Re: [PATCH v2 5/6] drivers/hv/vmbus: Get the irq number from DeviceTree

[Roman Kisel]

On 5/17/2024 10:14 AM, Rob Herring wrote:
> On Tue, May 14, 2024 at 5:45 PM Roman Kisel <romank@xxxxxxxxxxxxxxxxxxx> wrote:
> > The vmbus driver uses ACPI for interrupt assignment on
> > arm64 hence it won't function in the VTL mode where only
> > DeviceTree can be used.
> >
> > Update the vmbus driver to discover interrupt configuration
> > via DeviceTree.
> >
> > Signed-off-by: Roman Kisel <romank@xxxxxxxxxxxxxxxxxxx>
> > ---
> >   drivers/hv/vmbus_drv.c | 37 +++++++++++++++++++++++++++++++++++++
> >   1 file changed, 37 insertions(+)
> >
> > diff --git a/drivers/hv/vmbus_drv.c b/drivers/hv/vmbus_drv.c
> > index e25223cee3ab..52f01bd1c947 100644
> > --- a/drivers/hv/vmbus_drv.c
> > +++ b/drivers/hv/vmbus_drv.c
> > @@ -36,6 +36,7 @@
> >   #include <linux/syscore_ops.h>
> >   #include <linux/dma-map-ops.h>
> >   #include <linux/pci.h>
> > +#include <linux/of_irq.h>
>
> If you are using this header in a driver, you are doing it wrong. We
> have common functions which work on both ACPI or DT, so use them if
> you have a need to support both.
Understood, thank you! I'll look more for the examples. If you happen to 
have in mind the place where the idiomatic/more preferred approach is 
used, please let me know, would owe you a great debt of gratitude.


> Though my first question on a binding will be the same as on every
> 'hypervisor binding'.  Why can't you make your hypervisor interfaces
> discoverable? It's all s/w, not some h/w device which is fixed.
I've taken a look at the related art. AWS's Firecracker, Intel's Cloud 
Hypervisor, Google's CrosVM, QEmu allow the guest use the 
well-established battle-tested generic approaches (ACPI, 
DeviceTree/OpenFirmware) of describing the virtual hardware and its 
resources rather than making the guest use their own specific 
interfaces. That holds true for the s/w devices like 
"vcpu-stall-detector" and VirtIO that do not have counterparts built as 
hardware, too.

Here, the guest needs to set up VMBus (the intra-partition communication 
transport) to be able to talk to the host partition. Receiving a message 
needs an interrupt service routine attached to the interrupt injected 
into the guest virtual processor, and DeviceTree lets provide the 
interrupt number. If a custom interface were used here, it'd look less 
expected due to others relying on ACPI and DT for configuring virtual 
devices and busses. A specialized interface would add more code (new 
code) instead of relying on the approach that is widely used.


> Rob

--
Thank you,
Roman