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

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Date:	Sat, 11 Jul 2015 05:52:22 +0900
From:	"Kim, Milo" <milo.kim@...com>
To:	Sean Paul <seanpaul@...omium.org>
CC:	Jingoo Han <jingoohan1@...il.com>,
	Lee Jones <lee.jones@...aro.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] backlight: lp855x: use private data for regulator
 control

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@...com> 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@...com> 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@...omium.org>
>>>> Cc: Jingoo Han <jingoohan1@...il.com>
>>>> Cc: Lee Jones <lee.jones@...aro.org>
>>>> Cc: linux-kernel@...r.kernel.org
>>>> Signed-off-by: Milo Kim <milo.kim@...com>
>>>> ---
>>>>    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?

Best regards,
Milo
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