Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755899Ab3JCWwB (ORCPT ); Thu, 3 Oct 2013 18:52:01 -0400 Received: from webmail.solarflare.com ([12.187.104.25]:29054 "EHLO webmail.solarflare.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755349Ab3JCWv6 (ORCPT ); Thu, 3 Oct 2013 18:51:58 -0400 Message-ID: <1380840585.3419.50.camel@bwh-desktop.uk.level5networks.com> Subject: Re: [PATCH RFC 00/77] Re-design MSI/MSI-X interrupts enablement pattern From: Ben Hutchings To: Alexander Gordeev CC: , Bjorn Helgaas , "Ralf Baechle" , Michael Ellerman , Benjamin Herrenschmidt , Martin Schwidefsky , Ingo Molnar , Tejun Heo , Dan Williams , Andy King , Jon Mason , Matt Porter , , , , , , , , , , , , , , Solarflare linux maintainers , "VMware, Inc." , In-Reply-To: References: Organization: Solarflare Content-Type: text/plain; charset="UTF-8" Date: Thu, 3 Oct 2013 23:49:45 +0100 MIME-Version: 1.0 X-Mailer: Evolution 3.6.4 (3.6.4-3.fc18) Content-Transfer-Encoding: 7bit X-Originating-IP: [10.17.20.137] X-TM-AS-Product-Ver: SMEX-10.0.0.1412-7.000.1014-20192.004 X-TM-AS-Result: No--21.602200-0.000000-31 X-TM-AS-User-Approved-Sender: Yes X-TM-AS-User-Blocked-Sender: No Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2386 Lines: 61 On Wed, 2013-10-02 at 12:48 +0200, Alexander Gordeev wrote: > This series is against "next" branch in Bjorn's repo: > git://git.kernel.org/pub/scm/linux/kernel/git/helgaas/pci.git > > Currently pci_enable_msi_block() and pci_enable_msix() interfaces > return a error code in case of failure, 0 in case of success and a > positive value which indicates the number of MSI-X/MSI interrupts > that could have been allocated. The latter value should be passed > to a repeated call to the interfaces until a failure or success: > > > for (i = 0; i < FOO_DRIVER_MAXIMUM_NVEC; i++) > adapter->msix_entries[i].entry = i; > > while (nvec >= FOO_DRIVER_MINIMUM_NVEC) { > rc = pci_enable_msix(adapter->pdev, > adapter->msix_entries, nvec); > if (rc > 0) > nvec = rc; > else > return rc; > } > > return -ENOSPC; > > > This technique proved to be confusing and error-prone. Vast share > of device drivers simply fail to follow the described guidelines. > > This update converts pci_enable_msix() and pci_enable_msi_block() > interfaces to canonical kernel functions and makes them return a > error code in case of failure or 0 in case of success. [...] I think this is fundamentally flawed: pci_msix_table_size() and pci_get_msi_cap() can only report the limits of the *device* (which the driver usually already knows), whereas MSI allocation can also be constrained due to *global* limits on the number of distinct IRQs. Currently pci_enable_msix() will report a positive value if it fails due to the global limit. Your patch 7 removes that. pci_enable_msi_block() unfortunately doesn't appear to do this. It seems to me that a more useful interface would take a minimum and maximum number of vectors from the driver. This wouldn't allow the driver to specify that it could only accept, say, any even number within a certain range, but you could still leave the current functions available for any driver that needs that. Ben. -- Ben Hutchings, Staff Engineer, Solarflare Not speaking for my employer; that's the marketing department's job. They asked us to note that Solarflare product names are trademarked. -- 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/