linux-kernel - Re: [RFC patch 2/3] genirq: Add buslock support for irq chips on slow busses

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [day] [month] [year] [list]

Date:	Sat, 15 Aug 2009 16:29:25 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Thomas Gleixner <tglx@...utronix.de>
Cc:	Mark Brown <broonie@...nsource.wolfsonmicro.com>,
	Pavel Machek <pavel@....cz>,
	LKML <linux-kernel@...r.kernel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Dmitry Torokhov <dmitry.torokhov@...il.com>,
	Trilok Soni <soni.trilok@...il.com>,
	Brian Swetland <swetland@...gle.com>,
	Joonyoung Shim <jy0922.shim@...sung.com>,
	m.szyprowski@...sung.com, t.fujak@...sung.com,
	kyungmin.park@...sung.com, David Brownell <david-b@...bell.net>,
	Daniel Ribeiro <drwyrm@...il.com>, arve@...roid.com,
	Barry Song <21cnbao@...il.com>
Subject: Re: [RFC patch 2/3] genirq: Add buslock support for irq chips on
	slow busses


* Thomas Gleixner <tglx@...utronix.de> wrote:

> On Sat, 15 Aug 2009, Ingo Molnar wrote:
> > * Mark Brown <broonie@...nsource.wolfsonmicro.com> wrote:
> > 
> > > On Fri, Aug 14, 2009 at 12:20:49PM +0200, Thomas Gleixner wrote:
> > > > On Fri, 14 Aug 2009, Pavel Machek wrote:
> > > 
> > > > > AFAICT this means that driver would need to know what kind of IRQ it
> > > > > is hooked to, right? That will lead to some ugly code in drivers that
> > > > > can handle both normal and slowbus irqs, right?
> > > 
> > > > Are there such drivers in reality ?
> > > 
> > > Yes.  The GPIO based stuff is the prime example but there's other 
> > > examples - one is the WM831x touchscreen (no driver in mainline 
> > > yet) which can use interrupts via the main interrupt controller on 
> > > the CPU but also has the option of bringing the interrupt signals 
> > > out to dedicated pins on the chip for direct connection to the CPU 
> > > precisely to avoid the overheads of these slow interrupt 
> > > controllers.
> > 
> > This would call for Thomas's first version of the patch, that is 
> > transparent to drivers - the IRQ subsystem will know how to lock 
> > access to the line.
> > 
> > How about implementing that first patch in a cleaner way - can we 
> > somehow express the slow-bus property purely via the irqchip? Or is 
> > that too lowlevel?
> 
> The problem here is that the management functions serialize via 
> irqdesc->lock and call the chip level function with the lock held 
> (preemption and interrupts disabled). So we can not access the 
> slow bus chips from these low level functions.
> 
> If the low level functions just store the information and schedule 
> it for bus access then there is no serialization anymore. Lets 
> look at disable_irq():
> 
> 	spin_lock_irqsave(&desc->lock);
> 	....
> 	desc->chip->mask();
> 		schedule bus access;
> 	...
> 	spin_lock_irqsave(&desc->lock);
> 
> So now we return, but the mask has not reached the chip.
> 
> The idea of bus_lock/bus_sync_unlock() was to provide well defined
> synchronization points for the chip level implementation to do the bus
> update and have this serialized against other management functions.
> 
> 	desc->chip->bus_lock();
> 		Take the chip->bus mutex
> 
> 	spin_lock_irqsave(&desc->lock);
> 	....
> 	desc->chip->mask();
> 		store mask information
> 	...
> 	spin_lock_irqsave(&desc->lock);
> 
> 	desc->chip->bus_sync_unlock();
> 		Update the mask via the slow bus
> 		Release chip->bus mutex
> 
> That way we have made sure that the change to the chip actually 
> hits the hardware before we allow further management operations 
> and it simplifies the code for the chip implementation as the bus 
> access can be done in the context of the caller w/o the need of an 
> extra thread/workqueue ...

Given the alternatives i'd prefer this one now ...

	Ingo
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/