2013/3/7 Kevin Liu <keyuan.liu@xxxxxxxxx>: > 2013/3/7 Ulf Hansson <ulf.hansson@xxxxxxxxxx>: >> On 7 March 2013 01:12, Kevin Liu <keyuan.liu@xxxxxxxxx> wrote: >>>> From: Ulf Hansson <ulf.hansson@xxxxxxxxxxxxxx<mailto:ulf.hansson@xxxxxxxxxxxxxx>> >>>> Date: Fri, Mar 1, 2013 at 8:47 PM >>>> Subject: [PATCH 0/3] mmc: Use runtime pm for blkdevice >>>> To: linux-mmc@xxxxxxxxxxxxxxx<mailto:linux-mmc@xxxxxxxxxxxxxxx>, Chris Ball <cjb@xxxxxxxxxx<mailto:cjb@xxxxxxxxxx>> >>>> Cc: Johan Rudholm <johan.rudholm@xxxxxxxxxxxxxx<mailto:johan.rudholm@xxxxxxxxxxxxxx>>, Ulf Hansson <ulf.hansson@xxxxxxxxxx<mailto:ulf.hansson@xxxxxxxxxx>> >>>> >>>> >>>> From: Ulf Hansson <ulf.hansson@xxxxxxxxxx<mailto:ulf.hansson@xxxxxxxxxx>> >>>> >>>> SDIO has been using runtime pm for a while to handle runtime power save >>>> operations. This patchset is enabling the option to make the sd/mmc >>>> blockdevices to use runtime pm as well. >>>> >>>> The runtime pm implementation for the block device will make use of >>>> autosuspend to defer power save operation to after request inactivty for >>>> a certain time. >>>> >>>> To actually perform some power save operations the corresponding bus ops >>>> for mmc and sd shall be implemented. Typically it could make sense to do >>>> BKOPS for eMMC in here. >>>> >>>> Ulf Hansson (3): >>>> mmc: core: Remove power_restore bus_ops for mmc and sd >>>> mmc: core: Add bus_ops for runtime pm callbacks >>>> mmc: block: Enable runtime pm for mmc blkdevice >>>> >>> Ulf, >>> >>> sdhci.c has added pm_runtime which also protect between request and >>> task finish. And some sdhci.c based host drivers has provided >>> pm_runtime_suspend/resume functions like sdhci-pxav3.c. From the >>> powersave viewpoint, I think adding pm_runtime in driver level is >>> better than doing that on bus level since the control granularity is >>> even smaller. And adding pm_runtime in both block.c and sdhci.c will >>> call pm_runtime twice. How do you think? >>> >>> Thanks >>> Kevin >> >> Hi Kevin, >> >> Thanks for your response! >> >> It seems like we need some more clarification around this area. >> Runtime pm for a host device driver shall ultimately be responsible >> for taking care of runtime power management of the host device - only. >> It should not handle runtime power management of a block device, which >> in principle means BKOPS shall be handled in the blkdevice. At least >> this is my view. >> >> So, why is this? I will try to elaborate on the runtime pm support in >> host drivers here. >> The host device driver controls a MMC/SD/SDIO IP. This IP could very >> well reside (for some SoC) in what you call a power domain. In >> principle, once the IP needs to be used, a host driver has done a >> pm_runtime_get of it's device. This will mean a reference to the power >> domain has been fetched. Once the IP is not needed any more, >> pm_runtime_put is done and the reference to the power domain is >> released. Once no reference to the power domain exist the power domain >> can enter lower sleep states, which is preferred to happen as soon as >> possible and as long as possible - of course. >> >> Hope this gives a better understanding. :-) >> > Ulf, > > Thanks for the explanations! > Then do you mean to start bkops when blkdev pm_runtime auto suspended > while stop bkops when blkdev pm_runtime resumed? > My only concern is that we have implemented pm_runtime for host device > and its pm_runtime functions will turn on/off bus clock when host dev > runtime resume/suspend. Let's see below sequence when an issue request > come: > 1. blkdev pm_runtime resumed in mmc_blk_issue_rq. > 2. blkdev issue request > 3. host dev pm_runtime resumed in host->ops->request. > 4. host finished the transfer and host dev pm_runtime suspended. > 5. 3s later, blkdev pm_runtime suspended. > The bus clock will be turn off in step 4 by host dev > pm_runtime_suspend function. Then how can bkops run in step 5? > My question is host dev will stop bus clock by pm_runtime_suspend once the request transfer is finished. But bkops on emmc chip should still need the bus clock after bkops started. How to handle this? -- 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
