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

[Philipp Zabel <p.zabel@pengutronix.de>]

Hi Clément,

On Fr, 2022-04-08 at 17:48 +0200, Clément Léger 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.
> 
> Hi Rob,
> 
> I got something working (address translation, probing and so on) using
> what you started. I switch to using changeset however, I'm not sure that
> it make sense for property creation since the node has not yet been
> added to the tree. Attaching the node with changeset however seems
> to make sense. But I'm no expert here, so any advise is welcome.
>
> Based on what we said, I created a PCI driver which uses a builtin
> overlay. In order to be able to apply the overlay on the correct PCI
> node -the one on which the card was plugged) and thus be totally plug
> and play, the 'target-path' property is patched using direct fdt
> function and replaced the target with the PCI device node path.
> I don't see any other way to do that before applying the overlay since
> of_overlay_fdt_apply() takes a fdt blob as input.
> 
> The driver also insert correct ranges into the PCI device in order to
> translate the downstream node addresses to BAR addresses. It seems
> reasonnable to assume that this depends on the driver and thus should
> not be done by the PCI of core at all.
> 
> Finally, the driver probes the newly added childs using
> of_platform_populate(). With all of that, the address translation
> and the probing works correctly and the platform devices are created.
> There is still a few things to fix such as the following:
> 
> [ 2830.324773] OF: overlay: WARNING: memory leak will occur if overlay
> removed, property: /pci/pci@2,6/dev@0,0/compatible
> 
> But it seems like this is something that works and would allow to
> support various use cases. From what I see, it should also work on
> other platforms. Major advantage of that over fwnode is that the
> changes are pretty small and relatively contained.

Could you show this off somewhere?

From this I take that fwnode support in the reset subsystem is not of
use to you anymore. I'll postpone taking your patches then, until they
are needed.

regards
Philipp