linux-kernel - Re: [PATCH v2 2/5] extcon: arizona: Add basic microphone detection DT/ACPI bindings

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Date:	Fri, 19 Jun 2015 11:44:53 +0100
From:	Charles Keepax <ckeepax@...nsource.wolfsonmicro.com>
To:	cw00.choi@...sung.com
Cc:	Lee Jones <lee.jones@...aro.org>,
	"myungjoo.ham@...sung.com" <myungjoo.ham@...sung.com>,
	Samuel Ortiz <sameo@...ux.intel.com>,
	devicetree <devicetree@...r.kernel.org>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	patches@...nsource.wolfsonmicro.com
Subject: Re: [PATCH v2 2/5] extcon: arizona: Add basic microphone detection
	DT/ACPI bindings

On Fri, Jun 19, 2015 at 07:31:49PM +0900, Chanwoo Choi wrote:
> On Fri, Jun 19, 2015 at 6:08 PM, Charles Keepax
> <ckeepax@...nsource.wolfsonmicro.com> wrote:
> > On Fri, Jun 19, 2015 at 05:28:11PM +0900, Chanwoo Choi wrote:
> >> On Fri, Jun 19, 2015 at 5:17 PM, Charles Keepax
> >> <ckeepax@...nsource.wolfsonmicro.com> wrote:
> >> > On Fri, Jun 19, 2015 at 11:25:57AM +0900, Chanwoo Choi wrote:
> >> >> Hi Charles,
> >> >>
> >> >> On Thu, Jun 18, 2015 at 11:43 PM, Charles Keepax
> >> >> <ckeepax@...nsource.wolfsonmicro.com> wrote:
> >> >> > This patch adds bindings for the basic microphone detection platform
> >> >> > data.
> >> >> >
> >> >> > Signed-off-by: Charles Keepax <ckeepax@...nsource.wolfsonmicro.com>
> >> >> > ---
> >> >> > +       dbtime = 0;
> >> >> > +       device_property_read_u32(arizona->dev, "wlf,micd-dbtime", &dbtime);
> >> >> > +       switch (dbtime) {
> >> >> > +       case 2:
> >> >>
> >> >> I'd like you to define the constant variable for specific integer
> >> >> value to improve the readability.
> >> >> e.g.,
> >> >>
> >> >> #define MICD_DBTIME_XXX 2
> >> >> #define MICD_DBTIME_XXX 4
> >> >>
> >> >> > +               pdata->micd_dbtime = 0x10000;
> >> >>
> >> >> Also, you better to define the constant variable for "0x10000" to
> >> >> improbe readability in the include/linux/mfd/arizona.h. If you just
> >> >> use the hex value, the other developer cannot analyze the meaning of
> >> >> "0x10000".
> >> >>
> >> >> > +               break;
> >> >> > +       case 4:
> >> >>
> >> >> ditto.
> >> >>
> >> >
> >> > I am not sure these two really warrant a define the number in DT
> >> > indicates the number of debounces to perform.
> >> >
> >> > #define MICD_DBTIME_TWO 2
> >>
> >> No. I mean that you should define the appropriate name of definition
> >> to indicate the meaning of 2 or 4. Just not 2 -> TWO.
> >>
> >> 2 is 2 second? or 2 is milli-second? or Is there any other meaning?
> >> I can never know the meaning of '2' without any description and any
> >> proper name of definition.
> >
> > It is literally two, two debounces, I really can't see what I
> > could call the define. What do you think to the idea I suggested
> > to rename the variable dbtime -> num_debounces?
> 
> Is it either "debounce time" or "the number of debounce"?
> 
> Also,
> 
> When extcon-arizona driver update the bit for micd_dbtime, use the
> ARIZONA_MICD_DBTIME_MASK (0x0002).
> 
> In following case, 0x10000 is larger than ARIZONA_MICD_DBTIME_MASK(0x0002).
> 
>           case 2:
>                 pdata->micd_dbtime = 0x10000;
> 
> Is it correct?
> 
> I thinkt that "arizona->pdata.micd_dbtime <<
> ARIZONA_MICD_DBTIME_SHIFT" value should be included in the range of
> ARIZONA_MICD_DBTIME_MASK(0x0002).

Basically this boils down to setting a single bit which chooses
between 2 and 4 debounces. The tricky thing is that the default
value for the pdata will be 0, and the value of the bit for 2
debounces will be 0. So inorder to show we have intentionally set
the pdata we set a value that is non-zero but won't get written
into the register. It is a little awkward but I don't want to
change how the pdata works as there are probably systems out of
tree that use it.

Thanks,
Charles
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