How to Enable Gated Clock for GPT in Linux User Space Driver

[brianyokum]

I am trying to implement a Linux user space driver for the GPT on the i.MX6ULL using uio_pdrv_genirq.  I have the basic driver set up, but the system locks up when I try to access the GPT registers.  I saw this same problem when I originally implemented the driver as a kernel space driver.  It was caused by the gated clock for the GPT not being enabled.  Is there a way to enable the needed clocks in the user space driver?  Is there a way to enable the clock outside the driver, perhaps through a device tree setting?  Is there a change to clk-imx6ul.c or another file that can accomplish this?

[brianyokum]

Igor,

It appears that Linux uses GPT1 for the system timer.  GPT2 is normally disabled in the device tree, and it appears that it is available for use.

The U-Boot configuration enables all the clocks during boot, but the Linux kernel shuts down unused clocks once it starts.  I was looking for something similar to clk_prepare_enable() that can be called from user space.

[igorpadykov]

Hi Brian

gpt can be used by linux as system timer according to sect.3.3 Timer

attached Linux Manual. Module clocks can be enabled in uboot/board/freescale/mx6ullevk/imximage.cfg

uboot-imx.git - Freescale i.MX u-boot Tree 

Best regards
igor
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