Runtime PM for SCSI
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From: Alan Stern on 18 Feb 2010 16:00 Developers have been receiving complaints about Linux's inability to power-down card readers when they're not in use. To address this issue properly requires implementing runtime PM in the SCSI layer. (For a discussion of the current Runtime PM framework, see Documentation/power/runtime_pm.txt.) To begin with, it seems best to be safe: Don't suspend devices unless the device file is closed and there are no dirty buffers. This last requirement arises because lots of USB card readers give spurious "Media may have changed" codes when resumed; if they had dirty buffers when suspended then the information would be lost. Hence my first question: Can somebody tell me how to determine whether a block device has any dirty buffers? (And is there a particularly good place in the SCSI layer or the block layer to test whether the last dirty buffer has just been written out, or must this test be made whenever a command completes?) My second question: What are all the paths by which a command may be added to the queue of a SCSI device whose file isn't open? The possibilities I'm aware of include: the sg driver (whose device file must itself be open); dirty-buffer writeback; the error handler thread; scsi_reset_provider(). Are there any others? Alan Stern -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo(a)vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/ |