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

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Date:	Thu, 1 Mar 2012 20:38:27 +0000
From:	Arnd Bergmann <arnd@...db.de>
To:	Stephen Warren <swarren@...dia.com>
Cc:	Alan Ott <alan@...nal11.us>, Russell King <linux@....linux.org.uk>,
	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 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
drivers/tty/serial/sirfsoc_uart.c
drivers/usb/host/ehci-tegra.c

> 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.
 
> > Remove the call for now, which might break the driver
> > but at least lets the kernel link again.
> 
> The driver appears to work fine with this removed. At least, on Tegra20
> Harmony, I was able to modprobe ehci-hcd and then use the USB Ethernet
> controller for DHCP and SSH.

Ok, maybe it was the right fix after all then and it just needs a proper
change description ;-)

	Arnd
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