Hi Eric,
On Mon, Jan 14, 2013 at 08:43:35AM -0700, Eric Nelson wrote:
> >+ /* scaling up? scale voltage before frequency */
> >+ if (freqs.new > freqs.old) {
> >+ ret = regulator_set_voltage_tol(arm_reg, volt, 0);
> >+ if (ret) {
> >+ dev_err(cpu_dev, "failed to scale voltage up: %d\n", ret);
> >+ return ret;
> >+ }
> >+
> >+ /*
> >+ * Need to increase vddpu and vddsoc for safety
> >+ * if we are about to run at 1.2 GHz.
> >+ */
> >+ if (freqs.new == FREQ_1P2_GHZ / 1000) {
> >+ regulator_set_voltage_tol(pu_reg,
> >+ PU_SOC_VOLTAGE_HIGH, 0);
> >+ regulator_set_voltage_tol(soc_reg,
> >+ PU_SOC_VOLTAGE_HIGH, 0);
> >+ }
>
> I believe you need a delay here to let the LDOs ramp before changing
> the CPU frequency.
>
> According to the i.MX6Q reference manual, with the factory default
> step times in PMU_MISC2 and the maximum voltage swing is
> 1.25V (1.2GHz) - 0.95V (400MHz) == 0.325V
>
> or 13 steps at 25mV.
>
> The default step time is 0.000021333s (512 clocks at 24MHz), so
> the worst case delay needed is ~280uS.
>
> This could also be done in the regulator driver, but that may
> require multiple delays if multiple rails are changed.
>
I initially thought that regulator driver should take care of it. But
now I agree with you that we can do it here for the least latency.
Will roll it into v4. Thanks.
Shawn
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