linux-kernel - Re: [PATCH v2 0/6] ARM: STi reset controller support

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Date:	Mon, 24 Feb 2014 16:16:22 +0100
From:	Philipp Zabel <p.zabel@...gutronix.de>
To:	srinivas kandagatla <srinivas.kandagatla@...com>
Cc:	Maxime Coquelin <maxime.coquelin@...com>,
	Mark Rutland <mark.rutland@....com>,
	devicetree@...r.kernel.org, Russell King <linux@....linux.org.uk>,
	kernel@...inux.com, Pawel Moll <pawel.moll@....com>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	Olof Johansson <olof@...om.net>, linux-doc@...r.kernel.org,
	linux-kernel@...r.kernel.org, stephen.gallimore@...com,
	Rob Herring <robh+dt@...nel.org>,
	Arnd Bergmann <arnd@...db.de>, Rob Landley <rob@...dley.net>,
	Kumar Gala <galak@...eaurora.org>,
	Grant Likely <grant.likely@...aro.org>,
	linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v2 0/6] ARM: STi reset controller support

Hi Srinivas,

Am Montag, den 24.02.2014, 14:03 +0000 schrieb srinivas kandagatla:
> Thanks Philipp for your comments,
> 
> On 24/02/14 10:33, Philipp Zabel wrote:
> >> > Did Srini's explanations convinced you?
> >> > 
> >> > If so, could you queue the series for v3.15?
> > to be honest, I'm not comfortable with this explanation. If the
> > "powerdown" bits only gate the clocks to those modules, calling it a
> > reset control is clearly the wrong abstraction. If that is the case,
> > couldn't you handle those bits via the clock framework?
> I just had a re-look at the IPs specs for more information on where
> these power-down signals are actually terminating on the IP side.
> 
> For example: ST-Synopsis Ethernet GMAC IP has two pins
> power_down_req[IN] and power_down_ack[OUT]. power_down_req is used by
> the software to either put the IP in powerdown or bring it out of
> powerdown state.

Now I'm a bit confused. There is no mention of GMAC in your patches,
and for ETH[01] they contain only the SOFTRESET bits. I have no issue
with the SOFTRESETs.

> The IP itself drives power_down_ack to indicate when the power down
> request is successfully finished. For power_down/power_up request the IP
> will change the internal state accordingly including powering up/down
> its internal blocks and/or clock gating.
> 
> > If on the other hand these powerdown bits also trigger reset machinery,
> > such that asserting and deasserting that bit will change the module's
> > internal state, I could be convinced to queue them like this.
> This is true with ST IPs, these lines change the state of the IP as
> described above. Reset framework seems to fits in very well with this
> behavior rather than power-domains or clock framework.

If you put the IP in power down when it is idle, and then power it up
again, will the IP registers have kept their previous state?

regards
Philipp

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