[alsa-devel] [PATCH] ASoC: Add device tree binding for WM8753

[Barry Song]

2011/8/9 Mark Brown <broonie at opensource.wolfsonmicro.com>:
> On Mon, Aug 08, 2011 at 11:51:00PM -0700, Dmitry Torokhov wrote:
>
>> The issue I have with the ads7846 driver is that it still needs platform
>> code to supply the needed platform data structure to make the
>> driver/device usable. So I am not sure what the benefit DT matching code
>> brings to that driver.
>
> Oh, if that's the case the driver ought to have device tree bindings
> which replicate the platform data.  Unless the platform data is
> sufficiently obscure for hardly anyone to want to use it I guess.
>
With the device tree binding in ads7846, we don't need spi_board_info
any more since we have
ts at 0 {
       compatible = "ti,ads7845";
       reg = <0x0>;
       spi-max-frequency = <31250>;
       interrupts = <90>;
};
in dts.

I guess what Dmitry said is the big ads7846_platform_data structure.

 struct ads7846_platform_data {
        u16     model;                  /* 7843, 7845, 7846, 7873. */
        u16     vref_delay_usecs;       /* 0 for external vref; etc */
        u16     vref_mv;                /* external vref value, milliVolts
                                         * ads7846: if 0, use internal vref */
        bool    keep_vref_on;           /* set to keep vref on for differential
                                         * measurements as well */
        bool    swap_xy;                /* swap x and y axes */

        /* Settling time of the analog signals; a function of Vcc and the
         * capacitance on the X/Y drivers.  If set to non-zero, two samples
         * are taken with settle_delay us apart, and the second one is used.
         * ~150 uSec with 0.01uF caps.
         */
        u16     settle_delay_usecs;

        /* If set to non-zero, after samples are taken this delay is applied
         * and penirq is rechecked, to help avoid false events.  This value
         * is affected by the material used to build the touch layer.
         */
        u16     penirq_recheck_delay_usecs;

        u16     x_plate_ohms;
        u16     y_plate_ohms;

        u16     x_min, x_max;
        u16     y_min, y_max;
        u16     pressure_min, pressure_max;

        u16     debounce_max;           /* max number of additional readings
                                         * per sample */
        u16     debounce_tol;           /* tolerance used for filtering */
        u16     debounce_rep;           /* additional consecutive good readings
                                         * required after the first two */
        int     gpio_pendown;           /* the GPIO used to decide the pendown
                                         * state if get_pendown_state == NULL
                                         */
        int     (*get_pendown_state)(void);
        int     (*filter_init)  (const struct ads7846_platform_data *pdata,
                                 void **filter_data);
        int     (*filter)       (void *filter_data, int data_idx, int *val);
        void    (*filter_cleanup)(void *filter_data);
        void    (*wait_for_sync)(void);
        bool    wakeup;
        unsigned long irq_flags;
};

The structure even has some callbacks which can't be possible in dts.