cvs commit: src/sys/dev/pci pci.c

[Nate Lawson]

On Sat, 22 May 2004, M. Warner Losh wrote:
> In message: <20040522103658.P58631 at root.org>
>             Nate Lawson <nate at root.org> writes:
> : On Fri, 21 May 2004, M. Warner Losh wrote:
> : > In message: <40ADAF07.2070909 at freebsd.org>
> : >             Scott Long <scottl at freebsd.org> writes:
> : > : Warner Losh wrote:
> : > : >   MFp4: o save/restore subvendor, subdevice, vendor, device, baseclass,
> : > : >           subclass, progif and revid.  While these are typically read
> : > : >           only fields, they aren't always read-only.  progif is writable
> : > : >           for ata devices, for example.  It does no harm when they are
> : > : >           read only, and helps when they aren't.
> : > : >
> : > : >   Revision  Changes    Path
> : > : >   1.252     +16 -0     src/sys/dev/pci/pci.c
> : > :
> : > : Shouldn't it be left up to the device drivers to decide if a buggy piece
> : > : of silicon needs to be touched like this?  I really don't like the bus
> : > : unilaterally enforcing this on everything.
> : >
> : > This just preserves the values across a D3 -> D0 state transition.
> : > This seems to be required by the 1.1 version of the pci power spec:
> : >
> : > 	Section 5.4: "When a function is brought back to D0...,
> : > 	software will need to perform a full initialization of the
> : > 	function, including its PCI Configuration space."
> : >
> : > 	Section 8.3.3: For example, reinitialization includes, but is
> : > 	not necessarily limited to, restoring the Base Address
> : > 	registers, re-enabling the I/O and memory spaces, re-enabling
> : > 	bus master capabilities, and unmasking any IRQs or PCI
> : > 	Interrupts as well as restoring the INT Line
> : > 	register. Furthermore, if the function has the DSI bit set,
> : > 	the operating system is required to execute whatever
> : > 	initialization code is necessary, either via the device
> : > 	driver's initialization code or by executing POST.
> : >
> : > My reading of these two sections lead me to save this information.
> :
> : I didn't know the code didn't do this fully before.  Yes, it is important
> : to save/restore all the headers across a D3 transition.  I don't know of
> : any devices this breaks.
>
> Well, we're talking exclusively about the vendor, device, subvendor,
> subdevice, class, subclass and progif fields, which are obstensively
> read-only.  However, the pci standards are self-contradictory.  The
> main 2.2 one says they are read-only (without defining what that means
> that I could find), yet the pciide spec says that progif had writable
> bits...

I think the progif is the only one of that list that you need to restore,
as per your reading of the specs.  Since the others are identifiers, they
probably don't need to be restored.

-Nate