Siege lion parsing for registration and Shu clock use of (a)

When we write or modify driving, often encounter problems related to the clock, I do not know where to start. Herein, in the version 3.0.35 kernel i.MX6 example how to obtain and use the clock.

The most common way to get the clock
❶ acquisition by name
, for example: Get clock clko

clko = clk_get(NULL, "clko_clk");

❷ acquired by the apparatus
, for example, the driving clock is eligible ssi's audio interface,

ssi-> clk = clk_get (& pdev-> dev, NULL); // device name is "imx-ssi"

We can always check how is obtained by looking at the function prototype of clk_get

struct clk clk_get(struct device dev, const char *con_id)

{

    const char *dev_id = dev ? dev_name(dev) : NULL;

     return clk_get_sys(dev_id, con_id);

}

We continue to view the function clk_get_sys, this function to get the clock by equipment name or the name of the clock

struct clk clk_get_sys(const char dev_id, const char *con_id)

{

     struct clk_lookup *cl;

     mutex_lock(&clocks_mutex); 

     cl = clk_find(dev_id, con_id);

     if (cl && !__clk_get(cl->clk))

             cl = NULL;

     mutex_unlock(&clocks_mutex);

     return cl ? cl->clk : ERR_PTR(-ENOENT);

}

This function calls clk_find get the clock to find according to the device name and the name of the clock in the clock list, and return to get the clock.

static struct clk_lookup clk_find(const char dev_id, const char *con_id)

{

     struct clk_lookup *p, *cl = NULL;

     int match, best = 0;

     list_for_each_entry(p, &clocks, node) {

             match = 0;

             if (p->dev_id) {

                     if (!dev_id || strcmp(p->dev_id,dev_id))

                             continue;

                     match += 2;

             } // 先找设备名

             if (p->con_id) {//再找时钟名

                     if (!con_id || strcmp(p->con_id,con_id))

                             continue;

                     match += 1;

             }

             if (match > best) {

                     cl = p;

                     if (match != 3)

                             best=match;

                     else

                             break;

             }

     }

     return cl;}

Registration clock
mentioned the acquisition clock, the clock from the list within a list according to the clock or clock device name is how generated.

We call the clock initialization function in i.Mx6 board-level initialization file inside.

static void __init mx6_sabresd_timer_init(void)

{

     struct clk *uart_clk;

#ifdef CONFIG_LOCAL_TIMERS

     twd_base = ioremap(LOCAL_TWD_ADDR,SZ_256);

     BUG_ON(!twd_base);

#endif

     mx6_clocks_init(32768, 24000000, 0, 0);

     uart_clk = clk_get_sys("imx-uart.0", NULL);

     early_console_setup(UART1_BASE_ADDR, uart_clk);

}

We see mx6_clocks_init function

int __init mx6_clocks_init(unsigned long ckil, unsigned long osc,

     unsigned long ckih1, unsigned long ckih2)

{

    …

     for (i = 0; i < ARRAY_SIZE(lookups); i++）{

             clkdev_add(&lookups[i]);

             clk_debug_register(lookups[i].clk);

     }

….

}

Inside look at the array of function lookups decided how many clock

static struct clk_lookup lookups[] = {

 ……

_REGISTER_CLOCK("imx-ssi.0", NULL, ssi1_clk),

     _REGISTER_CLOCK("imx-ssi.1", NULL, ssi2_clk),

     _REGISTER_CLOCK("imx-ssi.2", NULL, ssi3_clk),

_REGISTER_CLOCK(NULL, "clko_clk", clko_clk),

……

}

clk_lookup definition

struct clk_lookup {

     struct list_head          node;

     const char                *dev_id;

     const char                *con_id;

     struct clk                *clk;

};

clk_lookup assignment

#define _REGISTER_CLOCK(d, n, c) \

     { \

             .dev_id = d, \

             .con_id = n, \

             .clk = &c, \

     }

Look function clkdev_add

void clkdev_add(struct clk_lookup *cl){

     mutex_lock(&clocks_mutex);

     list_add_tail(&cl->node, &clocks);

     mutex_unlock(&clocks_mutex);

}

Thus, we can find mx6_clocks_init clock function in the array lookups, all added to the list within clocks. We then get the clock defined by the first step in the lookups method.