virtio — archive

[PATCH] pci: missing documentation for dealing with 64 bit config fields

From: Michael S. Tsirkin <[email protected]>
To: [email protected]
Date: Thu, 02 Apr 2015 10:07:00 -0000

On Thu, Apr 02, 2015 at 11:01:45AM +0200, Cornelia Huck wrote: > On Wed, 1 Apr 2015 20:42:13 +0200 > "Michael S. Tsirkin" <[email protected]> wrote: > > > pci spec says what width access to use for 32, 16 and 8 > > bit fields, but does not explicitly say what to do for > > 32 bit fields. As we have text that says driver must > > s/32/64/ > > > treat 64 bit accesses as non-atomic, this seems > > to imply driver should always do two 32 bit wide accesses. > > > > Let's make this an explicit requirement, and require > > devices to support this. > > > > VIRTIO-139 > > > > Signed-off-by: Michael S. Tsirkin <[email protected]> > > --- > > conformance.tex | 1 + > > content.tex | 19 ++++++++++++++ ----- > > 2 files changed, 15 insertions(+), 5 deletions(-) > > (...) > > > +For device configuration access, the driver MUST use 8-bit wide > > +accesses for 8-bit wide fields, 16-bit wide and aligned accesses > > +for 16-bit wide fields and 32-bit wide and aligned accesses for > > +32-bit and 64-bit wide fields. For 64-bit fields, the driver MAY > > +access each of the high and low 32-bit parts of the field > > +independently. > > Doesn't the last sentence follow from "use 32-bit wide accesses" > already? Someone might assume that driver must always access low part, then high part. Last sentence says it does not have to. -- MST