From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Subject: [PATCH 0/3] PCI: Fix detection of read-only BARs From: Myron Stowe To: bhelgaas@google.com, linux-pci@vger.kernel.org Cc: willy@linux.intel.com, unruh@physics.ubc.ca, linux-kernel@vger.kernel.org, martin@lucina.net Date: Thu, 30 Oct 2014 11:54:31 -0600 Message-ID: <20141030175430.22238.47671.stgit@amt.stowe> MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Sender: linux-kernel-owner@vger.kernel.org List-ID: While non-conformant, PCI devices having read-only (r/o) BARs - registers that when read return fixed, non-zero, values regardless of whether or not their being sized - occasionally turn up. Pre-git commit 1307ef662199 [1] was the initial attempt to detect such BARs. The detection mechanism used however ended up exposing further unexpected behaviors on enough devices that it had to be reverted [2]. A subsequent solution, which is still currently in use, was put in place with pre-git commit 2c79a80ab7b7 ("[PCI] Correctly size hardwired empty BARs"). This solution's logic detects r/o BARs via the following (see 'pci_size()'): /* base == maxbase can be valid only if the BAR has already been programmed with all 1s. */ if (base == maxbase && ((base | size) & mask) != mask) return 0; Later, commit 6ac665c63dca ("PCI: rewrite PCI BAR reading code") was introduced, re-factoring PCI's core BAR sizing logic. The commit altered __pci_read_base's local variable 'l', stripping off its lower, non-addressing related bits, prior to being passed in as the 'base' parameter to pci_size(). This masking broke the r/o BAR detection logic's first comparison check for r/o BARs that have any of their lower order bits, bits that are not part of a BARs "base address" field, set. For such cases, the 'base == maxbase' comparison check will no longer ever be "true". This series restores the r/o BAR detection logic so that it will once again catch, and ignore, such occurrences as have been encountered to date: - AGP aperture BAR of AMD-7xx host bridges; if the AGP window disabled, this BAR is read-only and read as 0x00000008 [1] - BAR0-4 of ALi IDE controllers can be non-zero and read-only [1] - Intel Sandy Bridge - Thermal Management Controller [8086:0103]; BAR 0 returning 0xfed98004 [3] - Intel Xeon E5 v3/Core i7 Power Control Unit [8086:2fc0]; Bar 0 returning 0x00001a [4] [1] From Thomas Gleixner's "Linux kernel history" repository: https://git.kernel.org/cgit/linux/kernel/git/tglx/history.git/commit/drivers/pci/probe.c?id=1307ef6621991f1c4bc3cec1b5a4ebd6fd3d66b9 pre-git commit 1307ef662199 "PCI: probing read-only Bars" [2] Pre-git commit 182d090b9dfe "Undo due to weird behaviour on various boxes" [3] https://bugzilla.kernel.org/show_bug.cgi?id=43331 [4] https://bugzilla.kernel.org/show_bug.cgi?id=85991 Myron Stowe (3): PCI: Restore detection of read-only BARs PCI: Re-factor __pci_read_base PCI: Add a informational printk for invalid BARs drivers/pci/probe.c | 75 +++++++++++++++++++++++---------------------------- 1 file changed, 34 insertions(+), 41 deletions(-) --