Re: [gentoo-user] AHCI/IDE-question

Mark Knecht <markknecht@×××××.com> [11-01-21 20:16]:
> On Fri, Jan 21, 2011 at 10:45 AM,  <meino.cramer@×××.de> wrote:
> >
> > Hi,
> >
> > I got a little confused about the sense or nonsense of AHCI vs. IDE.
> >
> > I run a ASUS Crosshair IV Formula, which BIOS has a menu entry to
> > configure the SATA ports either for IDE or AHCI or RAID. Forget RAID
> > for a momen -- I dont use it (nothing against RAID ! ;)
> >
> > My box uses a linux 2.6.37 vanilla kernel.
> >
> > The kernel config has been set to
> >
> >    CONFIG_SATA_AHCI=y
> >    # CONFIG_SATA_AHCI_PLATFORM is not set
> >
> > In the dmesg output I found this:
> >
> >    pci 0000:00:11.0: set SATA to AHCI mode
> >    ahci 0000:00:11.0: AHCI 0001.0200 32 slots 4 ports 3 Gbps 0xf impl SATA mode
> >    ahci 0000:07:00.0: AHCI 0001.0000 32 slots 2 ports 3 Gbps 0x3 impl SATA mode
> >
> > despite the fact that AHCI is disabled in the BIOS settings (using
> > IDE).
> >
> > I did an experiment an disabled AHCI in the kernel (to make the kernel
> > settings consistent with the BIOS.)
> >
> > Result: The kernel did not find the root partition.
> >
> > In the meanwhile I do not understand all this never more.
> >
> > Why does the kernel boots only, if the BIOS says "IDE!" and linux
> > insists on "AHCI!"...and waht ist the result?
> >
> > Best regards,
> > mcc
>
> Hi meino,
>    It's disappointing that Volker insists on sending these pissy
> little responses which don't advance the conversation. Sorry for that.
>
>    Not sure I can lend any weight to the argument but it's my belief
> that your installation of Gentoo Linux isn't using BIOS to access the
> disk at all. Once the system boots and loads the kernel, then the
> kernel loads drivers (or uses what you built into the kernel) and
> takes over control of the hardware using the AHCI drivers. If the
> kernel doesn't use BIOS disk calls (INT13?) then it doesn't care what
> the BIOS thinks because the BIOS is not longer involved. It just talks
> directly to the hardware.
>
>    I'm happy to be corrected (by Volker I'm sure) but that's my guess
> as to what you're seeing.
>
>    Good luck!
>
> Cheers,
> Mark
>

Hi Mark,

thank you for your kind words. There is no need to feel sorry for
others. The behaviour of those are definelty neither your fault nor
your problem ;)

For me I have learned that it doesn't matter, whether the result
of an experiment is positive or negative as long as one is prepared
to learn from it. If one insisits on doing only so called "non stupid
things" one will miss a lot of results sooner or later... ;) ;)

I thought (which implies "I dont know for sure"), that the BIOS do
enable/disable certain features, the kernels reads that settings and
act accordingly -- but definitely this is not true for all settings.

Does the contents of a harddisk differ when written with AHCI
compared to a disk which is written with IDE?

If NO _AND_ only the kernel sets the AHCI- odr IDE-protocol, then
the harddisk should be readable in either case.

If the BIOS _and_ the kernel settings are defining, how to talk 
to the disk, then it may happen, that there is only the "sound of silence"
between kernel and hardware if before the BIOS set up the SATA-chips
differently to what the kernel wants to talk.

But again, these are only thougts drifting in the dark.

I tried to shed some more light (for getting greater shadows ;) )
by posting my question here... ;) 8)

May be I should do some more stupid things??? ;)

Thanks again for your help and your words, Mark!
Have a nice weekend!
Best regards,
mcc