Re: [PATCH RFC] ahci: implement handoff quirk

[Jeff Garzik <jeff@garzik.org>]

Tejun Heo wrote:
> Jeff Garzik wrote:
>> Tejun Heo wrote:
>>> Jeff Garzik wrote:
>>>> We probably need to do this...
>>>>
>>>> it's not a controller requirement but a BIOS one, so in theory even an
>>>> existing, deployed AHCI 1.2 platform could suddenly require BIOS/OS
>>>> handoff, if a BIOS update suddenly starts doing new and weird stuff
>>>> in SMI.
>>>>
>>>> Note that we need to do BIOS/OS handoff upon resume as well as at boot
>>>> time.
>>> Yeah, probably.  Do you know of any system which makes use of this
>>> feature?  I'm a bit uneasy about committing it without any testing.
>> I don't.
>>
>> But the purpose of the feature is to tell BIOS to cleanup and stop using
>> the hardware.  It's a dumb feature, because of compatibility realities,
>> but hey, other network and SCSI drivers have been doing this sort of
>> synchronization with their on-board firmwares for years.
>>
>> IMO the more dangerous route is to continue loading ahci, without first
>> telling the BIOS to clean up and get out of our way.
> 
> Hmmm.... yeah, I'm just worried a bit about adding a chunk of
> completely untested code.  How about adding a big fat warning message
> which gets triggered if the handoff thing seems to be active?

Yeah, printing out something makes a lot of sense, but I would just add 
it to the flags output in ahci_print_info() or similar.   If we don't 
see any further action from ahci (or the system as a whole), we know 
something exploded very early in the AHCI driver load.

Or maybe AMD (I see they're CC'd) could test this for us?  AMD, what say 
you?

	Jeff