On Tue, 28 Dec 2010, Ohad Ben-Cohen wrote: > On Sun, Dec 26, 2010 at 7:00 PM, Alan Stern <stern@xxxxxxxxxxxxxxxxxxx> wrote: > > Hmm. It's a little difficult to untangle the web of dev_pm_ops > > pointers and other stuff. > > Yeah, SDIO suspend/resume is very different from other subsystems. > > There are several layers of abstractions involved, from the host > controller driver, to the MMC core code, to the SDIO core code, to > finally get to the actual SDIO function driver. Actually that sounds quite a lot like the USB subsystem, except perhaps for the fact that you have two layers of core code instead of just one. The cards are much like USB devices (indivisible for the purposes of power management) and the functions are much like USB interfaces (bound to individual drivers but not independently power-managed or resettable). > I'll try to explain it below by addressing your questions. If > something is still unclear, feel free to ask me. > > > There's wl1271_suspend() and wl1271_resume() > > (which don't do anything) > > It just looks like they don't. In fact, by returning 0, > wl1271_suspend() is telling the SDIO subsystem that it's OK to power > down the SDIO function (in general an SDIO card can have several SDIO > functions, each of which may be driven by a separate SDIO driver). If > all the SDIO functions agreed, then SDIO core (mmc_sdio_suspend()) > tells MMC core (mmc_suspend_host()) it's OK to power down the card (by > directly calling mmc_power_off()). What's the relation between mmc_power_off() and mmc_power_save_host()? When you say "power down", which of these routines do you mean? I get the feeling that sometimes you mean one and sometimes the other, which leads to problems in understanding. Why are there two separate routines? Does one merely go into a low-power state whereas the other does the complete-power-off reset? If so, which does which? What's the reason for not going into the complete-power-off state every time? If it is latency, shouldn't the runtime-PM path use the low-latency routine and the system-sleep path use the high-latency routine? Although I can't tell for certain, it seems to be the other way around. > > Under what circumstances does the MMC/SDIO core call > > wl1271_sdio_set_power(), and where are those function calls? > > The relations are actually reversed: the MMC/SDIO core never calls > this function. > > This function is called by the wl1271 driver itself, mostly as a > response to a request by the mac80211 layer (but also as a response to > a hardware error), that requires manipulation of the power of the > card. > > There are a handful of reasons this may happen: > > error recovery: > > wl1271_recovery_work() -> > __wl1271_op_remove_interface() -> > wl1271_power_off() -> > wl1271_sdio_set_power() -> > wl1271_sdio_power_off() -> > pm_runtime_put_sync() > > wlan interface goes down: > > ieee80211_do_stop() -> > wl1271_op_remove_interface() -> > __wl1271_op_remove_interface() -> > ... > > system suspend: > > __ieee80211_suspend -> > wl1271_op_remove_interface() -> > ... Okay. These paths should be interrelated with power management in a different way. It's correct for wl1271_op_remove_interface() to be called in these three situations, and it's correct to do a pm_runtime_put_sync(). But it's not correct to rely on that to actually change any power levels or do a reset. Instead, wl1271_error_recovery_work() should call either mmc_suspend_host() or mmc_power_save_host() (whichever one does the actual power-off reset) directly, after calling wl1271_power_off(). In fact, you might even want to do a pm_runtime_get_noresume() before calling wl1271_power_off(), to prevent the PM core from interfering with the reset. Similarly, during system suspend mmc_suspend_host() should be responsible for doing all the necessary power-down operations. Runtime PM is completely out of the picture at this time. And this should be independent of mac80211 -- in fact, the card should be powered down appropriately even if the kernel doesn't have a mac80211 layer. During wlan-interface-down, it's not necessary to reduce the power level; it's merely desirable. That's exactly the sort of thing runtime PM is meant for. Hence the existing call to pm_runtime_put_sync() is sufficient. > > Is it possible for there to be more than one device connected to the > > same MMC/SDIO controller? > > Generally yes, host controllers may have several slots, but to the > MMC/SDIO core, it is presented as each slot is a separate host > controller (personally I have never seen such hardware, but I did find > an example for that in the host controller's source folder). Put it another way: Suppose an SDIO card has more than one function and you need to reset the wl1271 function. It sounds like there's no way to do this without resetting the other functions as well. What happens if another function's driver is busy and can't allow a reset just then? Alan Stern -- To unsubscribe from this list: send the line "unsubscribe linux-mmc" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
