Re: [virtio] [PATCH] virtio-pci: access device using config

["Michael S. Tsirkin" <mst@redhat.com>]

On Tue, Nov 05, 2013 at 04:57:29PM +1030, Rusty Russell wrote:
> "Michael S. Tsirkin" <mst@redhat.com> writes:
> > VIRTIO-39.
> 
> We can discuss this on the call, but I don't like this.
> 
> PXE boot style environments will have to handle memory bars for modern
> PCIE devices.  Why should virtio be special?
> 
> Cheers,
> Rusty.

Didn't we discuss this requirement many times already?
AFAIK e.g. disk interrupt handler is problematic like this too.
So all disks must have a way to access them with config.

CC hpa who confirmed this is a hard requirement, in the past.
Cc gleb who wrote virtio blk bios drivers.

> > Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
> > ---
> >  virtio-v1.0-wd01-part1-specification.txt | 26 ++++++++++++++++++++++++++
> >  1 file changed, 26 insertions(+)
> >
> > diff --git a/virtio-v1.0-wd01-part1-specification.txt b/virtio-v1.0-wd01-part1-specification.txt
> > index ce79c05..d71c021 100644
> > --- a/virtio-v1.0-wd01-part1-specification.txt
> > +++ b/virtio-v1.0-wd01-part1-specification.txt
> > @@ -1038,6 +1038,8 @@ cfg_type
> >  	#define VIRTIO_PCI_CAP_ISR_CFG		3
> >  	/* Device specific configuration */
> >  	#define VIRTIO_PCI_CAP_DEVICE_CFG	4
> > +	/* PCI configuration access */
> > +	#define VIRTIO_PCI_CAP_PCI_CFG		5
> >  
> >  	Any other value - reserved for future use. Drivers must
> >  	ignore any vendor-specific capability structure which has
> > @@ -1101,6 +1103,30 @@ notify_off_multiplier
> >  	If notify_off_multiplier is 0, all virtqueues use the same address in
> >  	the Notifications structure!
> >  
> > +If cfg_type is VIRTIO_PCI_CAP_PCI_CFG the fields bar, offset and length are RW
> > +and this structure is immediately followed by an additional field:
> > +
> > +struct virtio_pci_cfg_cap {
> > +	__u8 pci_cfg_data[4];	/* Data for BAR access. */
> > +};
> > +
> > +pci_cfg_data
> > +
> > +	This RW field allows an indirect access to any BAR on the
> > +	device using PCI configuration accesses.
> > +
> > +	The BAR to access is selected using the bar field.
> > +	The length of the access is specified by the length
> > +	field, which can be set to 1, 2 and 4.
> > +	The offset within the BAR is specified by the offset
> > +	field, which must be aligned to length bytes.
> > +
> > +	After this field is written by driver, the first length
> > +	bytes in pci_cfg_data are written at the selected
> > +	offset in the selected BAR.
> > +
> > +	When this field is read by driver, length bytes at the
> > +	selected offset in the selected BAR are read into pci_cfg_data.
> >  
> >  100.100.1.3.1.1. Legacy Interface: A Note on Device Layout Detection
> >  -------------------------------
> > -- 
> > MST
> >
> > ---------------------------------------------------------------------
> > To unsubscribe from this mail list, you must leave the OASIS TC that 
> > generates this mail.  Follow this link to all your TCs in OASIS at:
> > https://www.oasis-open.org/apps/org/workgroup/portal/my_workgroups.php