linux-kernel - Re: [PATCH v5 3/4] usb: host: xhci-plat: Create platform device for onboard hubs in probe()

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Message-ID: <YCV7XGloQIjtFAqf@google.com>
Date:   Thu, 11 Feb 2021 10:45:48 -0800
From:   Matthias Kaehlcke <mka@...omium.org>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     Rob Herring <robh+dt@...nel.org>,
        Frank Rowand <frowand.list@...il.com>,
        devicetree@...r.kernel.org, Peter Chen <peter.chen@....com>,
        Stephen Boyd <swboyd@...omium.org>,
        Alan Stern <stern@...land.harvard.edu>,
        Ravi Chandra Sadineni <ravisadineni@...omium.org>,
        Bastien Nocera <hadess@...ess.net>,
        linux-kernel@...r.kernel.org,
        Douglas Anderson <dianders@...omium.org>,
        linux-usb@...r.kernel.org, Krzysztof Kozlowski <krzk@...nel.org>,
        Mathias Nyman <mathias.nyman@...el.com>
Subject: Re: [PATCH v5 3/4] usb: host: xhci-plat: Create platform device for
 onboard hubs in probe()

Hi Greg,

On Thu, Feb 11, 2021 at 07:58:23AM +0100, Greg Kroah-Hartman wrote:
> On Wed, Feb 10, 2021 at 09:10:38AM -0800, Matthias Kaehlcke wrote:
> > Check during probe() if a hub supported by the onboard_usb_hub
> > driver is connected to the controller. If such a hub is found
> > create the corresponding platform device. This requires the
> > device tree to have a node for the hub with its vendor and
> > product id (which is not common for USB devices). Further the
> > platform device is only created when CONFIG_USB_ONBOARD_HUB=y/m.
> > 
> > Signed-off-by: Matthias Kaehlcke <mka@...omium.org>
> > ---
> > 
> > Changes in v5:
> > - patch added to the series
> > 
> >  drivers/usb/host/xhci-plat.c | 16 ++++++++++++++++
> >  include/linux/usb/hcd.h      |  2 ++
> >  2 files changed, 18 insertions(+)
> > 
> > diff --git a/drivers/usb/host/xhci-plat.c b/drivers/usb/host/xhci-plat.c
> > index 4d34f6005381..e785fa109eea 100644
> > --- a/drivers/usb/host/xhci-plat.c
> > +++ b/drivers/usb/host/xhci-plat.c
> > @@ -15,6 +15,7 @@
> >  #include <linux/of.h>
> >  #include <linux/of_device.h>
> >  #include <linux/platform_device.h>
> > +#include <linux/usb/onboard_hub.h>
> >  #include <linux/usb/phy.h>
> >  #include <linux/slab.h>
> >  #include <linux/acpi.h>
> > @@ -184,6 +185,7 @@ static int xhci_plat_probe(struct platform_device *pdev)
> >  	int			ret;
> >  	int			irq;
> >  	struct xhci_plat_priv	*priv = NULL;
> > +	struct device_node	*np;
> >  
> >  
> >  	if (usb_disabled())
> > @@ -356,6 +358,17 @@ static int xhci_plat_probe(struct platform_device *pdev)
> >  	 */
> >  	pm_runtime_forbid(&pdev->dev);
> >  
> > +	np = usb_of_get_device_node(hcd->self.root_hub, hcd->self.busnum);
> > +	if (np && of_is_onboard_usb_hub(np)) {
> > +		struct platform_device *pdev;
> > +
> > +		pdev = of_platform_device_create(np, NULL, NULL);
> 
> A platform device is a child of another platform device?  Ok, but
> really, why?  What uses this device?

In earlier versions there was a standalone platform device:
https://lore.kernel.org/patchwork/patch/1313001/

However this was rejected by Rob, since the DT would require a node for the
platform device and (implicit or explicit) nodes for the USB devices,
representing the same physical device:

https://lore.kernel.org/patchwork/patch/1305395/
https://lore.kernel.org/patchwork/patch/1313000/

Both Doug Anderson and myself argued that it seems legitimate to distinguish
between the devices connected to the USB bus, and the chip which might have
GPIOs, regulators, clocks, ... but apparently our arguments were not
convincing enough.