linux-kernel - Re: [PATCH 1/2] regulator: ltc3589: make IRQ optional

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Date:	Fri, 22 Jan 2016 06:41:45 +0100
From:	Lothar Waßmann <LW@...O-electronics.de>
To:	Mark Brown <broonie@...nel.org>
Cc:	Benoît Cousson <bcousson@...libre.com>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	Kumar Gala <galak@...eaurora.org>,
	Liam Girdwood <lgirdwood@...il.com>,
	Mark Rutland <mark.rutland@....com>,
	Pawel Moll <pawel.moll@....com>,
	Rob Herring <robh+dt@...nel.org>,
	Russell King <linux@....linux.org.uk>,
	Tony Lindgren <tony@...mide.com>, devicetree@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	linux-omap@...r.kernel.org
Subject: Re: [PATCH 1/2] regulator: ltc3589: make IRQ optional

Hi,

> On Thu, Jan 21, 2016 at 12:33:11PM +0100, Lothar Waßmann wrote:
> > > On Thu, Jan 21, 2016 at 11:26:11AM +0100, Lothar Waßmann wrote:
> > > > > On Thu, Jan 21, 2016 at 08:05:24AM +0100, Lothar Waßmann wrote:
> > > > > > > On Wed, Jan 20, 2016 at 01:29:51PM +0100, Lothar Waßmann wrote:
> 
> > > > > > > > This pin is used as IRQ pin for the LTC3589 PMIC on the Ka-Ro
> > > > > > > > electronics TX48 module. Make the IRQ optional in the driver and use a
> > > > > > > > polling routine instead if no IRQ is specified in DT.
> > > > > > > > Otherwise the driver will continuously generate interrupts and make
> > > > > > > > the system unusable.
> 
> > It won't. That's the whole purpose of this patch.
> > I'm afraid, I don't quite understand what you want to say...
> 
> Your commit message (quoted above) claims that without this patch if no
> interrupt is supplied then the unsupplied interrupt will somehow be left
> screaming and make the system unusable.  This doesn't make sense, if
> there is no interrupt there is nothing to scream.
> 
"Otherwise" meant the case where the IRQ is specified in DT as is
currently required to get the driver loaded at all.

> > Without this patch there will be a constantly active interrupt, which
> > will stall the system because the nNMI interrupt (on the EXTINTn pin) is
> > level triggered.
> > Since the polarity of the interrupt input is fixed, there is no way to
> > use it in our HW.
> 
> So, contrary to what you've been saying, the interrupt is actually
> connected (and worse, connected to a NMI) but apparently not described
> in DT.  Why is it sensible to make the driver poll (which will affect
> all systems using this device, even those that don't care) and not just
> describe the interrupt in DT so it can be handled promptly in the normal
> fashion?  Presumably this will run into serious problems if the
> interrupt actually fires at runtime since the NMI will scream, it's not
> clear to me how the poll will manage to run successfully in that case.
> 
Currently the driver won't even load without an IRQ specified in DT.
My patch makes it possible to use the driver without requiring an IRQ!


Lothar Waßmann