From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from imap.sh.mvista.com (unknown [63.81.120.155]) by ozlabs.org (Postfix) with ESMTP id 555BC67BE8 for ; Mon, 20 Nov 2006 07:38:32 +1100 (EST) Message-ID: <4560C121.30403@ru.mvista.com> Date: Sun, 19 Nov 2006 23:40:01 +0300 From: Sergei Shtylyov MIME-Version: 1.0 To: Benjamin Herrenschmidt Subject: Re: [PATCH] 2.6.18-rt7: PowerPC: fix breakage in threaded fasteoi type IRQ handlers References: <200611192243.34850.sshtylyov@ru.mvista.com> <1163966437.5826.99.camel@localhost.localdomain> <20061119200650.GA22949@elte.hu> <1163967590.5826.104.camel@localhost.localdomain> <4560BDF5.400@ru.mvista.com> <1163968376.5826.110.camel@localhost.localdomain> In-Reply-To: <1163968376.5826.110.camel@localhost.localdomain> Content-Type: text/plain; charset=us-ascii; format=flowed Cc: linuxppc-dev@ozlabs.org, Ingo Molnar , linux-kernel@vger.kernel.org, dwalker@mvista.com List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Hello. Benjamin Herrenschmidt wrote: >> I must not that this whole ack() vs eoi() stuff is misleading. For example, >>in 8259 driver, mask_ack() method actually sends EOI to PIC, not ACK's an IRQ >>-- the actual ACK is implicit on x86 and is used to read the interrupt vector >>form 8259 on PPC. So, IMO, there probably should only have been either ack() >>or eoi() method in the first place. Though I'm not familiar with ARM from >>which genirq stuff originated... > They are different concepts. Ack clears the event on the PIC, it's > tyically necessary for resetting the edge detection logic for edge > interrupts and has to happen before the handler is called. I know 8259. :-) It also resets the corresponding IRQ bit in IRR, and sets it in ISR where it's then cleared on EOI command. > On MPIC or XICS, this is implicit by reading the vector. On some more > dumb controllers, this has to be done explicitely. This is not implicit -- CPU has to read INTACK reg. on OpenPIC. Really implicit method is in action on x86 where CPU issues dual ACK bus cycle to get the vector form 8259... > EOI is a more "high level" thing that some "intelligent" PICs that > automatically raise the priority do to restore the priority to what it > was before the interrupt occured. Thank you, I know. Even 8259 has the notion of priority and EOI works the same way here. > Ben. WBR, Sergei