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    SubjectRe: [PATCH 07/19] timberdale: mfd_cell is now implicitly available to drivers
    On Fri, Apr 1, 2011 at 11:47 AM, Andres Salomon <dilinger@queued.net> wrote:
    > On Fri, 1 Apr 2011 13:20:31 +0200
    > Samuel Ortiz <sameo@linux.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.

    g.

    >
    > Can you please provide pointers to what you're referring to?  The only
    > code that I could find that created platform devices prefixed with
    > 'timb-' or named 'xilinx_spi' was drivers/mfd/timberdale.c.
    >
    >
    >
    >> To fix that problem I propose 2 alternatives:
    >>
    >> 1) When declaring the sub devices cells, the MFD driver should
    >> specify an mfd_data_size value for sub devices that are not MFD
    >> specific. It's the MFD driver responsibility to set the cell
    >> properly, and the non MFD specific drivers are kept MFD agnostic.
    >> See my patch below for the timberdale case.

    This approach worries me because it changes the behaviour on a
    per-device basis. That could be difficult to maintain a mental model
    for. I'd rather see consistent behaviour.

    >>
    >> 2) Revert the mfd_get_data() call for getting sub devices platform
    >> data pointers. That was introduced to ease the MFD cell sharing work,
    >> so if we take this route we'll need the cs5535 MFD driver to pass its
    >> cells as platform_data pointer. Andres, can you confirm that this
    >> would be fine for the mfd_clone_cell() routine to keep working ?
    >
    > It would break mfd_clone_cell, as it uses mfd_get_cell to grab the one
    > to clone.  We could change it to accept the cell as an argument.  It
    > would also break mfd_cell_enable/disable, of course.
    >
    >
    >
    >>
    >> Patch for solution 1:
    >>
    >>
    >>  drivers/mfd/mfd-core.c          |   13 ++++++++++---
    >>  drivers/mfd/timberdale.c        |   11 +++++++++++
    >>  include/linux/mfd/core.h        |    1 +
    >>  drivers/i2c/busses/i2c-ocores.c |    3 +--
    >>  drivers/i2c/busses/i2c-xiic.c   |    3 +--
    >>  drivers/net/ks8842.c            |    3 +--
    >>  drivers/spi/xilinx_spi.c        |    3 +--
    >>  7 files changed, 26 insertions(+), 11 deletions(-)
    >>
    >> diff --git a/drivers/mfd/mfd-core.c b/drivers/mfd/mfd-core.c
    >> index d01574d..8abe510 100644
    >> --- a/drivers/mfd/mfd-core.c
    >> +++ b/drivers/mfd/mfd-core.c
    >> @@ -75,9 +75,16 @@ static int mfd_add_device(struct device *parent,
    >> int id,
    >>       pdev->dev.parent = parent;
    >>
    >> -     ret = platform_device_add_data(pdev, cell, sizeof(*cell));
    >> -     if (ret)
    >> -             goto fail_res;
    >> +     if (cell->mfd_data_size > 0) {
    >> +             ret = platform_device_add_data(pdev,
    >> +                                     cell->mfd_data,
    >> cell->mfd_data_size);
    >> +             if (ret)
    >> +                     goto fail_res;
    >> +     } else {
    >> +             ret = platform_device_add_data(pdev, cell,
    >> sizeof(*cell));
    >> +             if (ret)
    >> +                     goto fail_res;
    >> +     }
    >>
    >>       for (r = 0; r < cell->num_resources; r++) {
    >>               res[r].name = cell->resources[r].name;
    >



    --
    Grant Likely, B.Sc., P.Eng.
    Secret Lab Technologies Ltd.
    --
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