How to change clock source for GPTIMERs in Linux driver?

So this is the code in the probe function of my PWM driver that tries to change the clock source to the sys_clk.

        pwm_data[i].clk_fck = clk_get(&pdev->dev, clk_fck_id[i]);     // i=0 and clk_fck_id[0] = "gpt10_fck"
        if ( IS_ERR(pwm_data[i].clk_fck)) {
            ret = PTR_ERR(pwm_data[i].clk_fck);
            goto probe_exit;
        }
        
        ret = clk_enable(pwm_data[i].clk_fck);
        if(ret)
        {
            dev_err(&pdev->dev, "Unable to start clk_fck%d, %d\n", i, ret);
            goto probe_exit;
        }

        sys_ck = clk_get(&pdev->dev, "sys_ck");
        if ( IS_ERR(sys_ck) ) {
            ret = PTR_ERR(sys_ck);
            goto probe_exit;
        }
        rate = clk_get_rate(pwm_data[i].clk_fck);
        printk("PWM%d init, sys_ck: %dHz\n", i, rate);

        ret = clk_set_rate(pwm_data[i].clk_fck, rate);
        if(ret)
        {
            dev_err(&pdev->dev, "Unable to set clk rate clk_fck%d, %d\n", i, ret);
            goto probe_exit;
        }

And I get the following error when booting Linux, an "-EINVAL" from the omap2_clk_set_rate function.

[    1.680328] at24 1-0050: 16384 byte 24c128 EEPROM (writable)
[    1.686920] omap_device: omap_i2c.1: new worst case activate latency 0: 91552
[    1.695404] Read MAC addr from EEPROM: 02:05:7d:04:01:50
[    1.702423] PWM0 init, sys_ck: 13000000Hz
[    1.706726] clock: set_rate for clock gpt10_fck to rate 13000000
[    1.712982] r5cdupwm r5cdupwm.0: Unable to set clk rate clk_fck0, -22
[    1.719818] r5cdupwm: probe of r5cdupwm.0 failed with error -22
[    1.729949] R5 CDU LED dirver initialized successfully

There are no set_rate() functions defined for the GPTIMERs in clock3xxx_data.c.
Is this the wrong way of doing it, using the clk_set_rate() function, is there any other way?

Regards,
Anders

Hi Kevin

Sorry for not responding to your message.

The driver I wrote that include a PWM driver is not that general so maybe that's not the best example code.

But you can take a look at this page http://elinux.org/BeagleBoard/GSoC/2010_Projects/Pulse_Width_Modulation it's a PWM driver for BeagleBoard and the OMAP3 which has the same PWM circuit as the AM3517. It is the code that I used as an example when writing my driver. Take a look at the code and if you have any questions, feel free to ask.

//Anders

Hello,

Here's another fine tutorial about using OMAP general-purpose hardware timers: I sucessfully compiled and ran it on the AM3517 processor.  As for clock source control, I selected system clock as the source for all the timers my app requests, then 'go with the flow'. The timer driver just enquires about its freqency and live with that. Mine is about 6.5 MHz, which is fine for me because I use the timer to trigger events every 50 ms.

http://www.kunen.org/uC/beagle/omap_dmtimer.html