linux-kernel - Re: ChipIdea USB regression

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Date:   Mon, 17 Jan 2022 09:55:59 +0000
From:   Charles Keepax <ckeepax@...nsource.cirrus.com>
To:     Rob Herring <robh@...nel.org>
CC:     Peter Chen <peter.chen@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Linux USB List <linux-usb@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Arnd Bergmann <arnd@...db.de>, Tony Lindgren <tony@...mide.com>
Subject: Re: ChipIdea USB regression

On Mon, Jan 17, 2022 at 09:26:56AM +0000, Charles Keepax wrote:
> On Sat, Jan 15, 2022 at 09:55:23AM -0600, Rob Herring wrote:
> > On Fri, Jan 14, 2022 at 5:18 AM Charles Keepax
> > <ckeepax@...nsource.cirrus.com> wrote:
> > > On Fri, Jan 14, 2022 at 10:56:20AM +0000, Charles Keepax wrote:
> > > So when that patch copies the DT node to the new platform device
> > > in ci_hdrc_add_device it copies the compatible stuff as well as
> > > the IRQ stuff it was targeting, this presumably causes the kernel
> > > to bind a new copy of the driver to that new device, which probes
> > > and calls ci_hdrc_add_device again repeating the process until
> > > it dies.
> > >
> > > Kinda looks to me like the best solution might just be to revert
> > > the patch, I am not sure I see how that copy of the DT is supposed
> > > to work?
> > 
> > It's not copying the DT, but yes AFAICT it does match and bind the
> > child device on the parent driver using the compatible match instead
> > of matching on driver name. I think we can use the of_reuse_node flag
> > to avoid this in the match, but that needs some more investigation.
> 
> Assuming you mean the of_node_reused flag, looks like it already
> being set, your code does this:
> 
> @@ -864,6 +864,7 @@ struct platform_device *ci_hdrc_add_device(struct device *dev,
> 	pdev->dev.parent = dev;
> 	+ device_set_of_node_from_dev(&pdev->dev, dev);
> 
> And that function does this:
> 
> void device_set_of_node_from_dev(struct device *dev, const struct device *dev2)
> {
> 	of_node_put(dev->of_node);
> 	dev->of_node = of_node_get(dev2->of_node);
> 	dev->of_node_reused = true;
> }
> EXPORT_SYMBOL_GPL(device_set_of_node_from_dev);
> 
> I guess maybe that flag doesn't do what it is supposed to for
> some reason?
> 

Ah ok it seems that flag is only currently used by the pinctrl
subsystem, didn't realise that was quite so new and not used
anywhere. I guess we probably need to add something to the
platform device code to use that flag too, if that is the way we
want to run with this.

Thanks,
Charles