.html
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