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

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Date:	Fri, 1 Apr 2011 17:58:44 -0600
From:	Grant Likely <grant.likely@...retlab.ca>
To:	Samuel Ortiz <sameo@...ux.intel.com>
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>,
	Greg Kroah-Hartman <gregkh@...e.de>
Subject: Re: [PATCH 07/19] timberdale: mfd_cell is now implicitly available to drivers

On Fri, Apr 1, 2011 at 5:52 PM, Samuel Ortiz <sameo@...ux.intel.com> wrote:
> 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.

[cc'ing gregkh because we're talking about modifying struct platform_device]

I'll back you up on this one.  It is a far better solution than the
alternatives.  At least with mfd, it covers a large set of devices.  I
think there is a strong argument for doing this.  Or alternatively,
the particular interesting fields from mfd_cell could be added to
platform_device.  What information do child devices need access to?

g.
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