Re: [PATCH] usb: dwc3: host: inherit dma configuration from parent dev - Russell King

From: Russell King - ARM Linux <linux@armlinux.org.uk>
To: Peter Chen <hzpeterchen@gmail.com>
Cc: Arnd Bergmann <arnd@arndb.de>, Felipe Balbi <balbi@kernel.org>,
	Leo Li <pku.leo@gmail.com>,
	Grygorii Strashko <grygorii.strashko@ti.com>,
	Catalin Marinas <catalin.marinas@arm.com>,
	Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>,
	"linux-usb@vger.kernel.org" <linux-usb@vger.kernel.org>,
	Sekhar Nori <nsekhar@ti.com>, lkml <linux-kernel@vger.kernel.org>,
	Stuart Yoder <stuart.yoder@nxp.com>,
	Scott Wood <oss@buserror.net>,
	David Fisher <david.fisher1@synopsys.com>,
	"Thang Q. Nguyen" <tqnguyen@apm.com>,
	Alan Stern <stern@rowland.harvard.edu>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	"linux-arm-kernel@lists.infradead.org" 
	<linux-arm-kernel@lists.infradead.org>
Subject: Re: [PATCH] usb: dwc3: host: inherit dma configuration from parent dev
Date: Wed, 7 Sep 2016 10:35:26 +0100	[thread overview]
Message-ID: <20160907093525.GK1041@n2100.armlinux.org.uk> (raw)
In-Reply-To: <20160907092901.GC13903@b29397-desktop>

On Wed, Sep 07, 2016 at 05:29:01PM +0800, Peter Chen wrote:
> On Wed, Sep 07, 2016 at 10:52:46AM +0200, Arnd Bergmann wrote:
> > On Wednesday, September 7, 2016 3:44:28 PM CEST Peter Chen wrote:
> > > 
> > > The pre-condition of DT function at USB HCD core works is the host
> > > controller device has of_node, since it is the root node for USB tree
> > > described at DT. If the host controller device is not at DT, it needs
> > > to try to get its of_node, the chipidea driver gets it through its
> > > parent node [1]
> > 
> > > 
> > > [1] https://lkml.org/lkml/2016/8/8/119
> > > 
> > 
> > Ah, this is what I was referring to in the other mail.
> > 
> > However, the way you set the of_node might be dangerous too:
> > We should generally not have two platform_device structures with
> > the same of_node pointer, most importantly it may cause the
> > child device to be bound to the same driver as the parent
> > device since the probing is done by compatible string.
> > 
> > As you tested it successfully, it must work at the moment on your
> > machine, but it could easily break depending on deferred probing
> > or module load order.
> > 
> 
> Currently, I work around above problems by setting core device of_node
> as NULL at both probe error path and platform driver .remove routine.
> 
> I admit it is not a good way, but if we only have of_node at device's
> life periods after probe, it seems ok currently. It is hard to create
> of_node dynamically when create device, and keep some contents
> of parent's of_node, and some are not.

How about turning dwc3 into a library which can be used by a range of
platform devices?  Wouldn't that solve all the current problems, and
completely avoid the need to copy resources from one platform device
to another?

-- 
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