On Thursday 13 September 2012 10:26:44 James Bottomley wrote: > On Thu, 2012-09-13 at 17:07 +0800, Aaron Lu wrote: > > So I think this is basically 2 things, one is the runtime suspend of the > > disk, another is when it is runtime suspended, how to remove its power. > > I'm currently doing the latter one, which is simpler, so I want to do it > > first :-) > > Well, I don't like the way the interaction of the patches is going. > You're the one proposing powering down the device outside of the > standards defined transitions, so you need to be responsible for the > actions that necessitates, including synchronizing the cache. The specs > (SPC-4) say that cache management is explicitly unnecessary for the > standard SCSI power states (Active, Idle, Standby and Stopped), so > someone at some point is going to read that and remove the unnecessary > cache sync in the code. When that happens, you'll start getting data > loss. The cache is handled identically in sd_suspend() and sd_shutdown(). In fact sd_shutdown() will skip handling it if the device has already been suspended, so the assumption is built into the code and has been so for a long time. Though it wouldn't hurt to add a comment that says that the system going to S3 or S4 will cut power to a lot of disk so that the cache needs to be synced even if the spec says we need not. Runtime PM doesn't much alter the situation. Regards Oliver -- To unsubscribe from this list: send the line "unsubscribe linux-scsi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
