From: Olliver Schinagl <oliver@schinagl.nl>
To: Rob Herring <robh@kernel.org>
Cc: Pawel Moll <pawel.moll@arm.com>,
Mark Rutland <mark.rutland@arm.com>,
Ian Campbell <ijc+devicetree@hellion.org.uk>,
Kumar Gala <galak@codeaurora.org>,
Richard Purdie <rpurdie@rpsys.net>,
Jacek Anaszewski <j.anaszewski@samsung.com>,
"devicetree@vger.kernel.org" <devicetree@vger.kernel.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
Linux LED Subsystem <linux-leds@vger.kernel.org>
Subject: Re: [PATCH 5/6] leds: pca963x: Inform the output that it is inverted
Date: Fri, 22 Apr 2016 17:44:09 +0200 [thread overview]
Message-ID: <D4B039B1-9910-455B-BE8F-50DD9AA7C4EA@schinagl.nl> (raw)
In-Reply-To: <CAL_JsqJdvfrAy+1pYVYOp+tGhjOO3WkQo24+hfxV0_Ncpj6dSg@mail.gmail.com>
On April 22, 2016 3:09:35 PM CEST, Rob Herring <robh@kernel.org> wrote:
>On Fri, Apr 22, 2016 at 7:38 AM, Olliver Schinagl <oliver@schinagl.nl>
>wrote:
>> Hey Rob,
>>
>> On 21-04-16 17:07, Rob Herring wrote:
>>>
>>> On Tue, Apr 19, 2016 at 09:40:49AM +0200, Olliver Schinagl wrote:
>>>>
>>>> When leds are connected in a totem-pole configuration, they can be
>>>> connected either in a active-high, or active-low manor. The driver
>>>> currently always assumes active-high. This patch adds the
>>>> 'nxp,inverted-out' boolean property to tell the driver that the
>leds
>>>> are driven active-low, or rather, that the behavior is inverted to
>what
>>>> is normally expected.
>>>
>>> How do I know what is normally expected?
>>
>> fair point, and in fact, you don't. The text is bad here.
>
>The problem is not so much the text here, but the property is also
>meaningless without some explanation.
>
Well the datasheet states only that it will invert the output. So would it make sense to just state the same here?
>>>
>>>
>>>> Signed-off-by: Olliver Schinagl <oliver@schinagl.nl>
>>>> ---
>>>> Documentation/devicetree/bindings/leds/pca963x.txt | 1 +
>>>> drivers/leds/leds-pca963x.c | 20
>>>> +++++++++++++-------
>>>> include/linux/platform_data/leds-pca963x.h | 1 +
>>>> 3 files changed, 15 insertions(+), 7 deletions(-)
>>>>
>>>> diff --git a/Documentation/devicetree/bindings/leds/pca963x.txt
>>>> b/Documentation/devicetree/bindings/leds/pca963x.txt
>>>> index dafbe99..7b23725 100644
>>>> --- a/Documentation/devicetree/bindings/leds/pca963x.txt
>>>> +++ b/Documentation/devicetree/bindings/leds/pca963x.txt
>>>> @@ -6,6 +6,7 @@ Required properties:
>>>> Optional properties:
>>>> - nxp,totem-pole : use totem pole (push-pull) instead of
>open-drain
>>>> (pca9632 defaults
>>>> to open-drain, newer chips to totem pole)
>>>> + nxp,inverted-out: the connected leds are active-low, default to
>>>> active-high
>>>
>>> Just state what mode you want: nxp,active-low
>>
>> But that's not what happens, which is why my text is bad :) It
>depends on
>> how the board is wired and if it is push-pull or open-drain. Though
>this
>> goes beyond my electronics knowledge. So I'll reduce the text to say
>exactly
>> what we mean, inverted output (or not).
>>
>> Unless you can explain that it would be unrelated and it is actually
>> active-high/low. I'll be more than happy to oblige.
>
>I'm not familiar with this chip, but googling for "active low LED
>circuit" can give you lots of examples. To put it simply, you are
>defining whether the control/switch is on the cathode or anode side of
>the LED. Open-drain vs. push-pull is also related to how the circuit
>is done, but is probably an independent property. I'd think the only
>reason you would use open-drain here is if you wanted to control the
>LED from 2 different signals. Whether you wanted the controls to
>function as OR or AND logic to turn on would determine what the active
>state needs to be.
I was thinking that the output behaves differently depending whether it is configured as push-pull or open-drain.
So to summarize, does the output always go into active-low mode, or does it depend on other parameters as well?
Olliver
>
>Rob
--
Sent from my Android device with K-9 Mail. Please excuse my brevity.
next prev parent reply other threads:[~2016-04-22 15:44 UTC|newest]
Thread overview: 27+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-04-19 7:40 [PATCHv1 0/6] leds: pca9653x: support inverted outputs and cleanups Olliver Schinagl
2016-04-19 7:40 ` [PATCH 1/6] leds: pca963x: Alphabetize headers Olliver Schinagl
2016-04-19 7:40 ` [PATCH 2/6] leds: pca963x: Lock i2c r/w access Olliver Schinagl
2016-04-19 7:40 ` [PATCH 3/6] leds: pca963x: Add defines and remove some magic values Olliver Schinagl
2016-04-19 8:16 ` kbuild test robot
2016-04-19 7:40 ` [PATCH 4/6] leds: pca963x: Reduce " Olliver Schinagl
2016-04-19 7:40 ` [PATCH 5/6] leds: pca963x: Inform the output that it is inverted Olliver Schinagl
2016-04-21 15:07 ` Rob Herring
2016-04-22 12:38 ` Olliver Schinagl
2016-04-22 13:09 ` Rob Herring
2016-04-22 15:44 ` Olliver Schinagl [this message]
2016-04-19 7:40 ` [PATCH 6/6] leds: pca963x: Remove whitespace and checkpatch problems Olliver Schinagl
2016-04-19 9:23 ` [PATCHv1 0/6] leds: pca9653x: support inverted outputs and cleanups Jacek Anaszewski
2016-04-19 9:39 ` Olliver Schinagl
2016-04-19 11:18 ` Ricardo Ribalda Delgado
2016-04-19 13:27 ` Olliver Schinagl
2016-04-19 13:42 ` Ricardo Ribalda Delgado
2016-04-20 7:21 ` Olliver Schinagl
2016-04-20 8:01 ` Ricardo Ribalda Delgado
2016-04-20 8:51 ` Olliver Schinagl
2016-04-20 8:56 ` Ricardo Ribalda Delgado
2016-04-20 9:06 ` Olliver Schinagl
2016-04-20 9:17 ` Ricardo Ribalda Delgado
2016-04-20 10:12 ` Olliver Schinagl
2016-04-22 7:21 ` Olliver Schinagl
2016-05-12 9:04 ` Olliver Schinagl
2016-05-12 9:07 ` Olliver Schinagl
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