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SubjectRe: [PATCH 6/8] PM / OPP: Support adjusting OPP voltages at runtime
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Dear Stephen Boyd,

This patch is derived from [1]. Please kindly shares the suggestion to
us. Thanks very much.

[1]: https://lore.kernel.org/patchwork/patch/599279/

Dear Viresh,

I followed _opp_set_availability() coding style to refine
dev_pm_opp_adjust_voltage() from this patch. Is this refinement suitable
for OPP core? Thanks a lot.

On Mon, 2019-05-20 at 12:47 +0800, Viresh Kumar wrote:
> On 16-05-19, 17:08, Andrew-sh.Cheng wrote:
> > From: Stephen Boyd <sboyd@codeaurora.org>
> >
> > On some SoCs the Adaptive Voltage Scaling (AVS) technique is
> > employed to optimize the operating voltage of a device. At a
> > given frequency, the hardware monitors dynamic factors and either
> > makes a suggestion for how much to adjust a voltage for the
> > current frequency, or it automatically adjusts the voltage
> > without software intervention. Add an API to the OPP library for
> > the former case, so that AVS type devices can update the voltages
> > for an OPP when the hardware determines the voltage should
> > change. The assumption is that drivers like CPUfreq or devfreq
> > will register for the OPP notifiers and adjust the voltage
> > according to suggestions that AVS makes.
> >
> > This patch is devired from [1] submitted by Stephen.
> > [1] https://lore.kernel.org/patchwork/patch/599279/
> >
> > Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>
> > Signed-off-by: Roger Lu <roger.lu@mediatek.com>
> > ---
> > drivers/opp/core.c | 78 ++++++++++++++++++++++++++++++++++++++++++++++++++
> > include/linux/pm_opp.h | 11 +++++++
> > 2 files changed, 89 insertions(+)
>
> This is an rcu implementation which got removed long back from OPP core. Please
> align this with the latest changes.
>


/**
* dev_pm_opp_adjust_voltage() - helper to change the voltage of an OPP
* @dev: device for which we do this operation
* @freq: OPP frequency to adjust voltage of
* @u_volt: new OPP voltage
*
* Return: -EINVAL for bad pointers, -ENOMEM if no memory available for
the
* copy operation, returns 0 if no modifcation was done OR modification
was
* successful.
*/
int dev_pm_opp_adjust_voltage(struct device *dev, unsigned long freq,
unsigned long u_volt)
{
struct opp_table *opp_table;
struct dev_pm_opp *tmp_opp, *opp = ERR_PTR(-ENODEV);
int r = 0;

/* Find the opp_table */
opp_table = _find_opp_table(dev);
if (IS_ERR(opp_table)) {
r = PTR_ERR(opp_table);
dev_warn(dev, "%s: Device OPP not found (%d)\n", __func__, r);
return r;
}

mutex_lock(&opp_table->lock);

/* Do we have the frequency? */
list_for_each_entry(tmp_opp, &opp_table->opp_list, node) {
if (tmp_opp->rate == freq) {
opp = tmp_opp;
break;
}
}

if (IS_ERR(opp)) {
r = PTR_ERR(opp);
goto adjust_unlock;
}

/* Is update really needed? */
if (opp->supplies->u_volt == u_volt)
goto adjust_unlock;

opp->supplies->u_volt = u_volt;

dev_pm_opp_get(opp);
mutex_unlock(&opp_table->lock);

/* Notify the voltage change of the OPP */
blocking_notifier_call_chain(&opp_table->head,
OPP_EVENT_ADJUST_VOLTAGE,
opp);

dev_pm_opp_put(opp);
goto adjust_put_table;

adjust_unlock:
mutex_unlock(&opp_table->lock);
adjust_put_table:
dev_pm_opp_put_opp_table(opp_table);
return r;
}

Sincerely,
Roger Lu.

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