Re: [PATCH] mfd: Add Simple PCI MFD driver

Vincent Whitchurch
2023-01-23T16:02:52Z

On Mon, Jan 23, 2023 at 04:32:55PM +0100, Lee Jones wrote:
> On Mon, 23 Jan 2023, Vincent Whitchurch wrote:
> > Add a PCI driver which registers all child nodes specified in the
> > devicetree. It will allow platform devices to be used on virtual
> > systems which already support PCI and devicetree, such as UML with
> > virt-pci.
> >
> > The driver has no id_table by default; user space needs to provide one
> > using the new_id mechanism in sysfs.
>
> This feels wrong for several reasons.
>
> Firstly, I think Greg (Cc:ed) will have something to say about this.
>
> Secondly, this driver does literally nothing.

Well, it does do what the commit message says. If there's another way
of accomplishing that, I'm all ears.

> Why can't you use of of the other, pre-existing "also register my
> children" compatibles?
>
> See: drivers/bus/simple-pm-bus.c
> drivers/of/platform.c

simple-pm-bus registers a platform driver, and drivers/of/platform.c
works on the platform bus. The driver added by this patch is a PCI
driver. So I don't understand how the files you mention could be used
here?

In case it helps, the relevant nodes in my UML devicetree look something
like this:

virtio@2 {
compatible = "virtio,uml";
virtio-device-id = <1234>;
ranges;

pci {
#address-cells = <3>;
#size-cells = <2>;
ranges = <0x0000000 0 0 0 0xf0000000 0 0x20000>;
compatible = "virtio,device4d2", "pci";
device_type = "pci";
bus-range = <0 0>;

platform_parent: device@0,0 {
compatible = "pci494f,dc8";
reg = <0x00000 0 0 0x0 0x10000>;
ranges;

uart@10000 {
compatible = "google,goldfish-tty";
reg = <0x00000 0 0x10000 0 0x10000>;
};
};
};
};