topic Not clear if mx53 linux DVFS enabled or not in i.MX Processors

Not clear if mx53 linux DVFS enabled or not

bdp42 — Wed, 10 Jun 2015 17:48:06 GMT

I'm investigating DVFS on an IMX53 based platform running Linux. We are using the Freescale Android 10.2 BSP

Both frequency and voltage scaling appear to be enabled - as shown below:

cat /sys/devices/platform/mxc_dvfs_core.0/enable

DVFS is enabled

However when I look at the min and max frequencies I see the following

cat /sys/devices/system/cpu/cpu0/cpufreq/cpuinfo_max_freq

800000

cat /sys/devices/system/cpu/cpu0/cpufreq/cpuinfo_min_freq

800000

This suggests that only one frequency is used and so no scaling is taking place.

Is this correct? If so how can I change this?

Thanks,

Bruno

Re: Not clear if mx53 linux DVFS enabled or not

igorpadykov — Thu, 11 Jun 2015 02:37:29 GMT

Hi Bruno

sect.20.2 Software Operation attached document

shows how to enable DVFS.

Best regards

igor

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Re: Not clear if mx53 linux DVFS enabled or not

bdp42 — Thu, 11 Jun 2015 08:10:32 GMT

Hi Igor,

I have seen this and DVFS is enabled as described in the document.

However the issue is that the min and max frequencies as shown by the proc file system are the same which suggests no frequency scaling can take place.

The min and max values seem to derive from a table in the file kernel_imx/arch/arm/mach-mx5/mx53_wp.c. There are a number of structures ( dvfs_wp and cpu_wp ) that seem to have a bearing on this but I have not been able to find a description of their usage. I've included the relevant ones that are being used for our board.

/* Place holder for dvfs_core setpoints for AEC parts */

static struct dvfs_wp dvfs_core_setpoint_aec[] = {

{33, 0, 33, 10, 10, 0x08} }; /*800MHz*/

/* working point for auto */

static struct cpu_wp cpu_wp_aec[] = {

{

.pll_rate = 800000000,

.cpu_rate = 800000000,

.pdf = 0,

.mfi = 8,

.mfd = 2,

.mfn = 1,

.cpu_podf = 0,

.cpu_voltage = 1100000,},

};

So can frequency scaling take place if the min and max frequency are the same? Is this determined by the structures shown above and, if so, how should these structures be used?

Thanks,

Bruno

Re: Not clear if mx53 linux DVFS enabled or not

igorpadykov — Thu, 11 Jun 2015 09:15:12 GMT

Hi Bruno

had board followed i.MX53 SMD design and has PMIC ?

Also could you try with linux

L2.6.35_11.05_ER_SOURCE : Linux 2.6.35 Source Code Files

and documentation 11.05 for i.MX53 SABRE Tablet.

~igor

Re: Not clear if mx53 linux DVFS enabled or not

bdp42 — Fri, 12 Jun 2015 10:26:53 GMT

Hi Igor,

We have followed the mx53_ard design and we do have a PMIC (LTC3589) . Is there something different in the mx53_smd design regarding DVFS that we should be following?

Thanks,

Bruno

Re: Not clear if mx53 linux DVFS enabled or not

igorpadykov — Fri, 12 Jun 2015 11:09:24 GMT

Hi Bruno

Automotive IMX53AEC option has only one

operating point (working point defined in arch/arm/mach-mx5/mx53_wp.c) 800MHz

opposite to consumer IMX53CEC

so one can consider that automotive has not DVFS mode

~igor

Re: Not clear if mx53 linux DVFS enabled or not

bdp42 — Mon, 15 Jun 2015 09:00:40 GMT

Hi Igor,

But is there any reason why we can't use frequencies lower than 800MHz?

Thanks,

Bruno

Re: Not clear if mx53 linux DVFS enabled or not

igorpadykov — Mon, 15 Jun 2015 09:06:30 GMT

Hi Bruno

automotive parts were not characterized for these

frequencies.

~igor

Re: Not clear if mx53 linux DVFS enabled or not

bdp42 — Mon, 15 Jun 2015 16:49:34 GMT

Hi Igor,

800Mz. is the maximum frequency of the AEC part. So it can run at lower frequencies. It just hasn't been characterised at these lower frequencies. Is this correct?

Bruno

Re: Not clear if mx53 linux DVFS enabled or not

igorpadykov — Tue, 16 Jun 2015 02:06:35 GMT

Hi Bruno

it can at lower frequencies without changing

core voltage. It hasn't been characterised for operation with lower

core voltages running at lower frequencies.

~igor