lkml.org 
[lkml]   [2008]   [Aug]   [25]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    From
    SubjectRe: [linux-pm] Power management for SCSI
    Date
    Am Dienstag 19 August 2008 17:28:28 schrieb Alan Stern:
    > On Tue, 19 Aug 2008, Oliver Neukum wrote:

    > > I suggest by talking to the HLDs.
    >
    > Why would the HLD (= ULD?) know?
    >
    > For example, consider a USB disk drive. How is sd.c (the HLD) supposed
    > to know that it's not safe to suspend the USB link without spinning
    > down the drive? Or consider a traditional SCSI parallel interface

    The HLD is responsible for suspending the disk in case the system is
    suspended. The HLD must know how to safely suspend a device. It may be
    overcautious, but it'll work.

    > > It seems to me that abstractly talking there are three criteria for suspension
    > >
    > > - the cpu needs to talk to the device now
    >
    > I.e., whether the idle timeout has expired, right?
    >
    > > - the device may need to talk to the CPU at unpredictable times
    >
    > I.e, whether remote wakeup needs to be enabled, right?

    I am talking about correctness for controllers. So remote wakeup may or may not
    be available. Likewise the bus may be able to predict how long it'll be idle.

    > > - suspending has side effects
    >
    > I'm not sure what you mean by that. Suspension always has side effects
    > of one kind or another.

    But not outside the controller. If you suspend the root hub of a usb bus,
    you suspend everything on the bus. It's a feature of the hardware. Other
    busses are different.


    > There's nothing about my suspend framework to prevent a driver from
    > autosuspending its device while the children are still active.
    > Rather, the framework insists on notifications going the other way:
    > The driver has to be told whenever one of its device's children is
    > suspended or resumed.

    That's the problem. You don't tell the children when the parent might want
    to suspend.

    Regards
    Oliver


    \
     
     \ /
      Last update: 2008-08-25 14:51    [W:2.392 / U:0.116 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site