• Linus Walleij's avatar
    drivers/pinctrl: grab default handles from device core · ab78029e
    Linus Walleij authored
    This makes the device core auto-grab the pinctrl handle and set
    the "default" (PINCTRL_STATE_DEFAULT) state for every device
    that is present in the device model right before probe. This will
    account for the lion's share of embedded silicon devcies.
    A modification of the semantics for pinctrl_get() is also done:
    previously if the pinctrl handle for a certain device was already
    taken, the pinctrl core would return an error. Now, since the
    core may have already default-grabbed the handle and set its
    state to "default", if the handle was already taken, this will
    be disregarded and the located, previously instanitated handle
    will be returned to the caller.
    This way all code in drivers explicitly requesting their pinctrl
    handlers will still be functional, and drivers that want to
    explicitly retrieve and switch their handles can still do that.
    But if the desired functionality is just boilerplate of this
    type in the probe() function:
    struct pinctrl  *p;
    p = devm_pinctrl_get_select_default(&dev);
    if (IS_ERR(p)) {
       if (PTR_ERR(p) == -EPROBE_DEFER)
            return -EPROBE_DEFER;
            dev_warn(&dev, "no pinctrl handle\n");
    The discussion began with the addition of such boilerplate
    to the omap4 keypad driver:
    A previous approach using notifiers was discussed:
    This failed because it could not handle deferred probes.
    This patch alone does not solve the entire dilemma faced:
    whether code should be distributed into the drivers or
    if it should be centralized to e.g. a PM domain. But it
    solves the immediate issue of the addition of boilerplate
    to a lot of drivers that just want to grab the default
    state. As mentioned, they can later explicitly retrieve
    the handle and set different states, and this could as
    well be done by e.g. PM domains as it is only related
    to a certain struct device * pointer.
    ChangeLog v4->v5 (Stephen):
    - Simplified the devicecore grab code.
    - Deleted a piece of documentation recommending that pins
      be mapped to a device rather than hogged.
    ChangeLog v3->v4 (Linus):
    - Drop overzealous NULL checks.
    - Move kref initialization to pinctrl_create().
    - Seeking Tested-by from Stephen Warren so we do not disturb
      the Tegra platform.
    - Seeking ACK on this from Greg (and others who like it) so I
      can merge it through the pinctrl subsystem.
    ChangeLog v2->v3 (Linus):
    - Abstain from using IS_ERR_OR_NULL() in the driver core,
      Russell recently sent a patch to remove it. Handle the
      NULL case explicitly even though it's a bogus case.
    - Make sure we handle probe deferral correctly in the device
      core file. devm_kfree() the container on error so we don't
      waste memory for devices without pinctrl handles.
    - Introduce reference counting into the pinctrl core using
      <linux/kref.h> so that we don't release pinctrl handles
      that have been obtained for two or more places.
    ChangeLog v1->v2 (Linus):
    - Only store a pointer in the device struct, and only allocate
      this if it's really used by the device.
    Cc: Felipe Balbi <balbi@ti.com>
    Cc: Benoit Cousson <b-cousson@ti.com>
    Cc: Dmitry Torokhov <dmitry.torokhov@gmail.com>
    Cc: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
    Cc: Mitch Bradley <wmb@firmworks.com>
    Cc: Ulf Hansson <ulf.hansson@linaro.org>
    Cc: Rafael J. Wysocki <rjw@sisk.pl>
    Cc: Jean-Christophe PLAGNIOL-VILLARD <plagnioj@jcrosoft.com>
    Cc: Rickard Andersson <rickard.andersson@stericsson.com>
    Cc: Russell King <linux@arm.linux.org.uk>
    Reviewed-by: default avatarMark Brown <broonie@opensource.wolfsonmicro.com>
    Acked-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
    Signed-off-by: default avatarLinus Walleij <linus.walleij@linaro.org>
    [swarren: fixed and simplified error-handling in pinctrl_bind_pins(), to
    correctly handle deferred probe. Removed admonition from docs not to use
    pinctrl hogs for devices]
    Signed-off-by: default avatarStephen Warren <swarren@nvidia.com>
    Signed-off-by: default avatarLinus Walleij <linus.walleij@linaro.org>
pinctrl.c 1.62 KB