RE: [PATCH] bus: fsl-mc: Add ACPI support for fsl-mc

From: Pankaj Bansal (OSS)
Date: Tue Feb 18 2020 - 07:48:47 EST

> >>>>> As stated above, in Linux MC is a bus (just like PCI bus, AMBA bus etc)
> >>>>> There can be multiple devices attached to this bus. Moreover, we can
> >>>> dynamically create/destroy these devices.
> >>>>> Now, we want to represent this BUS (not individual devices connected to
> >> bus)
> >>>> in IORT table.
> >>>>> The only possible way right now we see is that we describe it as Named
> >>>> components having a pool of ID mappings.
> >>>>> As and when devices are created and attached to bus, we sift through this
> >> pool
> >>>> to correctly determine the output ID for the device.
> >>>>> Now the input ID that we provide, can come from device itself.
> >>>>> Then we can use the Platform MSI framework for MC bus devices.
> >>>>
> >>>> So are you asking me if that's OK ? Or there is something you can't
> >>>> describe with IORT ?
> >>>
> >>> I am asking if that would be acceptable?
> >>> i.e. we represent MC bus as Named component is IORT table with a pool of
> IDs
> >> (without single ID mapping flag)
> >>> and then we use the Platform MSI framework for all children devices of MC
> >> bus.
> >>> Note that it would require the Platform MSI layer to correctly pass an input
> id
> >> for a platform device to IORT layer.
> >>
> >> How is this solved in DT ? You don't seem to need any DT binding on top
> >> of the msi-parent property, which is equivalent to IORT single mappings
> >> AFAICS so I would like to understand the whole DT flow (so that I
> >> understand how this FSL bus works) before commenting any further.
> >
> > In DT case, we create the domain DOMAIN_BUS_FSL_MC_MSI for MC bus and
> it's children.
> > And then when MC child device is created, we search the "msi-parent"
> property from the MC
> > DT node and get the ITS associated with MC bus. Then we search
> > on that ITS. Once we find the domain, we can call msi_domain_alloc_irqs for
> that domain.
> >
> > This is exactly what we tried to do initially with ACPI. But the searching
> > associated to an ITS, is something that is part of drivers/acpi/arm64/iort.c.
> Can you have a look at mbigen driver (drivers/irqchip/irq-mbigen.c) to see if
> it helps you?
> mbigen is an irq converter to convert device's wired interrupts into MSI
> (connecting to ITS), which will alloc a bunch of MSIs from ITS platform MSI
> domain at the setup.

Unfortunately this is not the same case as ours. As I see Hisilicon IORT table
Is using single id mapping with named components.

while we are not:

This is because as I said, we are trying to represent a bus in IORT via named components and
not individual devices connected to that bus.

> Thanks
> Hanjun