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Date:   Wed, 6 Apr 2022 08:19:16 -0500
From:   Rob Herring <robh@kernel.org>
To:     =?iso-8859-1?Q?Cl=E9ment_L=E9ger?= <clement.leger@bootlin.com>
Cc:     Lizhi Hou <lizhi.hou@xilinx.com>,
        Sonal Santan <sonal.santan@xilinx.com>,
        Philipp Zabel <p.zabel@pengutronix.de>,
        Frank Rowand <frowand.list@gmail.com>,
        Lars Povlsen <lars.povlsen@microchip.com>,
        Steen Hegelund <Steen.Hegelund@microchip.com>,
        Microchip Linux Driver Support <UNGLinuxDriver@microchip.com>,
        Thomas Petazzoni <thomas.petazzoni@bootlin.com>,
        Alexandre Belloni <alexandre.belloni@bootlin.com>,
        Allan Nielsen <allan.nielsen@microchip.com>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        devicetree@vger.kernel.org,
        Stefano Stabellini <sstabellini@kernel.org>,
        Hans de Goede <hdegoede@redhat.com>,
        Mark Brown <broonie@kernel.org>
Subject: Re: [PATCH v2 0/3] add fwnode support to reset subsystem
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On Wed, Apr 06, 2022 at 09:40:19AM +0200, Cl?ment L?ger wrote:
> Le Tue, 5 Apr 2022 12:11:51 -0500,
> Rob Herring <robh@kernel.org> a ?crit :
> 
> > On Tue, Apr 5, 2022 at 10:52 AM Cl?ment L?ger <clement.leger@bootlin.com> wrote:
> > >
> > > Le Tue, 5 Apr 2022 09:47:20 -0500,
> > > Rob Herring <robh@kernel.org> a ?crit :
> > >  
> 
> [...]
> 
> > >
> > > I also tried loading an overlay from a driver on an ACPI based system.
> > > Their patch is (I guess) targeting the specific problem that there is
> > > no base DT when using ACPI. However, Mark Brown feedback was not to
> > > mix OF and ACPI:  
> > 
> > I agree there. I don't think we should use DT bindings in ACPI tables
> > which is already happening. In this case, I think what's described by
> > ACPI and DT must be completely disjoint. I think that's the case here
> > as everything is downstream of the PCIe device.
> 
> Yes, there is no references to the host devices (at least in my case).
> 
> > 
> > > "That seems like it's opening a can of worms that might be best left
> > > closed."
> > >
> > > But I would be interested to know how the Xilinx guys are doing that
> > > on x86/ACPI based system.  
> > 
> > They aren't, yet...
> 
> Ok...
> 
> [...]
> 
> > 
> > 
> > > > I've told the Xilinx folks the same thing, but I would separate this
> > > > into 2 parts. First is just h/w work in a DT based system. Second is
> > > > creating a base tree an overlay can be applied to. The first part should
> > > > be pretty straightforward. We already have PCI bus bindings. The only
> > > > tricky part is getting address translation working from leaf device thru
> > > > the PCI bus to host bus, but support for that should all be in place
> > > > (given we support ISA buses off of PCI bus). The second part will
> > > > require generating PCI DT nodes at runtime. That may be needed for both
> > > > DT and ACPI systems as we don't always describe all the PCI hierarchy
> > > > in DT.  
> > >
> > > But then, if the driver generate the nodes, it will most probably
> > > have to describe the nodes by hardcoding them right ?  
> > 
> > No, the kernel already maintains its own tree of devices. You just
> > need to use that to generate the tree. That's really not much more
> > than nodes with a 'reg' property encoding the device and function
> > numbers.
> 
> Just to clarified a point, my PCI device exposes multiple peripherals
> behind one single PCI function.

Right. I would expect your PCI device DT node to have a 'simple-bus' 
child node with all those peripherals. And maybe there's other nodes 
like fixed-clocks, etc.

> To be sure I understood what you are suggesting, you propose to create
> a DT node from the PCI driver that has been probed dynamically
> matching this same PCI device with a 'reg' property. I also think
> this would requires to generate some 'pci-ranges' to remap the
> downstream devices that are described in the DTBO, finally, load the
> overlay to be apply under this newly created node. Is that right ?

Right. You'll need to take the BAR address(es) for the device and stick 
those into 'ranges' to translate offsets to BAR+offset.

Rob