linux-kernel - Re: Non-enumerable devices on USB and other enumerable buses

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Message-ID: <CACVXFVPFqHLQRpd0QBzoVapqHtKqrfGvWT0_nhXeFqjQVRsp5Q@mail.gmail.com>
Date:	Mon, 19 Aug 2013 20:17:53 +0800
From:	Ming Lei <tom.leiming@...il.com>
To:	Alan Stern <stern@...land.harvard.edu>
Cc:	Mark Brown <broonie@...nel.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Rob Herring <rob.herring@...xeda.com>,
	Pawel Moll <pawel.moll@....com>,
	Mark Rutland <mark.rutland@....com>,
	Stephen Warren <swarren@...dotorg.org>,
	Ian Campbell <ian.campbell@...rix.com>,
	Felipe Balbi <balbi@...com>,
	Grant Likely <grant.likely@...aro.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	linux-usb <linux-usb@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: Non-enumerable devices on USB and other enumerable buses

On Sat, Aug 17, 2013 at 9:29 AM, Alan Stern <stern@...land.harvard.edu> wrote:
> On Fri, 16 Aug 2013, Mark Brown wrote:
>
>> > Besides, you need to get the platform information to the driver in any
>> > case, no matter how you decide to solve the chicken-and-egg problem.
>> > It shouldn't be a factor in deciding which solution to use.
>>
>> It's not that this is hard, it's that I don't see how if you already
>> have some concept of the device in the kernel data structures (which you
>> must have in order to be able to provide platform data when it's needed)
>> anything is gained by not using that when dealing with bootstrapping
>> issues.
>
> I agree.  In fact, there's no choice but to use this device concept
> during startup.  Otherwise there's no way to get the platform data to
> the driver when it is needed, because there's no way to tell which
> device the data applies to.  The question is how elaborate the concept
> needs to be and how it gets used.
>
> Aong those lines, I would like to point out that the device concept
> embodied in the kernel's data structures can be pretty thin.  For
> example, it might be little more than a port number or bus address.

Maybe the principle behind drivers/usb/core/usb-acpi.c is helpful
for the problem, and DT may refer to ACPI to describe on-board
USB devices, and the way to retrieve platform data too.

>> Anyway, I think it's time to try to implement something rather than talk
>> about it.
>
> Hopefully this discussion has given you some ideas for alternative
> approachs, or at least helped to solidify your ideas.


Thanks,
-- 
Ming Lei
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