Re: [PATCH v2] backlight: lp855x: use private data for regulator control

[Kim, Milo]

Hi Paul,

On 7/11/2015 5:52 AM, Kim, Milo wrote:
> Hi Paul,
>
> On 7/11/2015 5:49 AM, Sean Paul wrote:
> > On Fri, Jul 10, 2015 at 4:43 PM, Kim, Milo <milo.kim@xxxxxx> wrote:
> > > Hi Paul,
> > >
> > >
> > > On 7/11/2015 12:01 AM, Sean Paul wrote:
> > > > On Fri, Jul 10, 2015 at 4:26 AM, Milo Kim <milo.kim@xxxxxx> wrote:
> > > > > LP855x backlight device can be enabled by external VDD input.
> > > > > The 'supply' data is used for this purpose.
> > > > > It's kind of private data which runs internally, so there is no reason to
> > > > > expose to the platform data.
> > > > >
> > > > > And devm_regulator_get() is moved from _parse_dt() to _probe().
> > > > > Regulator consumer(lp855x) can control regulator not only from DT but
> > > > > also
> > > > > from platform data configuration in a source file such like board-*.c.
> > > > >
> > > > > If 'power' regulator driver is not ready, lp855x should continue to work
> > > > > because the power supply control is optional. So -EPROBE_DEFER return
> > > > > code
> > > > > is removed.
> > > > >
> > > > > v1->v2:
> > > > >      Keeps optional property '<name>-supply' in LP855x DT binding.
> > > > >
> > > > > Cc: Sean Paul <seanpaul@xxxxxxxxxxxx>
> > > > > Cc: Jingoo Han <jingoohan1@xxxxxxxxx>
> > > > > Cc: Lee Jones <lee.jones@xxxxxxxxxx>
> > > > > Cc: linux-kernel@xxxxxxxxxxxxxxx
> > > > > Signed-off-by: Milo Kim <milo.kim@xxxxxx>
> > > > > ---
> > > > >     drivers/video/backlight/lp855x_bl.c  | 20 +++++++++-----------
> > > > >     include/linux/platform_data/lp855x.h |  2 --
> > > > >     2 files changed, 9 insertions(+), 13 deletions(-)
> > > > >
> > > > > diff --git a/drivers/video/backlight/lp855x_bl.c
> > > > > b/drivers/video/backlight/lp855x_bl.c
> > > > > index a26d3bb..277d5ca 100644
> > > > > --- a/drivers/video/backlight/lp855x_bl.c
> > > > > +++ b/drivers/video/backlight/lp855x_bl.c
> > > > > @@ -73,6 +73,7 @@ struct lp855x {
> > > > >            struct device *dev;
> > > > >            struct lp855x_platform_data *pdata;
> > > > >            struct pwm_device *pwm;
> > > > > +       struct regulator *supply;       /* regulator for VDD input */
> > > > >     };
> > > > >
> > > > >     static int lp855x_write_byte(struct lp855x *lp, u8 reg, u8 data)
> > > > > @@ -384,13 +385,6 @@ static int lp855x_parse_dt(struct lp855x *lp)
> > > > >                    pdata->rom_data = &rom[0];
> > > > >            }
> > > > >
> > > > > -       pdata->supply = devm_regulator_get(dev, "power");
> > > > > -       if (IS_ERR(pdata->supply)) {
> > > > > -               if (PTR_ERR(pdata->supply) == -EPROBE_DEFER)
> > > > > -                       return -EPROBE_DEFER;
> > > > > -               pdata->supply = NULL;
> > > > > -       }
> > > > > -
> > > > >            lp->pdata = pdata;
> > > > >
> > > > >            return 0;
> > > > > @@ -431,8 +425,12 @@ static int lp855x_probe(struct i2c_client *cl, const
> > > > > struct i2c_device_id *id)
> > > > >            else
> > > > >                    lp->mode = REGISTER_BASED;
> > > > >
> > > > > -       if (lp->pdata->supply) {
> > > > > -               ret = regulator_enable(lp->pdata->supply);
> > > > > +       lp->supply = devm_regulator_get(lp->dev, "power");
> > > > > +       if (IS_ERR(lp->supply))
> > > > > +               lp->supply = NULL;
> > > >
> > > >
> > > >
> > > > Hi Milo,
> > > > You removed the probe deferral handling on the regulator and broke
> > > > probe deferral in cases where the regulator isn't ready.
> > >
> > >
> > > This power supply is optional. Even if lp855x can not get regulator driver,
> > > it should work. (And I saw same comment in the DT. The 'power-supply'
> > > property is optional). So -EPORBE_DEFER is not necessary in _probe().
> >
> > I respectfully disagree. devm_regulator_get can return EPROBE_DEFER if
> > the regulator is valid (and specified in the dt), but not ready to be
> > used yet. In this case, your patch will assume it doesn't exist and
> > will never use it. This Is Bad.
>
> So do you think this power supply should be mandatory in this driver?

The devm_regulator_get_optinonal() seems the right API for this case.
Let me take a look at and get back to you.

Best regards,
Milo
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