Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753602AbdC1Mfn (ORCPT ); Tue, 28 Mar 2017 08:35:43 -0400 Received: from mail.linuxfoundation.org ([140.211.169.12]:59174 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752657AbdC1Mfh (ORCPT ); Tue, 28 Mar 2017 08:35:37 -0400 From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org, stable@vger.kernel.org Cc: Greg Kroah-Hartman , Bjorn Helgaas , Gavin Shan , Sasha Levin , Sumit Semwal Subject: [PATCH 4.4 62/76] PCI: Add comments about ROM BAR updating Date: Tue, 28 Mar 2017 14:30:59 +0200 Message-Id: <20170328122602.470293133@linuxfoundation.org> X-Mailer: git-send-email 2.12.1 In-Reply-To: <20170328122559.966310440@linuxfoundation.org> References: <20170328122559.966310440@linuxfoundation.org> User-Agent: quilt/0.65 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2548 Lines: 70 4.4-stable review patch. If anyone has any objections, please let me know. ------------------ From: Sumit Semwal From: Bjorn Helgaas [ Upstream commit 0b457dde3cf8b7c76a60f8e960f21bbd4abdc416 ] pci_update_resource() updates a hardware BAR so its address matches the kernel's struct resource UNLESS it's a disabled ROM BAR. We only update those when we enable the ROM. It's not obvious from the code why ROM BARs should be handled specially. Apparently there are Matrox devices with defective ROM BARs that read as zero when disabled. That means that if pci_enable_rom() reads the disabled BAR, sets PCI_ROM_ADDRESS_ENABLE (without re-inserting the address), and writes it back, it would enable the ROM at address zero. Add comments and references to explain why we can't make the code look more rational. The code changes are from 755528c860b0 ("Ignore disabled ROM resources at setup") and 8085ce084c0f ("[PATCH] Fix PCI ROM mapping"). Link: https://lkml.org/lkml/2005/8/30/138 Signed-off-by: Bjorn Helgaas Reviewed-by: Gavin Shan Signed-off-by: Sasha Levin Signed-off-by: Greg Kroah-Hartman [sumits: minor fixup in rom.c for 4.4.y] Signed-off-by: Sumit Semwal Signed-off-by: Greg Kroah-Hartman --- drivers/pci/rom.c | 5 +++++ drivers/pci/setup-res.c | 6 ++++++ 2 files changed, 11 insertions(+) --- a/drivers/pci/rom.c +++ b/drivers/pci/rom.c @@ -31,6 +31,11 @@ int pci_enable_rom(struct pci_dev *pdev) if (!res->flags) return -1; + /* + * Ideally pci_update_resource() would update the ROM BAR address, + * and we would only set the enable bit here. But apparently some + * devices have buggy ROM BARs that read as zero when disabled. + */ pcibios_resource_to_bus(pdev->bus, ®ion, res); pci_read_config_dword(pdev, pdev->rom_base_reg, &rom_addr); rom_addr &= ~PCI_ROM_ADDRESS_MASK; --- a/drivers/pci/setup-res.c +++ b/drivers/pci/setup-res.c @@ -68,6 +68,12 @@ static void pci_std_update_resource(stru if (resno < PCI_ROM_RESOURCE) { reg = PCI_BASE_ADDRESS_0 + 4 * resno; } else if (resno == PCI_ROM_RESOURCE) { + + /* + * Apparently some Matrox devices have ROM BARs that read + * as zero when disabled, so don't update ROM BARs unless + * they're enabled. See https://lkml.org/lkml/2005/8/30/138. + */ if (!(res->flags & IORESOURCE_ROM_ENABLE)) return;