topic Re: How to Enable Gated Clock for GPT in Linux User Space Driver in i.MX Processors

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

brianyokum — Mon, 02 Jul 2018 23:48:55 GMT

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?

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

igorpadykov — Tue, 10 Jul 2018 11:17:31 GMT

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

brianyokum — Tue, 10 Jul 2018 15:27:26 GMT

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.