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

[Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>]

On Mon, Feb 17, 2020 at 12:35:12PM +0000, Pankaj Bansal wrote:
> 
> 
> > -----Original Message-----
> > From: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
> > Sent: Friday, February 14, 2020 11:20 PM
> > To: Pankaj Bansal <pankaj.bansal@nxp.com>
> > Cc: Marc Zyngier <maz@kernel.org>; Ard Biesheuvel
> > <ard.biesheuvel@linaro.org>; Makarand Pawagi <makarand.pawagi@nxp.com>;
> > Calvin Johnson <calvin.johnson@nxp.com>; stuyoder@gmail.com;
> > nleeder@codeaurora.org; Ioana Ciornei <ioana.ciornei@nxp.com>; Cristi
> > Sovaiala <cristian.sovaiala@nxp.com>; Hanjun Guo <guohanjun@huawei.com>;
> > Will Deacon <will@kernel.org>; jon@solid-run.com; Russell King
> > <linux@armlinux.org.uk>; ACPI Devel Maling List <linux-acpi@vger.kernel.org>;
> > Len Brown <lenb@kernel.org>; Jason Cooper <jason@lakedaemon.net>; Andy
> > Wang <Andy.Wang@arm.com>; Varun Sethi <V.Sethi@nxp.com>; Thomas
> > Gleixner <tglx@linutronix.de>; linux-arm-kernel <linux-arm-
> > kernel@lists.infradead.org>; Laurentiu Tudor <laurentiu.tudor@nxp.com>; Paul
> > Yang <Paul.Yang@arm.com>; netdev@vger.kernel.org; Rafael J. Wysocki
> > <rjw@rjwysocki.net>; Linux Kernel Mailing List <linux-kernel@vger.kernel.org>;
> > Shameerali Kolothum Thodi <shameerali.kolothum.thodi@huawei.com>;
> > Sudeep Holla <sudeep.holla@arm.com>; Robin Murphy
> > <robin.murphy@arm.com>
> > Subject: Re: [EXT] Re: [PATCH] bus: fsl-mc: Add ACPI support for fsl-mc
> > 
> > On Fri, Feb 14, 2020 at 04:35:10PM +0000, Pankaj Bansal wrote:
> > 
> > [...]
> > 
> > > > -----Original Message-----
> > > > From: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
> > > > Sent: Friday, February 14, 2020 9:50 PM
> > > > To: Pankaj Bansal <pankaj.bansal@nxp.com>
> > > > Cc: Marc Zyngier <maz@kernel.org>; Ard Biesheuvel
> > > > <ard.biesheuvel@linaro.org>; Makarand Pawagi
> > <makarand.pawagi@nxp.com>;
> > > > Calvin Johnson <calvin.johnson@nxp.com>; stuyoder@gmail.com;
> > > > nleeder@codeaurora.org; Ioana Ciornei <ioana.ciornei@nxp.com>; Cristi
> > > > Sovaiala <cristian.sovaiala@nxp.com>; Hanjun Guo
> > <guohanjun@huawei.com>;
> > > > Will Deacon <will@kernel.org>; jon@solid-run.com; Russell King
> > > > <linux@armlinux.org.uk>; ACPI Devel Maling List <linux-
> > acpi@vger.kernel.org>;
> > > > Len Brown <lenb@kernel.org>; Jason Cooper <jason@lakedaemon.net>;
> > Andy
> > > > Wang <Andy.Wang@arm.com>; Varun Sethi <V.Sethi@nxp.com>; Thomas
> > > > Gleixner <tglx@linutronix.de>; linux-arm-kernel <linux-arm-
> > > > kernel@lists.infradead.org>; Laurentiu Tudor <laurentiu.tudor@nxp.com>;
> > Paul
> > > > Yang <Paul.Yang@arm.com>; netdev@vger.kernel.org; Rafael J. Wysocki
> > > > <rjw@rjwysocki.net>; Linux Kernel Mailing List <linux-
> > kernel@vger.kernel.org>;
> > > > Shameerali Kolothum Thodi <shameerali.kolothum.thodi@huawei.com>;
> > > > Sudeep Holla <sudeep.holla@arm.com>; Robin Murphy
> > > > <robin.murphy@arm.com>
> > > > Subject: Re: [EXT] Re: [PATCH] bus: fsl-mc: Add ACPI support for fsl-mc
> > Side note: would you mind removing the email headers (as above) in your
> > replies please ?

Read the question above please.

[...]

> > > 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.

> And IORT layer ought to retrieve the output id based on single ID mapping flag as well as input id.
> 
> > 
> > Side note: can you explain to me please how the MSI allocation flow
> > and kernel data structures/drivers are modeled in DT ? I had a quick
> > look at:
> > 
> > drivers/irqchip/irq-gic-v3-its-fsl-mc-msi.c
> > 
> > and to start with, does that code imply that we create a
> > DOMAIN_BUS_FSL_MC_MSI on ALL DT systems with an ITS device node ?
> 
> Yes. It's being done for all DT systems having ITS node.

This does not seem correct to me, I will let Marc comment on
the matter.

> The domain creation is handled in drivers/bus/fsl-mc/fsl-mc-msi.c

Thanks,
Lorenzo