Date:   Wed, 31 Jan 2018 11:24:34 +0200
From:   Peter Ujfalusi <peter.ujfalusi@...com>
To:     Ladislav Michl <ladis@...ux-mips.org>, Pavel Machek <pavel@....cz>
CC:     <mark.rutland@....com>, <alsa-devel@...a-project.org>,
        <lgirdwood@...il.com>, <tony@...mide.com>, <abcloriens@...il.com>,
        <tiwai@...e.com>, <martijn@...xit.nl>,
        Filip Matijević <filip.matijevic.pz@...il.com>,
        <patrikbachan@...il.com>, <ivo.g.dimitrov.75@...il.com>,
        <khilman@...nel.org>, <linux-omap@...r.kernel.org>,
        <serge@...lyn.com>, <devicetree@...r.kernel.org>,
        <pali.rohar@...il.com>, <robh+dt@...nel.org>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        <aaro.koskinen@....fi>, <linux-kernel@...r.kernel.org>,
        <broonie@...nel.org>, <clayton@...ftyguy.net>,
        <sakari.ailus@...ux.intel.com>, <sre@...nel.org>,
        <bhumirks@...il.com>
Subject: Re: [alsa-devel] [PATCH] sound/tlv320dac33: Add device tree support

On 2018-01-30 13:38, Ladislav Michl wrote:
> On Tue, Jan 30, 2018 at 11:35:38AM +0100, Pavel Machek wrote:
>> On Tue 2018-01-30 11:10:46, Ladislav Michl wrote:
>>> On Tue, Jan 30, 2018 at 11:00:23AM +0100, Pavel Machek wrote:
>>>> On Tue 2018-01-30 10:38:38, Ladislav Michl wrote:
>>>>> On Tue, Jan 30, 2018 at 10:11:02AM +0100, Filip Matijević wrote:
>>>>>> Hi,
>>>>>>
>>>>
>>>>>>> Well, notice I'm converting existing driver to device tree. And that
>>>>>>> one already has GPIO dependency. It is possible that more work needs
>>>>>>> to be done there, but that should not be a reason to delay this. Feel
>>>>>>> free to help.
>>>>>
>>>>> Adding DT properties that need to be maintained for compatibility reasons
>>>>> is a bad idea and very good reason to delay merging unfinished stuff.
>>>>> And meanwhile it turned out it is not power-gpio :)
>>>>
>>>> I believe reset-gpios and power-gpios are commonly used like
>>>> this... and that's what the old code does.
>>>
>>> Why do you care about old code when introducing new DT property?
>>> Either it is reset, then lets call it reset-gpios or it is power supply
>>> and then voltage regulator should be used (VAUX4.OUT is such a regulator
>>> although it is unclear to me how it is controlled (*)).
>>
>> power gpio = !reset gpio. Difference is only in polarity.
> 
> Quick grep:
> Documentation/devicetree/bindings/net/smsc-lan91c111.txt
> - power-gpios: GPIO to control the PWRDWN pin
> - reset-gpios: GPIO to control the RESET pin
> Documentation/devicetree/bindings/net/wireless/ti,wl1251.txt
> - ti,power-gpio :     GPIO connected to chip's PMEN pin
> Documentation/devicetree/bindings/input/touchscreen/silead_gsl1680.txt
> - power-gpios             : Specification for the pin connected to the gsl1680's
>                             shutdown input. This needs to be driven high to take the
>                             gsl1680 out of its low power state
> Documentation/devicetree/bindings/input/touchscreen/ektf2127.txt
> - power-gpios             : GPIO specification for the pin connected to the
>                             ektf2127's wake input. This needs to be driven high
>                             to take ektf2127 out of it's low power state
> 
> As you can see others are using it to drive pins different from nRESET. As
> stated in datasheet:
> "The TLV320DAC32 requires a hardware reset after power-up for proper operation.
> After all power supplies are at their specified values, the nRESET pin must be
> driven low for at least 10ns. If this reset sequence is not performed, the DAC32
> may not respond properly to register reads/writes". That does not sound like
> anything to do with power.
> 
> (It seems the only difference between TLV320DAC33 and TLV320DAC32 is uses a ball
> grid array package vs QFN32)

Note that tlv320dac32 != tlv320dac33, they are not even register
compatible devices... dac33 was created _for_ Nokia back in the days and
as far as I know there is no publicly available documentation for dac33.

And yes, my pick to use power_gpio in the code was wrong, it should have
been named as reset_gpio.

> 
>>>> You are not helping.
>>>
>>> The only way I can help here is to resend your patch with "reset-gpios"
>>> used, which I'm pretty sure you can handle yourself.
>>
>> Well, you can do that, and then you can argue with the next person who
>> feels one of the properties has to get his preferred color. Hard part
>> is not changing code :-(.
> 
> Indeed, hard part is not to break DT compatibility later. Consider someone
> will have to add regulator support later, which you omitted to do - having
> both power supply and power gpio is a bit confusing, don't you think?
> 
> Anyway, time to stop arguing, feel free to do what you think is right, I do
> not have anything important to add :)
> 
> 	ladis
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> 

- Péter

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