On 03/20/2014 01:42 PM, Sylwester Nawrocki wrote:
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.
No problem! Apologies accepted ;)
IIUC your first concern is about a situation when clocks need to be
reconfigured upon each resume from system sleep or runtime PM resume ?
Yes. This is the case of the STi SoCs.
When resuming from system sleep, the clocks-related registers are
restored at their boot state.
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.
From a functional point of view, that would indeed resolve the PM
related issue.
But I'm not sure that on a performance point of view, parsing the DT at
each driver's resume call is an efficient way.
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.
Yes, that's another case to handle.
I don't know which platforms are in that case, but not STi SoCs for your
information.
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).
OK, I agree with the approach.
There is still the PM issue remaining with these clocks, but I think
that is not related to your series as we already have the issue currently.
Thanks,
Maxime
--
Regards,
Sylwester
[1] http://www.spinics.net/lists/arm-kernel/msg310507.html
[2] http://www.spinics.net/lists/linux-omap/msg103069.html
--
To unsubscribe from this list: send the line "unsubscribe devicetree" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
