From mboxrd@z Thu Jan 1 00:00:00 1970 From: Andrew Morton Subject: Re: [PATCH 1/2] [PCI] Check that MWI bit really did get set Date: Sun, 15 Oct 2006 18:10:44 -0700 Message-ID: <20061015181044.ec414e4f.akpm@osdl.org> References: <1160161519800-git-send-email-matthew@wil.cx> <20061015191631.DE49D19FEC8@adsl-69-226-248-13.dsl.pltn13.pacbell.net> <20061015123432.4c6b7f15.akpm@osdl.org> <200610151545.59477.david-b@pacbell.net> <20061015161834.f96a0761.akpm@osdl.org> <1160956960.5732.99.camel@localhost.localdomain> <20061015164402.f9b8b4d2.akpm@osdl.org> <17714.54766.390707.532248@cargo.ozlabs.ibm.com> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Cc: Alan Cox , David Brownell , matthew@wil.cx, val_henson@linux.intel.com, netdev@vger.kernel.org, linux-pci@atrey.karlin.mff.cuni.cz, linux-kernel@vger.kernel.org, gregkh@suse.de Return-path: Received: from smtp.osdl.org ([65.172.181.4]:32203 "EHLO smtp.osdl.org") by vger.kernel.org with ESMTP id S1751191AbWJPBK6 (ORCPT ); Sun, 15 Oct 2006 21:10:58 -0400 To: Paul Mackerras In-Reply-To: <17714.54766.390707.532248@cargo.ozlabs.ibm.com> Sender: netdev-owner@vger.kernel.org List-Id: netdev.vger.kernel.org On Mon, 16 Oct 2006 10:44:30 +1000 Paul Mackerras wrote: > Andrew Morton writes: > > > Let me restore the words from my earlier email which you removed so that > > you could say that: > > > > For you the driver author to make assumptions about what's happening > > inside pci_set_mwi() is a layering violation. Maybe the bridge got > > hot-unplugged. Maybe the attempt to set MWI caused some synchronous PCI > > error. For example, take a look at the various implementations of > > pci_ops.read() around the place - various of them can fail for various > > reasons. > > Maybe aliens are firing a ray-gun at the card. I think it's > fundamentally wrong for the driver to deny service completely because > of a maybe. > > Either there was a transient error that only affected the attempt to > set MWI, in which case a printk (inside pci_set_mwi!) is appropriate, > and we carry on. Or there is a persistent error condition, in which > case the driver will see something else fail soon enough - something > that the driver actually needs to have working in order to operate - > and fail at that point. > > For the driver to stop and refuse to go any further because of an > error in pci_set_mwi has far more disadvantages than advantages. > Sure. So I think what we're needing in this case is: - A modified version of Willy's patch which returns 0 if MWI was enabled, 1 if MWI isn't available. - A printk if something went bad It appears that the various functions which try to match the line sizes already have printks if something went wrong, but they're using KERN_DEBUG facility level and that warning would dupliate the new one in pci_set_mwi(). And although the various implementations of pci_read_config_foo() and pci_write_config_foo() can return error codes, we have so many instances where we're not checking it, I don't think it's practical to try to start doing that everywhere. - drop the __must_check. Question is, should pci_set_mwi() ever return -EFOO? I guess it should, in the case where setting the line size didn't work out.