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

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Message-ID: <20241021065258.w56zhl7y3loanjwi@pengutronix.de>
Date: Mon, 21 Oct 2024 08:52:58 +0200
From: Marco Felsch <m.felsch@...gutronix.de>
To: Rob Herring <robh@...nel.org>
Cc: POPESCU Catalin <catalin.popescu@...ca-geosystems.com>,
	"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>,
	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 24-10-07, Rob Herring wrote:
> On Mon, Oct 07, 2024 at 03:32:42PM +0000, POPESCU Catalin wrote:
> > On 05/10/2024 20:26, Rob Herring wrote:
> > > [Some people who received this message don't often get email from robh@...nel.org. Learn why this is important at https://aka.ms/LearnAboutSenderIdentification ]
> > >
> > > This email is not from Hexagon’s Office 365 instance. Please be careful while clicking links, opening attachments, or replying to this email.
> > >
> > >
> > > 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?

My two cents on this. This will break systems which haven't the
RESET_GPIO driver enabled yet. Therefore we may get regressions mails.
I'm fine with it if that is okay.

Regards,
  Marco

> > 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
>