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Subject: Re: [virtio-dev] Re: [PATCH v3 3/4] content: Introduce driver/device auxiliary notifications for MMIO
On Mon, Oct 31, 2022 at 01:24:30PM -0400, Stefan Hajnoczi wrote: > On Mon, Oct 31, 2022 at 11:45:55AM -0400, Michael S. Tsirkin wrote: > > On Thu, Oct 27, 2022 at 05:27:28PM -0400, Stefan Hajnoczi wrote: > > > On Fri, Oct 07, 2022 at 05:56:42PM +0100, Usama Arif wrote: > > > > This includes the additions to the corresponding device and driver > > > > conformances. > > > > > > > > Signed-off-by: Usama Arif <usama.arif@bytedance.com> > > > > Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com> > > > > > > You can keep this. One thought: > > > > > > I realized that virtio-mmio support won't be very useful until > > > virtio-mmio gets MSI-X support because drivers currently cannot > > > differentiate between device auxiliary notifications. > > > > > > Stefan > > > > > > The big issue with MSI is it actually needs a ton of registers > > for interrupt rebalancing, masking etc and they need to be fast. > > Maybe a status bit like pci has makes sense here. > > This patch does add an ISR bit: > > diff --git a/content.tex b/content.tex > index 33362b7..8968fcd 100644 > --- a/content.tex > +++ b/content.tex > @@ -2049,6 +2049,8 @@ \subsection{MMIO Device Register Layout}\label{sec:Virtio Transport Options / Vi > in at least one of the active virtual queues. > \item [Configuration Change Notification] - bit 1 - the interrupt was > asserted because the configuration of the device has changed. > + \item [Device-specific Driver Auxiliary Notification] - bit 2 - the interrupt was > + asserted because a device-specific event occurred to notify the driver. > > The problem is that the driver doesn't know which device-specific event > occurred, so the mechanism is less useful than the MSI-X approach where > the driver knows exactly which (of potentially many) device-specific > events occurred. > > Stefan Right I figured that out after sending this. So it's limited to one event type.
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