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

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Date:	Fri, 1 Apr 2011 12:00:57 -0600
From:	Grant Likely <grant.likely@...retlab.ca>
To:	Andres Salomon <dilinger@...ued.net>
Cc:	Samuel Ortiz <sameo@...ux.intel.com>, 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>,
	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 1, 2011 at 11:56 AM, Grant Likely <grant.likely@...retlab.ca> 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.
>
> One last option is I'm prototyping a way to add type-safe structure
> pointers to a device, but that requires nasty CPP tricks and it's not
> complete yet.  The cure might be worse than the disease here.

And yet another option is to create a mfd_bus_type, but that probably
isn't helpful since the one of the purposes of MFDs is that it is a
collection of non-detectable memory mapped devices that
platform_bus_type is intended to handle.

g.
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