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

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Message-ID: <20241007155939.GA849826-robh@kernel.org>
Date: Mon, 7 Oct 2024 10:59:39 -0500
From: Rob Herring <robh@...nel.org>
To: POPESCU Catalin <catalin.popescu@...ca-geosystems.com>
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 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?

> 
> 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