Subject: Re: device tree traversal
To: Jachym Holecek <>
From: Matthias Drochner <>
List: tech-kern
Date: 07/03/2006 14:20:36 said:
>  This will be needed for proper powerhooks

In the PCI case, I don't think traversing the (logical)
device list is the right thing to to. What we need is
to traverse the physical list. And this can only be done
by the bus drivers theirselfes.

Some reasons:
-On a shared bus, all devices need to support a certain
 low-power state before the bus can be stopped, powered
 down or so. _All_ devices, not just these we have drivers
 attached for. The bus driver might also find out a
 common denominator at the beginning and handle individual
 devices later.
-In PCI PM, most things can be done centrally. All the
 wakeup stuff and config register saving which is now
 in powerhooks shouldn't be there. So a call to the PCI
 device driver should be only done if the driver requests
 this. (There is a bit in the PCI PM capability which tells
 whether special driver assistance is needed. If this is
 set and the driver didn't register a hook, this would be
 an error.
-The namespace for PCI device power states  is different
 from the PCI bus one, and that of ACPI. For sanity, I
 wouldn't try to hide this behind global names. The bus driver
 can well translate bus power states into device power
 states. (And as said, this is not just translation but
 rather negotiation.)

best regards