linux-kernel - Re: [RFC PATCH 06/10] usb: xhci: Add Tegra XHCI host-controller driver

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Message-ID: <11038777.juA2AddEko@wuerfel>
Date:	Thu, 15 May 2014 15:30:06 +0200
From:	Arnd Bergmann <arnd@...db.de>
To:	Thierry Reding <thierry.reding@...il.com>
Cc:	Andrew Bresticker <abrestic@...omium.org>,
	linux-tegra@...r.kernel.org, devicetree@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	linux-usb@...r.kernel.org, Rob Herring <robh+dt@...nel.org>,
	Pawel Moll <pawel.moll@....com>,
	Mark Rutland <mark.rutland@....com>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	Kumar Gala <galak@...eaurora.org>,
	Stephen Warren <swarren@...dotorg.org>,
	Russell King <linux@....linux.org.uk>,
	Peter De Schrijver <pdeschrijver@...dia.com>,
	Prashant Gaikwad <pgaikwad@...dia.com>,
	Mike Turquette <mturquette@...aro.org>,
	Kishon Vijay Abraham I <kishon@...com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Mathias Nyman <mathias.nyman@...el.com>,
	Grant Likely <grant.likely@...aro.org>,
	Randy Dunlap <rdunlap@...radead.org>
Subject: Re: [RFC PATCH 06/10] usb: xhci: Add Tegra XHCI host-controller driver

On Thursday 15 May 2014 11:19:40 Thierry Reding wrote:
> > > +
> > > +   xhci = platform_device_alloc("xhci-hcd", PLATFORM_DEVID_AUTO);
> > > +   if (!xhci) {
> > > +           dev_err(dev, "Failed to allocate XHCI host\n");
> > > +           ret = -ENOMEM;
> > > +           goto out;
> > > +   }
> > 
> > This does not feel appropriate at all: Rather than creating a child device,
> > you should have a specific driver that hooks into functions exported
> > by the xhci core. See Documentation/driver-model/design-patterns.txt
> 
> I don't think Documentation/driver-model/design-patterns.txt documents
> this. Perhaps this is what you had in mind?
> 
>         http://lwn.net/Articles/336262/

No, I did mean Documentation/driver-model/design-patterns.txt.

The pattern used in the proposed driver is to create the generic platform_device
as the child of the more specific platform_device.

The normal pattern is to have only one device and embed the generic structure
inside of the more specific structure and use container_of to cast between
the two as needed.

	Arnd
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