linux-kernel - Re: [RFC PATCH v3] reset: Add a defer reset object to send board specific reset

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Date:	Thu, 14 Aug 2014 12:47:38 +0200
From:	Maxime Ripard <maxime.ripard@...e-electrons.com>
To:	Philipp Zabel <p.zabel@...gutronix.de>
Cc:	Linus Walleij <linus.walleij@...aro.org>,
	Houcheng Lin <houcheng@...il.com>,
	Alexandre Courbot <gnurou@...il.com>,
	Grant Likely <grant.likely@...aro.org>,
	Rob Herring <robh+dt@...nel.org>,
	Dmitry Eremin-Solenikov <dbaryshkov@...il.com>,
	David Woodhouse <dwmw2@...radead.org>,
	Stephen Gallimore <stephen.gallimore@...com>,
	Srinivas KANDAGATLA <srinivas.kandagatla@...com>,
	Ulf Hansson <ulf.hansson@...aro.org>, sre@...nel.org,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	"linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
	Vikas Sajjan <vikas.sajjan@...sung.com>,
	linux-samsung-soc <linux-samsung-soc@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [RFC PATCH v3] reset: Add a defer reset object to send board
 specific reset

On Thu, Aug 14, 2014 at 11:36:38AM +0200, Philipp Zabel wrote:
> Hi Maxime,
> 
> Am Montag, den 11.08.2014, 19:33 +0200 schrieb Maxime Ripard:
> > > Mostly because Maxime and I seem to have a completely different opinion
> > > and nobody else argued one way or the other.
> > 
> > Yep, mostly because I don't see how a generic approach can work.
> > 
> > The existing reset-gpios property only provide the gpio to use, but
> > some informations are encoded in the driver, such as the reset
> > duration, or a reset sequence if any.
> 
> The driver should provide the duration.

How? This used to be in the code, and reset_control_reset doesn't take
such argument.

> I'd really like to see an example where sequencing is necessary.

Well, if you have several reset lines, the sequencing between each
might be important.

> I agree that as soon as things get significantly more complicated than
> pulsing a single GPIO, the reset-gpios binding is too limited.

While the generic reset bindings are perfect for that.

> Still, I'm not happy to mandate a separate gpio reset device for each
> reset line if most devices are simple enough for it to work without.

Well, it's pretty much already the case for other subsystems, such as
regulator.

I guess we can treat this as a legacy option, but allow the reset-gpio
code to be a full driver of its own, if we need more advanced use
cases?

> What about using reset-gpios for the majority of simple cases and have a
> separate gpio-reset-sequencer driver when multiple GPIO resets have to
> be timed?

I don't know. I feel like it should be in the driver itself, rather
than in a generic layer.

Maxime

-- 
Maxime Ripard, Free Electrons
Embedded Linux, Kernel and Android engineering
http://free-electrons.com

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