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

[Nate Lawson]

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:
> : > imp         2004/05/20 23:36:36 PDT
> : >
> : >   FreeBSD src repository
> : >
> : >   Modified files:
> : >     sys/dev/pci          pci.c
> : >   Log:
> : >   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.

-Nate