linux-kernel - Re: [PATCH 8/8] ARM: tegra: HACK: remove set_irq

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Message-ID: <20120301210020.GC19274@n2100.arm.linux.org.uk>
Date:	Thu, 1 Mar 2012 21:00:20 +0000
From:	Russell King - ARM Linux <linux@....linux.org.uk>
To:	Arnd Bergmann <arnd@...db.de>
Cc:	Stephen Warren <swarren@...dia.com>, Alan Ott <alan@...nal11.us>,
	Colin Cross <ccross@...roid.com>,
	Olof Johansson <olof@...om.net>,
	Grant Likely <grant.likely@...retlab.ca>,
	Linus Walleij <linus.walleij@...ricsson.com>,
	Alan Stern <stern@...land.harvard.edu>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Lucas De Marchi <lucas.demarchi@...fusion.mobi>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-tegra@...r.kernel.org" <linux-tegra@...r.kernel.org>,
	"linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>
Subject: Re: [PATCH 8/8] ARM: tegra: HACK: remove set_irq_flags() from
	driver

On Thu, Mar 01, 2012 at 08:38:27PM +0000, Arnd Bergmann wrote:
> On Thursday 01 March 2012, Stephen Warren wrote:
> > 
> > Alan Ott wrote at Thursday, March 01, 2012 12:27 PM:
> > > From: Arnd Bergmann <arnd@...db.de>
> > > 
> > > The driver should not call set_irq_flags itself, and
> > 
> > Probably true in this case.
> > 
> > > cannot do this from a loadable module.
> > 
> > I hope that's not true; grep'ing the entire of drivers/ shows a bunch
> > of drivers calling this function, and many look like they'd be reasonable
> > as module.
> 
> The drivers that I can see using it are for the most part implementing
> irq controllers by themselves, which is different from merely using an
> interrupt.
> 
> There are three exceptions today:
> 
> arnd@...ppe2:~/linux-arm$ git grep -l set_irq_flags  drivers/ | xargs grep -L irq_chip
> drivers/tty/serial/serial_ks8695.c

Setting NOAUTOEN should be done elsewhere (in platform code.)  Better
still, fixing genirq to allow request_irq() to permit the interrupt
to be requested *without enabling it* would be a step forwards.  I
thought my original ARM IRQ code did that.

> drivers/tty/serial/sirfsoc_uart.c

Same issue, so same comments.

> drivers/usb/host/ehci-tegra.c

This one should not be there.  Having drivers mark IRQs as being
requestable when the whole point of the flag is to stop request_irq()
being used on non-initialized interrupts is just plain stupid.

> > From what little I understand of this, any irq_chip is going to call
> > that function after setting up any child/cascaded IRQs, and I assume
> > that irq_chips can be in modules.
> 
> But the function is not exported. I guess if we want to allow
> irq_chips in loadable modules, we could export it, but I don't see
> how it could ever have worked so far.

genirq does not permit flow handlers in modules - I suspect that's
because it's pretty hard to remove them safely from the system without
a lot of effort.  Certainly, a whole bunch of genirq functions which
are required to implement external flow handlers etc aren't exported.
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