From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from gate.crashing.org (gate.crashing.org [63.228.1.57]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (Client did not present a certificate) by ozlabs.org (Postfix) with ESMTP id 8DADBDDE9A for ; Sat, 20 Oct 2007 14:09:19 +1000 (EST) Subject: Re: [PATCH] synchronize_irq needs a barrier From: Benjamin Herrenschmidt To: Linus Torvalds In-Reply-To: <1192853044.17235.32.camel@pasglop> References: <1192670742.12879.5.camel@pasglop> <200710200402.43106.maximlevitsky@gmail.com> <1192853044.17235.32.camel@pasglop> Content-Type: text/plain Date: Sat, 20 Oct 2007 14:09:10 +1000 Message-Id: <1192853350.17235.37.camel@pasglop> Mime-Version: 1.0 Cc: linuxppc-dev list , akpm , Maxim Levitsky , Linux Kernel list Reply-To: benh@kernel.crashing.org List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , > > - even when you ignore the interrupt (because the driver doesn't care, > > it's suspending), you need to make sure the hardware gets shut up by > > reading (or writing) the proper interrupt status register. > > > > Otherwise, with a level interrupt, the interrupt will continue to be > > held active ("screaming") and the CPU will get interrupted over and > > over again, until the irq subsystem will just turn the irq off > > entirely. > > His suspend routine wrote to the IRQ mask (or equivalent) register in > his code example, thus the HW should shut up eventually, thus that isn't > strictly necessary, the IRQ in that case is just a "short > interrupt" (noticed by the PIC and delivered but possibly not asserted > anymore at this stage or about to go down). In fact, he -must not- ack it. Because is the HW is really down (in D3), got knows what accessing the ACK register will do. I can give you ideas... from nothing on most x86 desktops to machine checks on most powerpc machines, though I could imagine some cards bad enough to lock your bus up if you try to access a register while they are in D3 (I've seen some of those critters and it seems not all bridges timeout on cards that just keep sending retries). Cheers, Ben.