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

On Fri, 1 Apr 2011 17:58:44 -0600
Grant Likely [off-list ref] wrote:

On Fri, Apr 1, 2011 at 5:52 PM, Samuel Ortiz [off-list ref]
wrote:

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On Fri, Apr 01, 2011 at 11:56:35AM -0600, Grant Likely wrote:

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On Fri, Apr 1, 2011 at 11:47 AM, Andres Salomon
[off-list ref] wrote:

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On Fri, 1 Apr 2011 13:20:31 +0200
Samuel Ortiz [off-list ref] wrote:

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Hi Grant,

On Thu, Mar 31, 2011 at 05:05:22PM -0600, Grant Likely wrote:

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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?

This was one of the things I was originally tempted to do (adding
mfd fields to platform_device).  I didn't think it would fly.

I can look at this stuff or help out once I have a stable internet
connection and I'm all moved in to my new place (which should be
Wednesday).