linux-kernel - Re: [PATCH 1/2] dt-bindings: mmc: mmc-pwrseq-simple: add support for reset control

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Message-ID: <fbdf9165-39b6-4d8f-97ee-a6694d02719d@leica-geosystems.com>
Date: Tue, 8 Oct 2024 07:15:25 +0000
From: POPESCU Catalin <catalin.popescu@...ca-geosystems.com>
To: Rob Herring <robh@...nel.org>
CC: "ulf.hansson@...aro.org" <ulf.hansson@...aro.org>, "krzk+dt@...nel.org"
	<krzk+dt@...nel.org>, "conor+dt@...nel.org" <conor+dt@...nel.org>,
	"p.zabel@...gutronix.de" <p.zabel@...gutronix.de>,
	"linux-mmc@...r.kernel.org" <linux-mmc@...r.kernel.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"m.felsch@...gutronix.de" <m.felsch@...gutronix.de>,
	GEO-CHHER-bsp-development <bsp-development.geo@...ca-geosystems.com>
Subject: Re: [PATCH 1/2] dt-bindings: mmc: mmc-pwrseq-simple: add support for
 reset control

On 07/10/2024 17:59, Rob Herring wrote:
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> On Mon, Oct 07, 2024 at 03:32:42PM +0000, POPESCU Catalin wrote:
>> On 05/10/2024 20:26, Rob Herring wrote:
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>>> On Fri, Oct 04, 2024 at 02:07:39PM +0200, Catalin Popescu wrote:
>>>> Add compatible value "mmc-pwrseq-simple-reset" to support reset control
>>>> instead of gpios. Reset controls being refcounted, they allow to use
>>>> shared resets or gpios across drivers. Support of reset control is
>>>> limited to one single reset control.
>>> Can't you do this without a binding change? Just use reset controls when
>>> there is only 1 GPIO.
>> That's a good question. The idea was to keep in place the gpio support
>> w/o impacting any platform using pwrseq-simple.
> Why would it matter? If not shared, then the behavior should be the
> same. If shared, we want to maintain the broken behavior?
Indeed, you're right. I will provide a new patchset w/o the binding 
change and using reset control for 1 gpio use-case.
>> Also, later on when support for a list of reset gpios will be added to
>> the reset framework, this would not work anymore...
> Why not?
>
> How an OS handles reset-gpios is up to the OS. It can evolve. The
> binding can't evolve because it is an ABI.
>
> Also, a list is kind of broken to begin with for a "generic" binding.
> What's the order the lines should be asserted/deasserted? What about
> timing requirements? You don't know because every device is different.
> This binding would not be accepted now, so extending it is questionable.
>
> Rob