• eric miao's avatar
    [ARM] pxa: add MFP-alike pin configuration support for pxa{25x, 27x} · 7facc2f9
    eric miao authored
    Pin configuration on pxa{25x,27x} has now separated from generic GPIO
    into dedicated mfp-pxa2xx.c by this patch. The name "mfp" is borrowed
    from pxa3xx and is used here to alert the difference between the two
    concepts: pin configuration and generic GPIOs.  A GPIO can be called
    a "GPIO" _only_ when the corresponding pin is configured so.
    
    A pin configuration on pxa{25x,27x} is composed of:
    
        - alternate function selection (or pin mux as commonly called)
        - low power state or sleep state
        - wakeup enabling from low power mode
    
    The following MFP_xxx bit definitions in mfp.h are re-used:
    
        - MFP_PIN(x)
        - MFP_AFx
        - MFP_LPM_DRIVE_{LOW, HIGH}
        - MFP_LPM_EDGE_*
    
    Selecting alternate function on pxa{25x, 27x} involves configuration
    of GPIO direction register GPDRx, so a new bit and MFP_DIR_{IN, OUT}
    are introduced. And pin configurations are defined by the following
    two macros:
    
        - MFP_CFG_IN  : for input alternate functions
        - MFP_CFG_OUT : for output alternate functions
    
    Every configuration should provide a low power state if it configured
    as output using MFP_CFG_OUT().  As a general guideline, the low power
    state should be decided to minimize the overall power dissipation. As
    an example, it is better to drive the pin as high level in low power
    mode if the GPIO is configured as an active low chip select.
    
    Pins configured as GPIO are defined by MFP_CFG_IN(). This is to avoid
    side effects when it is firstly configured as output.  The actual
    direction of the GPIO is configured by gpio_direction_{input, output}
    
    Wakeup enabling on pxa{25x, 27x} is actually GPIO based wakeup, thus
    the device based enable_irq_wake() mechanism is not applicable here.
    
    E.g.  invoking enable_irq_wake() with a GPIO IRQ as in the following
    code to enable OTG wakeup is by no means portable and intuitive, and
    it is valid _only_ when GPIO35 is configured as USB_P2_1:
    
        enable_irq_wake( gpio_to_irq(35) );
    
    To make things worse, not every GPIO is able to wakeup the system.
    Only a small number of them can, on either rising or falling edge,
    or when level is high (for keypad GPIOs).
    
    Thus, another new bit is introduced to indicate that the GPIO will
    wakeup the system:
    
        - MFP_LPM_WAKEUP_ENABLE
    
    The following macros can be used in platform code, and be OR'ed to
    the GPIO configuration to enable its wakeup:
    
        - WAKEUP_ON_EDGE_{RISE, FALL, BOTH}
        - WAKEUP_ON_LEVEL_HIGH
    
    The WAKEUP_ON_LEVEL_HIGH is used for keypad GPIOs _only_, there is
    no edge settings for those GPIOs.
    
    These WAKEUP_ON_* flags OR'ed on wrong GPIOs will be ignored in case
    that platform code author is careless enough.
    
    The tradeoff here is that the wakeup source is fully determined by
    the platform configuration, instead of enable_irq_wake().
    Signed-off-by: default avatareric miao <eric.miao@marvell.com>
    Signed-off-by: default avatarRussell King <rmk+kernel@arm.linux.org.uk>
    7facc2f9
mfp-pxa2xx.c 3.96 KB