Re: [RFC PATCH V1 05/12] hvm/dm: Introduce xendevicemodel_set_irq_level DM op

[Stefano Stabellini <sstabellini@kernel.org>]

On Wed, 5 Aug 2020, Julien Grall wrote:
> On 05/08/2020 00:22, Stefano Stabellini wrote:
> > On Mon, 3 Aug 2020, Oleksandr Tyshchenko wrote:
> > > From: Oleksandr Tyshchenko <oleksandr_tyshchenko@epam.com>
> > > 
> > > This patch adds ability to the device emulator to notify otherend
> > > (some entity running in the guest) using a SPI and implements Arm
> > > specific bits for it. Proposed interface allows emulator to set
> > > the logical level of a one of a domain's IRQ lines.
> > > 
> > > Please note, this is a split/cleanup of Julien's PoC:
> > > "Add support for Guest IO forwarding to a device emulator"
> > > 
> > > Signed-off-by: Julien Grall <julien.grall@arm.com>
> > > Signed-off-by: Oleksandr Tyshchenko <oleksandr_tyshchenko@epam.com>
> > > ---
> > >   tools/libs/devicemodel/core.c                   | 18 ++++++++++++++++++
> > >   tools/libs/devicemodel/include/xendevicemodel.h |  4 ++++
> > >   tools/libs/devicemodel/libxendevicemodel.map    |  1 +
> > >   xen/arch/arm/dm.c                               | 22
> > > +++++++++++++++++++++-
> > >   xen/common/hvm/dm.c                             |  1 +
> > >   xen/include/public/hvm/dm_op.h                  | 15 +++++++++++++++
> > >   6 files changed, 60 insertions(+), 1 deletion(-)
> > > 
> > > diff --git a/tools/libs/devicemodel/core.c b/tools/libs/devicemodel/core.c
> > > index 4d40639..30bd79f 100644
> > > --- a/tools/libs/devicemodel/core.c
> > > +++ b/tools/libs/devicemodel/core.c
> > > @@ -430,6 +430,24 @@ int xendevicemodel_set_isa_irq_level(
> > >       return xendevicemodel_op(dmod, domid, 1, &op, sizeof(op));
> > >   }
> > >   +int xendevicemodel_set_irq_level(
> > > +    xendevicemodel_handle *dmod, domid_t domid, uint32_t irq,
> > > +    unsigned int level)
> > 
> > It is a pity that having xen_dm_op_set_pci_intx_level and
> > xen_dm_op_set_isa_irq_level already we need to add a third one, but from
> > the names alone I don't think we can reuse either of them.
> 
> The problem is not the name...
> 
> > 
> > It is very similar to set_isa_irq_level. We could almost rename
> > xendevicemodel_set_isa_irq_level to xendevicemodel_set_irq_level or,
> > better, just add an alias to it so that xendevicemodel_set_irq_level is
> > implemented by calling xendevicemodel_set_isa_irq_level. Honestly I am
> > not sure if it is worth doing it though. Any other opinions?
> 
> ... the problem is the interrupt field is only 8-bit. So we would only be able
> to cover IRQ 0 - 255.

Argh, that's not going to work :-(  I wasn't sure if it was a good idea
anyway.


> It is not entirely clear how the existing subop could be extended without
> breaking existing callers.
>
> > But I think we should plan for not needing two calls (one to set level
> > to 1, and one to set it to 0):
> > https://marc.info/?l=xen-devel&m=159535112027405
> 
> I am not sure to understand your suggestion here? Are you suggesting to remove
> the 'level' parameter?

My hope was to make it optional to call the hypercall with level = 0,
not necessarily to remove 'level' from the struct.