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Date:   Mon, 17 Feb 2020 15:25:18 +0000
From:   Lorenzo Pieralisi <lorenzo.pieralisi@....com>
To:     Pankaj Bansal <pankaj.bansal@....com>
Cc:     Marc Zyngier <maz@...nel.org>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        Makarand Pawagi <makarand.pawagi@....com>,
        Calvin Johnson <calvin.johnson@....com>,
        "stuyoder@...il.com" <stuyoder@...il.com>,
        "nleeder@...eaurora.org" <nleeder@...eaurora.org>,
        Ioana Ciornei <ioana.ciornei@....com>,
        Cristi Sovaiala <cristian.sovaiala@....com>,
        Hanjun Guo <guohanjun@...wei.com>,
        Will Deacon <will@...nel.org>,
        "jon@...id-run.com" <jon@...id-run.com>,
        Russell King <linux@...linux.org.uk>,
        ACPI Devel Maling List <linux-acpi@...r.kernel.org>,
        Len Brown <lenb@...nel.org>,
        Jason Cooper <jason@...edaemon.net>,
        Andy Wang <Andy.Wang@....com>, Varun Sethi <V.Sethi@....com>,
        Thomas Gleixner <tglx@...utronix.de>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        Laurentiu Tudor <laurentiu.tudor@....com>,
        Paul Yang <Paul.Yang@....com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Shameerali Kolothum Thodi 
        <shameerali.kolothum.thodi@...wei.com>,
        Sudeep Holla <sudeep.holla@....com>,
        Robin Murphy <robin.murphy@....com>
Subject: Re: [EXT] Re: [PATCH] bus: fsl-mc: Add ACPI support for fsl-mc

On Mon, Feb 17, 2020 at 12:35:12PM +0000, Pankaj Bansal wrote:
> 
> 
> > -----Original Message-----
> > From: Lorenzo Pieralisi <lorenzo.pieralisi@....com>
> > Sent: Friday, February 14, 2020 11:20 PM
> > To: Pankaj Bansal <pankaj.bansal@....com>
> > Cc: Marc Zyngier <maz@...nel.org>; Ard Biesheuvel
> > <ard.biesheuvel@...aro.org>; Makarand Pawagi <makarand.pawagi@....com>;
> > Calvin Johnson <calvin.johnson@....com>; stuyoder@...il.com;
> > nleeder@...eaurora.org; Ioana Ciornei <ioana.ciornei@....com>; Cristi
> > Sovaiala <cristian.sovaiala@....com>; Hanjun Guo <guohanjun@...wei.com>;
> > Will Deacon <will@...nel.org>; jon@...id-run.com; Russell King
> > <linux@...linux.org.uk>; ACPI Devel Maling List <linux-acpi@...r.kernel.org>;
> > Len Brown <lenb@...nel.org>; Jason Cooper <jason@...edaemon.net>; Andy
> > Wang <Andy.Wang@....com>; Varun Sethi <V.Sethi@....com>; Thomas
> > Gleixner <tglx@...utronix.de>; linux-arm-kernel <linux-arm-
> > kernel@...ts.infradead.org>; Laurentiu Tudor <laurentiu.tudor@....com>; Paul
> > Yang <Paul.Yang@....com>; netdev@...r.kernel.org; Rafael J. Wysocki
> > <rjw@...ysocki.net>; Linux Kernel Mailing List <linux-kernel@...r.kernel.org>;
> > Shameerali Kolothum Thodi <shameerali.kolothum.thodi@...wei.com>;
> > Sudeep Holla <sudeep.holla@....com>; Robin Murphy
> > <robin.murphy@....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@....com>
> > > > Sent: Friday, February 14, 2020 9:50 PM
> > > > To: Pankaj Bansal <pankaj.bansal@....com>
> > > > Cc: Marc Zyngier <maz@...nel.org>; Ard Biesheuvel
> > > > <ard.biesheuvel@...aro.org>; Makarand Pawagi
> > <makarand.pawagi@....com>;
> > > > Calvin Johnson <calvin.johnson@....com>; stuyoder@...il.com;
> > > > nleeder@...eaurora.org; Ioana Ciornei <ioana.ciornei@....com>; Cristi
> > > > Sovaiala <cristian.sovaiala@....com>; Hanjun Guo
> > <guohanjun@...wei.com>;
> > > > Will Deacon <will@...nel.org>; jon@...id-run.com; Russell King
> > > > <linux@...linux.org.uk>; ACPI Devel Maling List <linux-
> > acpi@...r.kernel.org>;
> > > > Len Brown <lenb@...nel.org>; Jason Cooper <jason@...edaemon.net>;
> > Andy
> > > > Wang <Andy.Wang@....com>; Varun Sethi <V.Sethi@....com>; Thomas
> > > > Gleixner <tglx@...utronix.de>; linux-arm-kernel <linux-arm-
> > > > kernel@...ts.infradead.org>; Laurentiu Tudor <laurentiu.tudor@....com>;
> > Paul
> > > > Yang <Paul.Yang@....com>; netdev@...r.kernel.org; Rafael J. Wysocki
> > > > <rjw@...ysocki.net>; Linux Kernel Mailing List <linux-
> > kernel@...r.kernel.org>;
> > > > Shameerali Kolothum Thodi <shameerali.kolothum.thodi@...wei.com>;
> > > > Sudeep Holla <sudeep.holla@....com>; Robin Murphy
> > > > <robin.murphy@....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

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