Re: [Qemu-devel] Re: questions on default_config_write in hw/pci.c

["M. Warner Losh" <imp@bsdimp.com>]

In message: <20090430171526.GA10638@amt.cnet>
            Marcelo Tosatti <mtosatti@redhat.com> writes:
: On Thu, Apr 30, 2009 at 07:15:08PM +0300, Michael S. Tsirkin wrote:
: > Hi,
: > I've been looking at hw/pci.c, specifically at how config
: > read/write are implemented, and have a couple of questions
: > about default_config_write:
: > 
: > 1. The code at the beginning (if len == 4 ...)
: >    seems to only update pci base registers if a dword write 
: >    is performed. I think it's legal for the guest to perform 4
: >    single-byte writes. Should this be supported?
: > 
: > 2. The large switch statement at the end of this function
: >    uses hard-coded register offsets. Would it make sense
: >    to change it to use macros from hw/pci.h?
: > 
: > 3. Still there I see:
: >         switch(d->config[0x0e]) {
: >         case 0x00:
: >         case 0x80:
: >    register 0x0e is header type, which has defined values
: >    of 0x00 (device or host bridge), 0x01 (pci to pci bridge) and
: >    0x02 (cardbus bridge). What is 0x80 and when is it used?
: >    Would it make sense to remove this?
: 
: Don't know. Check the PCI spec?

The above is a bug.  0x80 is a bit that says "I have multiple
functions" and is orthogonal to the type of device.  

: >         switch(d->config[0x0e]) {

should be

	switch(d->config[0x0e] & 0x7f) {

: > 4. Still there, there's some handling done for type 1 devices.
: >    This support seems imcomplete.
: >    Are there any PCI-to-PCI bridges emulated by qemu?
: >    Would it make sense to remove this code?
: 
: 
: It did work at one point:
: 
: http://www.mail-archive.com/kvm-devel@lists.sourceforge.net/msg16647.html

I have vague plans to do Cardbus-to-PCI bridge at some point...

Warner