linux-kernel - Re: [Gta04-owner] [PATCH 3/4] usb: phy: twl4030: add support for reading restore on ID pin.

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Message-ID: <20150322170555.5f97f2c2@notabene.brown>
Date:	Sun, 22 Mar 2015 17:05:55 +1100
From:	NeilBrown <neilb@...e.de>
To:	"Dr. H. Nikolaus Schaller" <hns@...delico.com>
Cc:	List for communicating with real GTA04 owners 
	<gta04-owner@...delico.com>, Pavel Machek <pavel@....cz>,
	Tony Lindgren <tony@...mide.com>,
	lkml <linux-kernel@...r.kernel.org>, Felipe Balbi <balbi@...com>,
	Kishon Vijay Abraham I <kishon@...com>,
	Linux OMAP Mailing List <linux-omap@...r.kernel.org>
Subject: Re: [Gta04-owner] [PATCH 3/4] usb: phy: twl4030: add support for
 reading restore on ID pin.

On Wed, 4 Mar 2015 07:54:41 +0100 "Dr. H. Nikolaus Schaller"
<hns@...delico.com> wrote:

> 
> Am 04.03.2015 um 07:35 schrieb NeilBrown <neilb@...e.de>:
> 
> > 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“,
> 
> The international standard for kilo = 1000 is a lower case k.
> While it is (non-standard) to use K for 1024:
> 
> http://en.wikipedia.org/wiki/Kilobyte
> 
> So I would keep the string constants lower case to avoid this potential confusion.

Yes, I got that backwards, didn't I.

I think I'll leave it as lower-case.
I won't include the word "ohm" - it is very uncommon to have units explicit
in sysfs attribute values.

Thanks,
NeilBrown

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