Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757008Ab3CSPiw (ORCPT ); Tue, 19 Mar 2013 11:38:52 -0400 Received: from netrider.rowland.org ([192.131.102.5]:56787 "HELO netrider.rowland.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with SMTP id S1756833Ab3CSPit (ORCPT ); Tue, 19 Mar 2013 11:38:49 -0400 Date: Tue, 19 Mar 2013 11:38:48 -0400 (EDT) From: Alan Stern X-X-Sender: stern@netrider.rowland.org To: Daniel Vetter cc: Chris Wilson , Jiri Kosina , Daniel Vetter , Greg KH , Harald Arnesen , Kernel development list , "Rafael J. Wysocki" , Peter Hurley , Thomas Meyer , Shawn Starr , USB list , , Bjorn Helgaas , , Yinghai Lu , Imre Deak , Daniel Kurtz , , Thomas Gleixner , "H. Peter Anvin" , , Arkadiusz Miskiewicz Subject: Re: gm45 intel gfx can generate non-MSI irq# in MSI mode (was Re: [PATCH] drm/i915: stop using GMBUS IRQs on Gen4 chips (was Re: [3.9-rc1] irq 16: nobody cared (was [3.9-rc1] very poor interrupt responses In-Reply-To: Message-ID: MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2735 Lines: 60 On Tue, 19 Mar 2013, Daniel Vetter wrote: > For reference below the updated commit message. > > Cheers, Daniel > > Author: Jiri Kosina > Date: Tue Mar 19 09:56:57 2013 +0100 > > drm/i915: stop using GMBUS IRQs on Gen4 chips > > Commit 28c70f162 ("drm/i915: use the gmbus irq for waits") switched to > using GMBUS irqs instead of GPIO bit-banging for chipset generations 4 > and above. > > It turns out though that on many systems this leads to spurious interrupts > being generated, long after the register write to disable the IRQs has been > issued. > > Typically this results in the spurious interrupt source getting > disabled: > > [ 9.636345] irq 16: nobody cared (try booting with the "irqpoll" option) > [ 9.637915] Pid: 4157, comm: ifup Tainted: GF > 3.9.0-rc2-00341-g0863702 #422 > [ 9.639484] Call Trace: > [ 9.640731] [] __report_bad_irq+0x1d/0xc7 > [ 9.640731] [] note_interrupt+0x15b/0x1e8 > [ 9.640731] [] handle_irq_event_percpu+0x1bf/0x214 > [ 9.640731] [] handle_irq_event+0x3c/0x5c > [ 9.640731] [] handle_fasteoi_irq+0x7a/0xb0 > [ 9.640731] [] handle_irq+0x1a/0x24 > [ 9.640731] [] do_IRQ+0x48/0xaf > [ 9.640731] [] common_interrupt+0x6a/0x6a > [ 9.640731] [] ? system_call_fastpath+0x16/0x1b > [ 9.640731] handlers: > [ 9.640731] [] usb_hcd_irq [usbcore] > [ 9.640731] [] yenta_interrupt [yenta_socket] > [ 9.640731] Disabling IRQ #16 > > The really curious thing is now that irq 16 is _not_ the interrupt for > the i915 driver when using MSI, but it _is_ the interrupt when not > using MSI. So by all indications it seems like gmbus is able to > generate a legacy (shared) interrupt in MSI mode on some > configurations. I've tried to reproduce this and the differentiating > thing seems to be that on unaffected systems no other device uses irq > 16 (which seems to be the non-MSI intel gfx interrupt on all gm45). That might be misleading. It's possible that the erroneous IRQs _are_ being issued but you're simply not aware of them. If the kernel thinks that no device is using IRQ 16 then it will leave that IRQ disabled. Alan Stern -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/