On 27/05/16 12:46, Krzysztof Kozlowski wrote: > On 05/27/2016 12:28 PM, Jon Hunter wrote: >> Hi Krzysztof, >> >> On 27/05/16 09:37, Krzysztof Kozlowski wrote: >> >> ... >> >>> Indeed I was struggling with similar issue in bq27x00_battery. The issue >>> was introduced by... me :( when moving the ownership of power supply >>> structure from driver to the core. However IMHO my change exposed the >>> fundamental problem with power supply. >>> >>> Anyway a fix for this issue was: >>> 7f1a57fdd6cb6e7b (power_supply: Fix possible NULL pointer dereference on >>> early uevent) >>> AFAIU, this fix no longer fixes all the issues, right? >>> >>> As for the fundamental problem, the power supply core should not call >>> back the driver (get_property()) until the probe ends. Even if the >>> di->bat was initialized, some other fields of driver could not be set >>> yet. In general, the probe did not end so we should avoid calling driver >>> internal functions. >> >> For my understanding, can you elaborate why the power-supply core should >> not call back to the drivers ->get_property() before the probe ends? I >> assume that registering the power-supply should be the last thing done >> in the probe and so the power-supply should be configured at that point. > > It is not only about power supply but other resources allocated by the > driver. If the power_supply_register() is a last call, then no problem. > But if not, then these resources won't be available. > > Actually I exaggerated a little bit as a fundamental problem as this is > quite common pattern. When driver provides something (like power supply) > then after registration it should be ready for calls coming from the > core or user space. It does not have to be power supply. It might be > exposing sysfs entries or file operations (exposed before calling > power_supply_register()). Right, exactly when you register with the power-supply core the device better be ready so that handle any incoming calls. >> The problems with the bq27xxx seem to stem from the periodic update of >> the bq27xxx status and so it is not clear to me that this is a generic >> problem for all power-supply devices. > > Initially, the generic problem was that the core would call back the > driver from power_supply_register() in a synchronous way through > power_supply_changed(). The commit 7f1a57fdd6c changed it to an > asynchronous call. Here it looks like the same problem - the > power_supply_register() calls thermal which calls > thermal_zone_device_update() and we are back at the driver... before > finishing power_supply_register() call. So I am still not convinced this is a generic problem but a problem with the bq27xxx. In fact, I think that commit 7f1a57fdd6c could be avoided if we did something like ... http://marc.info/?l=linux-kernel&m=146425896332433&w=2 AFAICT in most cases, in ->get_property() you should have no need to access a driver's equivalent of di->bat, because you have already been passed a pointer to this via the *psy argument. Cheers Jon -- nvpublic -- To unsubscribe from this list: send the line "unsubscribe linux-tegra" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
