Re: DVS regulator drivers

Guennadi Liakhovetski
2012-11-20T08:17:50Z

Hi Mark

Thanks for your reply.

On Tue, 20 Nov 2012, Mark Brown wrote:

> On Mon, Nov 19, 2012 at 12:52:09PM +0100, Guennadi Liakhovetski wrote:
> > As I mentioned in an earlier mail today [1] I have a difficulty seeing how
> > the current regulator API can efficiently be used for DVS-type regulators.
>
> Please don't invent terminology or repurpose existing terminology like
> this, it's just confusing - obvious essentially all regulators covered
> by the regulator API support voltage scaling which is the usual meaning
> of DVS.

Right, sorry, a more precise term would be a "pin-selectable DVS," right?

> > wm831x-dcdc.c handles 2 voltages: "DVS" and "ON." If the new voltage in
> > .set_voltage_sel() is equal to one of them, it is just used. If it is a
> > new voltage, there's a comment in the driver in
> > wm831x_buckv_set_voltage_sel():
>
> > /* Always set the ON status to the minimum voltage */
>
> > but I actually don't see, where the minimum is selected. It seems instead
> > in this case the "ON" value is just set:
>
> > ret = wm831x_set_bits(wm831x, on_reg, WM831X_DC1_ON_VSEL_MASK, vsel);
> > if (ret < 0)
> > return ret;
> > dcdc->on_vsel = vsel;
>
> Can you be more specific about your concern here? The above code does
> exactly what the comment says, it will set the selector it just picked.

Your patch fixes exactly the problem, that I was pointing at, thanks.

> You did spot one bug (I think due to bitrot) which I just fixed but in
> general I've just TLDRed this as it's a bit unclear what you're trying
> to say here, can you be a bit more concise here? I'm not sure if
> there's a general point or if it's specific code issues?

Sorry, let's try again. Just to bring back the "too long and a bit unclear
part:"

> > lp872x.c seems to be selecting between ON and DVS (or V1 and V2 in lp872x'
> > terminology) in lp872x_set_dvs(), which is called every time a voltage is
> > set. But this function always gets the same arguments - supplied from the
> > platform data and therefore only one voltage is ever used... The two
> > "dynamic" DVS selection fields in struct lp872x: .dvs_pin and .dvs_gpio
> > seem just to always stay constant, the latter is also just initialised
> > once and is never used again.

Ok, what I meant is the following:

1. some fields of struct lp872x are superfluous / unused, e.g. .dvs_gpio
is only set once and never used again, .dvs_pin seems to be used, but I
think it's never changed either, because:

2. .dvs_pin is initialised in lp872x_init_dvs() from platform data:

pinstate = dvs->init_state;
...
lp->dvs_pin = pinstate;

There's one more location in the code, where .dvs_pin gets assigned: in
lp872x_set_dvs():

lp->dvs_pin = state;

but, I think, it will always be set to one and the same value: "state" is
calculated as

state = dvs_sel == SEL_V1 ? DVS_HIGH : DVS_LOW;

where dvs_sel is a parameter of this function. The function is called only
from one location in lp872x_buck_set_voltage_sel() as

lp872x_set_dvs(lp, dvs->vsel, dvs->gpio);

where dvs is platform data, i.e., all parameters are constant. So,
lp872x_set_dvs() never switches anything, and in fact it could just have
been called just once from initialisation to set the GPIO. This also
means, that only one context - either SEL_V1 or SEL_V2 is used.