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

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Message-ID: <20200214174949.GA30484@e121166-lin.cambridge.arm.com>
Date:   Fri, 14 Feb 2020 17:49:49 +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 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 ?

> > On Fri, Feb 14, 2020 at 03:58:14PM +0000, Pankaj Bansal wrote:
> > 
> > [...]
> > 
> > > > Why should the device know about its own ID? That's a bus/interconnect
> > thing.
> > > > And nothing should be passed *to* IORT. IORT is the source.
> > >
> > > IORT is translation between Input IDs <-> Output IDs. The Input ID is still
> > expected to be passed to parse IORT table.
> > 
> > Named components use an array of single mappings (as in entries with single
> > mapping flag set) - Input ID is irrelevant.
> > 
> > Not sure what your named component is though and what you want to do with
> > it, the fact that IORT allows mapping for named components do not necessarily
> > mean that it can describe what your system really is, on that you need to
> > elaborate for us to be able to help.
> 
> Details about MC bus can be read from here:
> https://elixir.bootlin.com/linux/latest/source/Documentation/networking/device_drivers/freescale/dpaa2/overview.rst#L324
> 
> 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 ?

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 ?

I *think* you have a specific API to allocate MSIs for MC devices:

fsl_mc_msi_domain_alloc_irqs()

which hook into the IRQ domain created in the file above that handles
the cascading to an ITS domain, correct ?

Thanks,
Lorenzo