linux-kernel - Re: [RFC PATCH 1/4] dt-binding: i2c: add generic properties for GPIO bus recovery

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Message-ID: <b3a04528-0053-16bf-f092-147685298ced@microchip.com>
Date:   Mon, 27 Jul 2020 10:44:57 +0000
From:   <Codrin.Ciubotariu@...rochip.com>
To:     <linux@...linux.org.uk>, <wsa@...nel.org>
CC:     <linux-i2c@...r.kernel.org>, <devicetree@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>,
        <linux-arm-kernel@...ts.infradead.org>, <robh+dt@...nel.org>,
        <Ludovic.Desroches@...rochip.com>, <Nicolas.Ferre@...rochip.com>,
        <alexandre.belloni@...tlin.com>, <kamel.bouhara@...tlin.com>
Subject: Re: [RFC PATCH 1/4] dt-binding: i2c: add generic properties for GPIO
 bus recovery

On 24.07.2020 23:52, Russell King - ARM Linux admin wrote:
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> 
> On Fri, Jul 24, 2020 at 09:39:13PM +0200, Wolfram Sang wrote:
>> On Sun, Jul 05, 2020 at 11:19:18PM +0200, Wolfram Sang wrote:
>>>
>>>> +- pinctrl
>>>> + add extra pinctrl to configure SCL/SDA pins to GPIO function for bus
>>>> + recovery, call it "gpio" or "recovery" state
>>>
>>> I think we should stick with "gpio" only. That is what at91 and imx have
>>> in their bindings. pxa uses "recovery" as a pinctrl state name but I
>>> can't find any further use or documentation of that. PXA is not fully
>>> converted to the best of my knowledge, so maybe it is no problem for PXA
>>> to switch to "gpio", too? We should ask Russell King (cced).
> 
> Fully converted to what?  The generic handling where the i2c core layer
> handles everything to do with recovery, including the switch between
> modes?
> 
> i2c-pxa _intentionally_ carefully handles the switch between i2c mode and
> GPIO mode, and I don't see a generic driver doing that to avoid causing
> any additional glitches on the bus.  Given the use case that this recovery
> is targetted at, avoiding glitches is very important to keep.

Why is it not possbile to handle glitches in a generic way? I guess it 
depends on the pinctl, but we could treat a worst-case scenario to 
assure the switch between states is done properly.

> 
>>> Russell, do you object naming the pinctrl state for bus recovery in
>>> the pxa i2c driver from "recovery" to "gpio"?
>>
>> No response, so far. I suggest now to support the "recovery" naming but
>> mark it as deprecated. Opinions?
> 
> I don't have a preference on the exact naming.
> 
> --
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