On Fri, Sep 21, 2012 at 11:18:27PM +0200, Rafael J. Wysocki wrote: > On Friday, September 21, 2012, Aaron Lu wrote: > > On Thu, Sep 20, 2012 at 10:00:51PM +0200, Rafael J. Wysocki wrote: > > > On Wednesday, September 19, 2012, Aaron Lu wrote: > > > > Thanks Rafael, and if there is any question/problem, > > > > please kindly let me know. > > > > > > Well, unfortunately my initial review indicates that the patchset is not > > > quite ready to go upstream yet. > > > > > > I'll send comments in replies to the individual patches, but overall I can > > > say that at this stage of development, when I look at the patches, it should > > > be clear to me not only what is being changed, but _why_ it is being changed > > > in the first place and, secondly, why it is being changed in this particular > > > way. It's far from that, though. > > > > I'm adding zero power support for optical disk drive(ZPODD), which is > > made possible with the newly defined device attention(DA) pin introduced > > in SATA 3.1 spec. > > > > The idea here is to use runtime pm to achieve this, so I basically did 2 > > things: > > 1 Add runtime pm support for ODD; > > 2 Add power off support for ODD after it is runtime suspended. > > > > Patch 2 is runtime pm support for ODD, the reason it is done this way is > > discussed here: > > http://www.spinics.net/lists/linux-scsi/msg61551.html > > Why isn't it explained in the patch changelog, then? People should be able > to learn why things are done the way they are done from git logs. > > > The basic idea is, the ODD will be runtime suspended as long as there is > > nobody using it, that is, no programs opening the block device. > > > > The ODD will be polled periodically, so it will be runtime resumed > > before checking if there is any events pending and suspended when done. > > OK. So what happens if we power off the drive via runtime PM. Does it > it really make sense to resumie it through polling in that case? No, this is the reason I introduced the powered_off flag. If set, the poll will simply return without touching the device. I've tried to do a disk_block_events call on its suspend callback when it is ready to be powered off, but there is a race that I don't know how to solve: pm_runtime_suspend disk_events_workfn scsi_dev_type_suspend sr_block_check_events sr_suspend cdrom_check_events disk_block_events cdrom_update_events (this call waits for all sr_check_events running events_checking function scsi_autopm_get_device to return) Suppose sr_suspend runs first, and then sr_check_events comes in. sr_suspend calls disk_block_events, which waits for sr_check_events, while scsi_autopm_get_device wait for suspend callback to finish, deadlock. > > > The only exception is, if we found a disc is just inserted, we will not > > idle it immediately at the end of the poll, reason explained in another > > mail. > > > > This is the rational I wrote patch 2, and patch 1 is used by patch 2. > > > > Patch 3 is adding power off support for ODD after it is runtime > > suspended, the condition is specified in section 15: > > ftp://ftp.seagate.com/sff/INF-8090.PDF > > > > That is, for tray type ODD: no media inside and door closed; for slot > > type ODD: no media inside. > > > > The is the reason sr_suspend is written, for non-ZPODD capable devices, > > it does nothing; for ZPODD devices, it will check the above condition to > > see if it is ready to be powered off. The ready_to_power_off flag will be > > used by ATA layer to decide if power can be removed. > > Now, James says he doesn't like the way ready_to_power_off is used. Sure > enough, it is totally irrelevant to the majority of SCSI devices. It actually > is totally irrelevant to everything in the SCSI subsystem except for the sr > driver and libata. So I wonder if you have considered any alternative > way to address the use case at hand? > > > When in powered off state, if user presses the eject button or insert a > > disc, an ACPI event will be generated and our acpi wake handler will > > pm_runtime_resume the ODD. And if it is a tray type ODD, its tray should > > be ejected(need_eject flag) after powered on. This is patch 3. > > That sounds reasonable enough, but the role of the powered_off and > need_eject flags could be explained a bit better. In particular, it would powered_off: set when the device is powered off, clear otherwise. need_eject: First consider how the device will be runtime resumed: 1 Some program opens the block device; 2 Events checking poll when it's not powered off yet; 3 User presses the eject button or inserts a disc into the slot when the device is in powered off state. And the need_eject flag is for case 3, when the device is in powered off state and user presses the eject button, it will be powered on(through acpi wake notification function) and runtime resumed. In its runtime resume callback, its tray needs to be ejected since user just presses the eject button. The whole process of ZPODD is opaque to the user, he/she doesn't know the ODD lost power so the ODD has to behave exactly like it doesn't lose power. Hi Oliver, This flag is really to say the tray needs to be ejected after runtime resumed, it's not that media change detected. It is possible that user ejects the tray without putting any disc inside and simply close the tray, which doesn't qualify a media change event. And if user does put a disc in, the sr_check_events will find that and report the media change event to user space. Agree? > be nice to have explained why they have to be present in struct scsi_device, > because they don't seem to be particularly useful for many SCSI devices > that aren't CD drives (the need_eject one in particular). With your suggestion of pm_platform_power_off_allowed, I suppose powered_off can be eliminated similarly with something like pm_platform_powered_off returning true or false(for ACPI platform, return true when device is in D3 cold state). And for the need_eject flag, I don't know if there is a better place for it. The acpi wake notification code resides in libata(where we need to record that this resume is due to user presses the eject button and the tray needs to be ejected after resumed), and the runtime resume callback resides in scsi driver(where we actually eject the tray). Ideally, this flag should sit in scsi_cd structure, but libata does not have access to it. Thanks, Aaron > > > And patch 4-6 introduces a new sysfs file may_power_off to give user a > > chance to disable the power off of the device due to various reasons > > like the ODD claims support of device attention while actually it is > > broken. > > User space has an interface to disable runtime PM of any device and it looks > like that interface should be sufficient to disable the feature in question. > Why do you think the new interface is needed? > > > I hope it makes more sense to you now. > > Well, thanks for the explanation. :-) > > Rafael -- To unsubscribe from this list: send the line "unsubscribe linux-acpi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
