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    SubjectRe: [PATCH 7/7] OF/ACPI/I2C: Add generic match function for the aforementioned systems
    On Wed, 04 Jun 2014, Mika Westerberg wrote:
    > On Wed, Jun 04, 2014 at 02:37:42PM +0200, Rafael J. Wysocki wrote:
    > > On Wednesday, June 04, 2014 01:09:56 PM Lee Jones wrote:
    > > > Currently this is a helper function for the I2C subsystem to aid the
    > > > matching of non-standard compatible strings and devices which use DT
    > > > and/or ACPI, but do not supply any nodes (see: [1] Method 4). However,
    > > > it has been made more generic as it can be used to only make one call
    > > > for drivers which support any mixture of OF, ACPI and/or I2C matching.
    > > >
    > > > The initial aim is for of_match_device() to be replaced by this call
    > > > in all I2C device drivers.
    > > >
    > > > [1] Documentation/i2c/instantiating-devices
    > > >
    > > > Signed-off-by: Lee Jones <lee.jones@linaro.org>
    > >
    > > Mika, can you please have a look at this, please?
    >
    > I don't see any fundamental problems with this wrt. ACPI.
    >
    > That said, I find it kind of weird to have generic function that then
    > has knowledge of how different buses do their matching.
    >
    > I would rather see something like firmware_device_match(dev) that goes
    > and matches from DT/ACPI and leave bus specific match to happen internal
    > to that bus.

    Unfortunately that completely defeats the object of the patch. When a
    of_match_device() is invoked it solely looks up devices based on OF
    matching, but I2C is special in that devices can be registered via
    sysfs, thus will no have device node. If of_match_device() is called
    in one of these instances it will fail. The idea of this patch is to
    generify the matching into something does has the knowledge to firstly
    attempt a traditional match, and if that fails will fall back to a
    special i2c_{of,acpi}_match_device() which knows how to deal with
    node-less registration.

    We don't support that for ACPI yet, as I don't have a system to test
    it on, but when we do acpi_match_device() in the patch will too be
    swapped out for an equivalent i2c_acpi_match_device().

    Actually, I've just spotted that this patch is wrong I need to change
    it in the following way:

    > > > ---
    > > > include/linux/match.h | 40 ++++++++++++++++++++++++++++++++++++++++
    > > > 1 file changed, 40 insertions(+)
    > > > create mode 100644 include/linux/match.h
    > > >
    > > > diff --git a/include/linux/match.h b/include/linux/match.h
    > > > new file mode 100644
    > > > index 0000000..20a08e2
    > > > --- /dev/null
    > > > +++ b/include/linux/match.h
    > > > @@ -0,0 +1,40 @@
    > > > +#include <linux/of.h>
    > > > +#include <linux/acpi.h>
    > > > +#include <linux/i2c.h>
    > > > +
    > > > +static void *device_match(struct device *dev)
    > > > +{
    > > > + struct device_driver *driver = dev->driver;
    > > > +
    > > > + if (!driver)
    > > > + return NULL;
    > > > +
    > > > + /* Attempt an OF style match */
    > > > + if (IS_ENABLED(CONFIG_OF)) {
    > > > + const struct of_device_id *of_match =
    > > > + i2c_of_match_device(driver->of_match_table, dev);
    This should be of_match_device()

    > > > + if (of_match)
    > > > + return (void *)of_match;
    > > > + }
    > > > +
    > > > + /* Then ACPI style match */
    > > > + if (IS_ENABLED(CONFIG_ACPI)) {
    > > > + const struct acpi_device_id *acpi_match =
    > > > + acpi_match_device(driver->acpi_match_table, dev);
    > > > + if (acpi_match)
    > > > + return (void *)acpi_match;
    > > > + }
    > > > +
    > > > + /* Finally an I2C match */
    > > > + if (IS_ENABLED(CONFIG_I2C)) {
    > > > + struct i2c_client *client = i2c_verify_client(dev);
    > > > + struct i2c_driver *i2c_drv = to_i2c_driver(driver);
    > > > + struct i2c_device_id *i2c_match;

    i2c_of_match_device() and later i2c_acpi_match_device() should be here.

    > > > + i2c_match = i2c_match_id(i2c_drv->id_table, client);
    > > > + if (i2c_match)
    > > > + return (void *)i2c_match;
    > > > + }
    > > > +
    > > > + return NULL;
    > > > +}
    > > >
    > >

    --
    Lee Jones
    Linaro STMicroelectronics Landing Team Lead
    Linaro.org │ Open source software for ARM SoCs
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