What is the impact of MLK-13801-02 ARM: dts: Correct the gpt timer clock source on imx6ul/ull/sll

[shaot]

Hi, I use imx6ull and Yocto.

The past product uses imx6ull.dtsi before this commit.

MLK-13801-02 ARM: dts: Correct the gpt timer clock source on imx6ul/ull/sll

The GPT timer counter clock should be sourced from GPT_3M clock to avoid
counter clock frequency changed due to system bus clock changes.

Signed-off-by: Bai Ping <ping.bai@nxp.com>
(cherry picked from commit 3f85257a0ab3471f2574d5a34a311d4ef4483f7d)

https://github.com/varigit/linux-2.6-imx/commit/41aad2ae5da3fe1212ef833481d90796b43b2687#diff-93407b...

1. What will occur if we do not change to IMX6UL_CLK_GPT_3M ? System hangs? If so, when or what condition causes this?

2. What is GPT timer counter used for ? Linux Kernel uses it?

Best regards

[shaot]

From this https://community.nxp.com/t5/i-MX-Processors/iMX6-GPT-linux-kernel-3-0-35/td-p/241982,

it seems Linux Kernel uses GPT. Is it right?

Would you tell me what is the concern if we do not change to IMX6UL_CLK_GPT_3M ?

Best regards 

[joanxie]

Original gpt per clk parent is from ipg_per clk which may be scaled when system enter low bus mode, as ipg clk will be lower in low bus mode, to keep system clk NOT drift, select gpt per clk parent from OSC which is at fixed freq always

[joanxie]

this patch is already included in the latest bsp, why don't you apply this? don't you  want to use this patch?

[shaot]

I know it.

The product which is not applied this patch was already shipped.

So I would like to understand the influence of this change.

[shaot]

Thank you.

Does "low bus mode" mean low frequency mode?

Our products work in fixed 900MHz (max frequency), so it does not affect anything?

[joanxie · Accepted solution]

900M should be ok, you can see the detailed information from the source code as below:

 on i.MX6ULL, when entering low bus mode, the ARM core
 * can run at 24MHz to support the low power run mode per
 * to design team.

"https://source.codeaurora.org/external/imx/linux-imx/tree/arch/arm/mach-imx/busfreq-imx.c?h=imx_4.14..."

[shaot]

Thank you. I understand the influence.