Date: Thu, 5 Dec 2013 22:43:56 -0700 From: Warner Losh <imp@bsdimp.com> To: Eitan Adler <lists@eitanadler.com> Cc: "freebsd-arch@freebsd.org" <arch@freebsd.org> Subject: Re: hw.pci.do_power_nodriver=3 Message-ID: <E24C9357-B0A8-48D1-8D80-DAC5B09580EF@bsdimp.com> In-Reply-To: <CAF6rxgmeBAa9LK%2BHWU7NKUkW6RZvk_dNGDpN%2BJ43L=BdUsqHwQ@mail.gmail.com> References: <CAF6rxg=cSkTGLFZCeeg6C0V=frQN1iYtpLZBrNAu4WAQCX63Lw@mail.gmail.com> <CAF6rxgmeBAa9LK%2BHWU7NKUkW6RZvk_dNGDpN%2BJ43L=BdUsqHwQ@mail.gmail.com>
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On Dec 5, 2013, at 9:12 PM, Eitan Adler wrote:
> Is there any reason we can not set hw.pci.do_power_nodriver=3D3 by =
default?
>=20
> My understanding is that there were problems with hardware being
> powered off and not being powered back on when drivers were loaded.
> Is this still a concern? If yes, can we flip the switch in HEAD and
> fix the drivers?
The reason it was for Adaptec RAID controllers.
They had a weird topology:
<-------------------- aac based card =
-------------------------->
pci bus ---- pci bridge ---- pci bus ---+----- some chip with =
driver
=
+----- chip without driver
so, when the enumeration code saw that there was no driver attached to =
the second chip, it would power it down. Turns out, this chip, while it =
didn't have a driver, was critical to the proper functioning of the RAID =
card. Scott Long turned off the default power saving because he was =
worried there were other parts like this. In addition, in an abundance =
of caution, he also created stub drivers for the second chip for each of =
the then known aac cards.
Since then, it is unknown if others have followed this design or not, so =
it is unknown our exposure if we were to flip this to have a different =
default.
Warner
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