netdev - Re: [PATCH 07/19] timberdale: mfd_cell is now implicitly available to drivers

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Message-ID: <20110407080921.GD29038@legolas.emea.dhcp.ti.com>
Date:	Thu, 7 Apr 2011 11:09:22 +0300
From:	Felipe Balbi <balbi@...com>
To:	Greg KH <gregkh@...e.de>
Cc:	Felipe Balbi <balbi@...com>, Samuel Ortiz <sameo@...ux.intel.com>,
	Grant Likely <grant.likely@...retlab.ca>,
	Andres Salomon <dilinger@...ued.net>,
	linux-kernel@...r.kernel.org,
	Mark Brown <broonie@...nsource.wolfsonmicro.com>,
	khali@...ux-fr.org, ben-linux@...ff.org,
	Peter Korsgaard <jacmet@...site.dk>,
	Mauro Carvalho Chehab <mchehab@...radead.org>,
	David Brownell <dbrownell@...rs.sourceforge.net>,
	linux-i2c@...r.kernel.org, linux-media@...r.kernel.org,
	netdev@...r.kernel.org, spi-devel-general@...ts.sourceforge.net,
	Mocean Laboratories <info@...ean-labs.com>
Subject: Re: [PATCH 07/19] timberdale: mfd_cell is now implicitly available
 to drivers

Hi,

On Wed, Apr 06, 2011 at 03:09:00PM -0700, Greg KH wrote:
> 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.

no problem.

ps: that's the driver for the USB3 controller which will come on OMAP5.
Driver being validate on a pre-silicon platform right now :-D In a few
weeks I'll send the driver for integration.

-- 
balbi
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