Date: Fri, 16 Aug 2013 21:00:09 +0100
From: Mark Brown <broonie@kernel.org>
To: Alan Stern <stern@rowland.harvard.edu>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Rob Herring <rob.herring@calxeda.com>, Pawel Moll <pawel.moll@arm.com>,
        Mark Rutland <mark.rutland@arm.com>,
        Stephen Warren <swarren@wwwdotorg.org>,
        Ian Campbell <ian.campbell@citrix.com>, Felipe Balbi <balbi@ti.com>,
        Grant Likely <grant.likely@linaro.org>, devicetree@vger.kernel.org,
        linux-usb@vger.kernel.org, linux-kernel@vger.kernel.org
Message-ID: <20130816200009.GU30073@sirena.org.uk>
References: <20130816183934.GQ30073@sirena.org.uk>
 <Pine.LNX.4.44L0.1308161457300.1532-100000@iolanthe.rowland.org>
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Subject: Re: Non-enumerable devices on USB and other enumerable buses
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On Fri, Aug 16, 2013 at 03:27:58PM -0400, Alan Stern wrote:
> On Fri, 16 Aug 2013, Mark Brown wrote:

> >  or those for getting platform data to a device when it
> > does enumerate.

> ?  I can't make any sense out of that comment.  For one thing, why do
> you need to send platform data to a device?  (It's obvious that a
> _driver_ would need to use platform data; it's not so clear that a
> _device_ would.)

The device in this context is a running instance of the driver.

> > > (The second proposal also has the advantage that the power-on code ma=
y=20
> > > be shared between the driver and the subsystem.)

> > Can you explain in more detail please, I don't follow?

> Let's say the subsystem powers up the device when the bus is first
> registered, so that the device can be detected and enumerated.  Let's
> also say that the driver wants to power-off and power-on the device
> from time to time, as part of normal runtime PM.  Then instead of
> having its own power-on routine (which would be code duplication), the
> driver can simply call the subsystem's power-on routine.  (Of course,
> this would mean that the routine would no longer be run-once.)

Oh, OK.  I don't think that's a meaningful difference, the driver is
going to have the code and be able to reuse it one way or another
anyway.  In many cases if the device has been in a low power idle mode a
slightly difference sequence would be needed anyway.

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