Date: Wed, 6 Apr 2011 15:09:00 -0700
From: Greg KH <gregkh@suse.de>
To: Felipe Balbi <balbi@ti.com>
Cc: Samuel Ortiz <sameo@linux.intel.com>,
        Grant Likely <grant.likely@secretlab.ca>,
        Andres Salomon <dilinger@queued.net>, linux-kernel@vger.kernel.org,
        Mark Brown <broonie@opensource.wolfsonmicro.com>, khali@linux-fr.org,
        ben-linux@fluff.org, Peter Korsgaard <jacmet@sunsite.dk>,
        Mauro Carvalho Chehab <mchehab@infradead.org>,
        David Brownell <dbrownell@users.sourceforge.net>,
        linux-i2c@vger.kernel.org, linux-media@vger.kernel.org,
        netdev@vger.kernel.org, spi-devel-general@lists.sourceforge.net,
        Mocean Laboratories <info@mocean-labs.com>
Subject: Re: [PATCH 07/19] timberdale: mfd_cell is now implicitly available
 to drivers
Message-ID: <20110406220900.GA16117@suse.de>
References: <20110401235239.GE29397@sortiz-mobl>
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 <20110404100314.GC2751@sortiz-mobl>
 <20110405030428.GB29522@ponder.secretlab.ca>
 <20110406152322.GA2757@sortiz-mobl>
 <20110406155805.GA20095@suse.de>
 <20110406170537.GB2757@sortiz-mobl>
 <20110406175647.GA8048@suse.de>
 <20110406184733.GD2757@sortiz-mobl>
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On Wed, Apr 06, 2011 at 09:59:02PM +0300, Felipe Balbi wrote:
> Hi,
> 
> On Wed, Apr 06, 2011 at 08:47:34PM +0200, Samuel Ortiz wrote:
> > > > > What is a "MFD cell pointer" and why is it needed in struct device?
> > > > An MFD cell is an MFD instantiated device.
> > > > MFD (Multi Function Device) drivers instantiate platform devices. Those
> > > > devices drivers sometimes need a platform data pointer, sometimes an MFD
> > > > specific pointer, and sometimes both. Also, some of those drivers have been
> > > > implemented as MFD sub drivers, while others know nothing about MFD and just
> > > > expect a plain platform_data pointer.
> > > 
> > > That sounds like a bug in those drivers, why not fix them to properly
> > > pass in the correct pointer?
> > Because they're drivers for generic IPs, not MFD ones. By forcing them to use
> > MFD specific structure and APIs, we make it more difficult for platform code
> > to instantiate them.
> 
> I agree. What I do on those cases is to have a simple platform_device
> for the core IP driver and use platform_device_id tables to do runtime
> checks of the small differences. If one platform X doesn't use a
> platform_bus, it uses e.g. PCI, then you make a PCI "bridge" which
> allocates a platform_device with the correct name and adds that to the
> driver model.
> 
> See [1] (for the core driver) and [2] (for a PCI bridge driver) for an
> example of what I'm talking about.

Yes, thanks for providing a real example, this is the best way to handle
this.

thanks,

greg k-h
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