PCI: Add comments about ROM BAR updating (0b457dde) · Commits · 戴 / test

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 ("Ignore disabled ROM resources at setup") and ("[PATCH] Fix PCI ROM mapping"). Link: https://lkml.org/lkml/2005/8/30/138 Signed-off-by:

Bjorn Helgaas <bhelgaas@google.com> Reviewed-by:

Gavin Shan <gwshan@linux.vnet.ibm.com>

drivers/pci/rom.c

+5 −0

Original line number	Diff line number	Diff line
		@@ -35,6 +35,11 @@ int pci_enable_rom(struct pci_dev *pdev)
		if (res->flags & IORESOURCE_ROM_SHADOW)
		return 0;

		/*
		* 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, &region, res);
		pci_read_config_dword(pdev, pdev->rom_base_reg, &rom_addr);
		rom_addr &= ~PCI_ROM_ADDRESS_MASK;

drivers/pci/setup-res.c

+6 −0

Original line number	Diff line number	Diff line
		@@ -72,6 +72,12 @@ 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;

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