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? Kevin -- 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
