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: <BF76BA84-5DD6-499D-8A00-E787C843BF7F@goldelico.com>
Date:	Wed, 4 Mar 2015 07:54:41 +0100
From:	"Dr. H. Nikolaus Schaller" <hns@...delico.com>
To:	List for communicating with real GTA04 owners 
	<gta04-owner@...delico.com>, NeilBrown <neilb@...e.de>
Cc:	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.

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.

> 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
> _______________________________________________
> Gta04-owner mailing list
> Gta04-owner@...delico.com
> http://lists.goldelico.com/mailman/listinfo.cgi/gta04-owner

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