In the grand open source tradition of "pass the buck", I've long been
hoping that someone would take a few days, sit down, and hammer out the
policy side of this.
We -don't- want to do hotplug-active all the time -- the current default
in all drivers that support device hotplug -- because it needlessly
keeps parts active that are unused 99.9% of the time [when they are empty].
Admins need a generic way to control SATA ports and links from
userspace. Within that, admins need to be able to set a link's hotplug
state among three choices: hotplug-active [when supported],
hotplug-poll, and hotplug-never. And of course, hotplug-poll's interval
should be tunable.
And of course this control interface needs to be usable on SAS/SATA
cards that will be common in the future (broadsas, mvsas are early
examples).
This is why I look askance at an AHCI BIOS flag. That's merely a hint,
and potentially unreliable one at that. It could just be describing
what the BIOS writer felt were the ports that _should_ be hotpluggable
-- i.e. not even describing what is _possible_ but someone's definition
of "reasonable." The BIOS flag might even be filled with fuzz (AHCI's
BIOS-written registers have occasionally been shipped into the field
uninitialized).
A better solution involves taking the BIOS flag and using that to set a
default policy that an admin can easily override using the
above-mentioned control interface.
Because in some cases, that BIOS flag might do the wrong thing, and we
need to give the admin an ability to undo the damage.
Jeff
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