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: <YCV+7z8Y/l0eyse9@google.com>
Date:   Thu, 11 Feb 2021 11:01:03 -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()

On Thu, Feb 11, 2021 at 10:45:48AM -0800, Matthias Kaehlcke wrote:
> 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.

To let the xhci-plat driver create the platform device was suggested by Alan:

https://lore.kernel.org/patchwork/patch/1313000/#1510227

Personally I would favor a standalone platform device, since it provides more
flexiblity (also works for hubs connected to a non-root hub) and doesn't require
cooperation from other driver, however I doubt I could convince Rob of the
corresponding DT bindings.