linux-kernel - Re: [PATCH 1/2] dt-bindings: i2c-mux-gpio: Add optional DT property

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Date:   Tue, 26 Oct 2021 23:16:11 +0200
From:   Peter Rosin <peda@...ntia.se>
To:     Rob Herring <robh@...nel.org>,
        Horatiu Vultur <horatiu.vultur@...rochip.com>
Cc:     peter.korsgaard@...co.com, lars.povlsen@...rochip.com,
        linux-i2c@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] dt-bindings: i2c-mux-gpio: Add optional DT property



On 2021-10-26 23:02, Peter Rosin wrote:
> 
> 
> On 2021-10-26 22:29, Rob Herring wrote:
>> On Wed, Oct 13, 2021 at 04:10:02PM +0200, Horatiu Vultur wrote:
>>> Add optional property 'select-delay' DT property. In case this is set
>>> then a delay is added when changing mux state. The value is specified in
>>> usec.
>>>
>>> Signed-off-by: Horatiu Vultur <horatiu.vultur@...rochip.com>
>>> ---
>>>  Documentation/devicetree/bindings/i2c/i2c-mux-gpio.txt | 1 +
>>>  1 file changed, 1 insertion(+)
>>>
>>> diff --git a/Documentation/devicetree/bindings/i2c/i2c-mux-gpio.txt b/Documentation/devicetree/bindings/i2c/i2c-mux-gpio.txt
>>> index d4cf10582a26..d0dacbad491a 100644
>>> --- a/Documentation/devicetree/bindings/i2c/i2c-mux-gpio.txt
>>> +++ b/Documentation/devicetree/bindings/i2c/i2c-mux-gpio.txt
>>> @@ -28,6 +28,7 @@ Required properties:
>>>  Optional properties:
>>>  - idle-state: value to set the muxer to when idle. When no value is
>>>    given, it defaults to the last value used.
>>> +- select-delay: GPIO settle delay when changing mux state. In usec.
>>
>> Seems generally useful. Can we add this first to the mux control 
>> binding, then use it here (or better yet, use the mux binding if you 
>> can instead).
> 
> It is actually not very useful here, nor in the mux-control binding. The
> same gpio lines (or mux-control) could be used to control several muxes,
> all with vastly different needs as to how long the settle time needs to
> be. I.e. it is not the gpio lines (or mux-control) that need to settle,
> it is the signal(s) that travel through the controlled mux(es) that need
> to settle.
> 
> In this case, a settle time property was added to the io-channel-mux
> binding, which makes much more sense.
> 
> https://git.kernel.org/pub/scm/linux/kernel/git/gregkh/char-misc.git/commit/Documentation/devicetree/bindings/iio/multiplexer/io-channel-mux.yaml?h=char-misc-next&id=b9221f71c285

Oh crap, sorry. This series went right past me since it somehow didn't get
flagged in my inbox. But Robs answer did, and then I assumed it was a late
answer to this series:

https://lore.kernel.org/lkml/20211004153640.20650-1-vincent.whitchurch@axis.com/

Which it of course isn't. But in my mind it was. Result: my above response
does not make any sense. I'll have to go to bed now, but I promise to write
a proper answer tomorrow.

Cheers,
Peter

> Cheers,
> Peter
> 
>> Also, properties with units need a standard unit suffix.
>>
>>>  
>>>  For each i2c child node, an I2C child bus will be created. They will
>>>  be numbered based on their order in the device tree.
>>> -- 
>>> 2.33.0
>>>
>>>