On 21/03/14 12:20, Maxime Coquelin wrote: > On 03/20/2014 01:42 PM, Sylwester Nawrocki wrote: >> 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. Couldn't this be handled at the clocks controller driver suspend/resume operations ? >> 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. Right, it might not indeed be a good idea to do the parsing repeatedly. >> 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. OK, this could still hopefully be resolved in a clock controller driver, making it aware it belongs to same power domain as the clock consumer devices. >> 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. >> [1] http://www.spinics.net/lists/arm-kernel/msg310507.html >> [2] http://www.spinics.net/lists/linux-omap/msg103069.html -- Regards, Sylwester -- 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
