linux-kernel - Re: [PATCH v5 2/2] i2c: mv64xxx: add an optional bus-reset-gpios property

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Message-ID: <8ffbd670-52c5-4344-9119-d7e55367092b@alliedtelesis.co.nz>
Date:   Sun, 29 Oct 2023 21:02:31 +0000
From:   Chris Packham <Chris.Packham@...iedtelesis.co.nz>
To:     Andi Shyti <andi.shyti@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
CC:     "gregory.clement@...tlin.com" <gregory.clement@...tlin.com>,
        "robh+dt@...nel.org" <robh+dt@...nel.org>,
        "krzysztof.kozlowski+dt@...aro.org" 
        <krzysztof.kozlowski+dt@...aro.org>,
        "conor+dt@...nel.org" <conor+dt@...nel.org>,
        Abel Vesa <abel.vesa@...aro.org>,
        Mark Brown <broonie@...nel.org>,
        "linux-i2c@...r.kernel.org" <linux-i2c@...r.kernel.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v5 2/2] i2c: mv64xxx: add an optional bus-reset-gpios
 property


On 28/10/23 01:55, Andi Shyti wrote:
> Hi Krzysztof,
>
> On Fri, Oct 27, 2023 at 01:37:05PM +0200, Krzysztof Kozlowski wrote:
>> On 27/10/2023 13:27, Krzysztof Kozlowski wrote:
>>> On 27/10/2023 05:31, Chris Packham wrote:
>>>> Some hardware designs have a GPIO used to control the reset of all the
>>>> devices on and I2C bus. It's not possible for every child node to
>>>> declare a reset-gpios property as only the first device probed would be
>>>> able to successfully request it (the others will get -EBUSY). Represent
>> Cc: Mark,
>>
>> Also this part is not true. If the bus is non-discoverable, then it is
>> possible to have reset-gpios in each probed device. You can share GPIOs,
>> so no problem with -EBUSY at all.
>>
>> The problem is doing reset:
>> 1. in proper moment for all devices
>> 2. without affecting other devices when one unbinds/remove()
> yes, I thought that we could get to this point, but I did not
> object the patch as I didn't see an immediate better solution. I
> would still be OK to merge it until we develop something better.
>
> Let me mull this over and will be back to the topic.

If we're happy with plain GPIOs I can move what I've done so far to 
somewhere in the I2C core. I know we've got other hardware designs with 
different controllers that also have muxes connected to a common reset 
GPIO so I would have ended up moving this code to I2C core eventually.

If we're talking a proper reset driver implemented using GPIOs then that 
might be a bit of bigger task.

> Thanks, Krzysztof!
> Andi
>
>> The (2) above is not solveable easy in kernel and we already had nice
>> talks about it just few days ago:
>> 1. Apple case:
>> https://scanmail.trustwave.com/?c=20988&d=1LO75R2nre1LP3TyEWMYg1Is4Mz-YROPQ8JxsJqwkg&u=https%3a%2f%2fsocial%2etreehouse%2esystems%2f%40marcan%2f111268780311634160
>>
>> 2. my WSA884x:
>> https://scanmail.trustwave.com/?c=20988&d=1LO75R2nre1LP3TyEWMYg1Is4Mz-YROPQ8IvtMfhyQ&u=https%3a%2f%2flore%2ekernel%2eorg%2falsa-devel%2f84f9f1c4-0627-4986-8160-b4ab99469b81%40linaro%2eorg%2f
>>
>> Last,
>> I would like to apologize to you Chris. I understand that bringing such
>> feedback at v5 is not that good. I had plenty of time to say something
>> earlier, so this is not really professional from my side. I am sorry,
>> just my brain did not connect all these topics together.
>>
>> I apologize.
>>
>> Best regards,
>> Krzysztof