linux-kernel - Re: [PATCH v2 0/3] add fwnode support to reset subsystem

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Date:   Wed, 6 Apr 2022 15:33:46 +0200
From:   Alexandre Belloni <alexandre.belloni@...tlin.com>
To:     Rob Herring <robh@...nel.org>
Cc:     Clément Léger <clement.leger@...tlin.com>,
        Lizhi Hou <lizhi.hou@...inx.com>,
        Sonal Santan <sonal.santan@...inx.com>,
        Philipp Zabel <p.zabel@...gutronix.de>,
        Frank Rowand <frowand.list@...il.com>,
        Lars Povlsen <lars.povlsen@...rochip.com>,
        Steen Hegelund <Steen.Hegelund@...rochip.com>,
        Microchip Linux Driver Support <UNGLinuxDriver@...rochip.com>,
        Thomas Petazzoni <thomas.petazzoni@...tlin.com>,
        Allan Nielsen <allan.nielsen@...rochip.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        devicetree@...r.kernel.org,
        Stefano Stabellini <sstabellini@...nel.org>,
        Hans de Goede <hdegoede@...hat.com>,
        Mark Brown <broonie@...nel.org>
Subject: Re: [PATCH v2 0/3] add fwnode support to reset subsystem

On 06/04/2022 08:19:16-0500, Rob Herring wrote:
> > > > > 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.
> 

Last time I tried that, this was not working well because it means that
the ranges property of the device depends on the host machine...

-- 
Alexandre Belloni, co-owner and COO, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com