From 1278c9f87f1127b806a7733d3091df3ed2ab31c6 Mon Sep 17 00:00:00 2001 From: Sumit Semwal Date: Sat, 25 Mar 2017 21:48:07 +0530 Subject: PCI: Add comments about ROM BAR updating 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(+) (limited to 'drivers/pci') diff --git a/drivers/pci/rom.c b/drivers/pci/rom.c index eb0ad530dc43..3eea7fc5e1a2 100644 --- 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; diff --git a/drivers/pci/setup-res.c b/drivers/pci/setup-res.c index 674e76c9334e..d1ba5e0067c5 100644 --- a/drivers/pci/setup-res.c +++ b/drivers/pci/setup-res.c @@ -68,6 +68,12 @@ static void pci_std_update_resource(struct pci_dev *dev, int resno) 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; -- cgit v1.2.3