linux-kernel - Re: [PATCH 3/4] usb: phy: twl4030: add support for reading restore on ID pin.

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Date:	Wed, 4 Mar 2015 17:35:51 +1100
From:	NeilBrown <neilb@...e.de>
To:	Pavel Machek <pavel@....cz>
Cc:	Tony Lindgren <tony@...mide.com>, Felipe Balbi <balbi@...com>,
	Kishon Vijay Abraham I <kishon@...com>,
	linux-omap@...r.kernel.org, lkml <linux-kernel@...r.kernel.org>,
	GTA04 owners <gta04-owner@...delico.com>
Subject: Re: [PATCH 3/4] usb: phy: twl4030: add support for reading restore
 on ID pin.

On Mon, 2 Mar 2015 22:04:31 +0100 Pavel Machek <pavel@....cz> wrote:

> Hi!
> 
> > The twl4030 phy can measure, with low precision, the
> > resistance-to-ground of the ID pin.
> > 
> > Add a function to read the value, and export the result
> > via sysfs.
> > 
> > If the read fails, which it does sometimes, try again in 50msec.
> > 
> > Signed-off-by: NeilBrown <neilb@...e.de>
> > ---
> >  drivers/phy/phy-twl4030-usb.c |   63 +++++++++++++++++++++++++++++++++++++++++
> >  1 file changed, 63 insertions(+)
> > 
> > diff --git a/drivers/phy/phy-twl4030-usb.c b/drivers/phy/phy-twl4030-usb.c
> > index 023fe150c7a1..759950898df9 100644
> > --- a/drivers/phy/phy-twl4030-usb.c
> > +++ b/drivers/phy/phy-twl4030-usb.c
> > @@ -374,6 +374,56 @@ static void twl4030_i2c_access(struct twl4030_usb *twl, int on)
> >  	}
> >  }
> >  
> > +enum twl4030_id_status {
> > +	TWL4030_GROUND,
> > +	TWL4030_102K,
> > +	TWL4030_200K,
> > +	TWL4030_440K,
> > +	TWL4030_FLOATING,
> > +	TWL4030_ID_UNKNOWN,
> > +};
> > +static char *twl4030_id_names[] = {
> > +	"ground",
> > +	"102k",
> > +	"200k",
> > +	"440k",
> 
> New /sys files should be documented somewhere...?

Preferably with the code...

> 
> Does it make sense to change "440k" -> "440KOhm"?

Interesting question.  I prefer to avoid including units in files - bare
numbers is better.  But there is no number to match "floating" unless I spell
it out as "infinity", and wouldn't be helpful.

Certainly "K" would be preferred over "k", and given that I have "ground"
and  "floating", it is more consistent to include the "Ohm"....

These are really names, not measures of resistance.  The data sheet calls
them:
 ID_RES_FLOAT  (or sometimes ID_FLOAT)
 ID_RES_440K
 ID_RES_200K
 ID_RES_102K
 ID_GND        (or sometimes ID_RES_GND)

So using those names is defensible.

I think I'll change them all to upper case, but leave out the "Ohm".
My justification is consistency with the data sheet.




> 
> Plus I guess you need to update Documentation/

I guess I'll need to give in to this eventually :-)

> 
> Acked-by: Pavel Machek <pavel@....cz>
> 

Thanks,
NeilBrown

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