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Re: [ CVS commit: src/sys/kern]

On Fri, Feb 22, 2008 at 03:58:02PM +0100, Joerg Sonnenberger wrote:
> Please back this changes out until the discussion of how to handle
> (a) the console
> (b) shutdown of devices
> has been fully discussed.
> Your change are bad in two different ways:
> (1) It reintroduces the behaviour of letting devices active, leading to
> possible corruption of system memory after reboot e.g. due to bus master
> DMA. This is the same class as firmwares that have issues with
> activating devices from D3. Contrary to your claims D3 is not used on
> shutdown/reboot.
> (2) The changes for wd/sd once again make it impossible to correctly
> order dependencies. You don't want to spin down the disk before all
> consumers are processed. Consider RAID.
> The correct handling of console devices has to consider power management
> and whether or not the device used is currently active. It also has be
> extended to allow e.g. reset of the VGA console when the system is
> currently under X11 in case of entering DDB. The pckbd driver had a bug
> that it assumed that the keyboard is active, which is fixed. The
> assumption that the ISA bridge is working at that point is very weak for
> the reboot case.
> The two step approach for handling other devices remains:
> (1) If the device has a detach function and no remaining children, call it.
> (2) If the device supports suspend, call it.
> The former adresses modern devcies and should be the default. The detach
> pathshould restore the device to a sane state, but most importantly make
> sure that the device itself is quiet. This is very similiar to the
> requirements of suspend. The latter tries to deal with devices that have
> unsupported children. Hopefully it can go away soon enough.


How do you propose to handle the console?  Please be more explicit.
It seems that step (1) potentially detaches the console, which may stop
it from working, and (2) potentially suspends the console, which we know
has stopped it from working.


David Young             OJC Technologies      Urbana, IL * (217) 278-3933 ext 24

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