On Sat, 8 Aug 2009, Magnus Damm wrote: > On Fri, Aug 7, 2009 at 11:32 PM, Alan Stern<stern@xxxxxxxxxxxxxxxxxxx> wrote: > > On Fri, 7 Aug 2009, Magnus Damm wrote: > > > >> PM: Runtime PM v13 for Platform Devices 20090807 > >> > >> [PATCH 01/05] PM: Runtime PM v13 - add dev_pm_ops helpers > > > > This patch doesn't do anything much, besides reverting a change I asked > > Rafael to make. I don't see how it helps platform-specific code do > > anything. > > It's helping different bus types to implement the runtime part of the > dev_pm_ops in a consistent way. I suggest that all bus types should > return -ENOSYS if the callback is missing. Doesn't Rafael's code already do this? > And they can do so by using > the helper functions. The change is not platform specific, but my > latest SuperH platform Runtime PM prototype makes use of it. > > The latest SuperH specific Runtime PM implementation require > dev_pm_ops even though there is no work to be done for the driver. The > code works in a sort of opt-in way at this point, so callbacks are > explicitly required. I'd like us to standardize on this behaviour if > possible, so runtime pm enabled platform drivers can be shared between > different platform bus implementations. So my LCDC platform driver > will work fine on both SuperH SoCs and ARM SoCs. I still don't see the connection. Why are helper functions useful? > Sorry for reverting your change, but I couldn't see any clear benefit > with the v11->v13 lock-drop-inside-the-if-case change. Isn't it just > avoiding dropping the lock in the uncommon error case? Maybe I'm > misunderstanding. Basically you are right, except for one thing: The error case might not be so uncommon. That's the benefit. Rafael, along these lines, I suspect we might not want to go into an error state if a runtime suspend fails because there is no callback function. Returning -ENOSYS to the caller is fine, but leave runtime_error set to 0. Maybe do the same for runtime resume. > >> [PATCH 02/05] PM: Runtime PM v13 - let bus-less devices succeed > > > > This could be added without 01/05. But why do you want it? Busless > > devices don't have PM runtime callbacks, so whether the core thinks the > > callbacks succeed or not doesn't make any difference. > > > > You say that "Runtime suspend and resume of devices on the platform bus > > is impossible without this change", but you don't explain why -- or why > > the patch makes runtime suspend and resume of these devices possible. > > Right now, in the standard upstream kernel all platform devices get > assigned a parent device unless one exists are registration time. The > shared parent device is parent-less. Since the Runtime PM code resumes > the parent before the child, the resume operation will fail because > there is no dev_pm_ops for the shared parent. Not if the parent is disabled for runtime PM, which it is in this case, right? > So I wonder which way that is the best to allow resuming platform > devices. Patch [02/05] is one way, but maybe there are more elegant > ways to handle it? Should the platform code be modified instead? If > so, how? I suppose root hubs for USB may have a similar issue, no? If necessary, I would suggest adding appropriate dummy runtime PM routines for that catch-all parent device. But it may not be necessary. > >> [PATCH 03/05] PM: Runtime PM v13 - add debug printouts > > > > This looks good. > > Thanks. Maybe it's a good plan to add similar printouts to other > functions as well? Perhaps so. When writing similar code for USB I found that lots of debugging printouts were needed all over the place, to get everything working right. Once it was working, they were a nuisance. Alan Stern _______________________________________________ linux-pm mailing list linux-pm@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linux-foundation.org/mailman/listinfo/linux-pm
