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

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Date:	Sat, 2 Apr 2011 01:52:39 +0200
From:	Samuel Ortiz <sameo@...ux.intel.com>
To:	Grant Likely <grant.likely@...retlab.ca>
Cc:	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

On Fri, Apr 01, 2011 at 11:56:35AM -0600, Grant Likely wrote:
> On Fri, Apr 1, 2011 at 11:47 AM, Andres Salomon <dilinger@...ued.net> wrote:
> > On Fri, 1 Apr 2011 13:20:31 +0200
> > Samuel Ortiz <sameo@...ux.intel.com> wrote:
> >
> >> Hi Grant,
> >>
> >> On Thu, Mar 31, 2011 at 05:05:22PM -0600, Grant Likely wrote:
> > [...]
> >> > Gah.  Not all devices instantiated via mfd will be an mfd device,
> >> > which means that the driver may very well expect an *entirely
> >> > different* platform_device pointer; which further means a very high
> >> > potential of incorrectly dereferenced structures (as evidenced by a
> >> > patch series that is not bisectable).  For instance, the xilinx ip
> >> > cores are used by more than just mfd.
> >> I agree. Since the vast majority of the MFD subdevices are MFD
> >> specific IPs, I overlooked that part. The impacted drivers are the
> >> timberdale and the DaVinci voice codec ones.
> 
> Another option is you could do this for MFD devices:
> 
> struct mfd_device {
>         struct platform_devce pdev;
>         struct mfd_cell *cell;
> };
> 
> However, that requires that drivers using the mfd_cell will *never*
> get instantiated outside of the mfd infrastructure, and there is no
> way to protect against this so it is probably a bad idea.
> 
> Or, mfd_cell could be added to platform_device directly which would
> *by far* be the safest option at the cost of every platform_device
> having a mostly unused mfd_cell pointer.  Not a significant cost in my
> opinion.
I thought about this one, but I had the impression people would want to kill
me for adding an MFD specific pointer to platform_device. I guess it's worth
giving it a try since it would be a simple and safe solution.
I'll look at it later this weekend.

Thanks for the input.

Cheers,
Samuel.

-- 
Intel Open Source Technology Centre
http://oss.intel.com/
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