From 370c8181fd848948aeae371bbc1124dc0dead22b Mon Sep 17 00:00:00 2001 From: Thomas Petazzoni Date: Thu, 23 May 2013 16:32:53 +0200 Subject: [PATCH 19/29] pci: mvebu: fix the emulation of the status register The status register of the PCI configuration space of PCI-to-PCI bridges contain some read-only bits, and so write-1-to-clear bits. So, the Linux PCI core sometimes writes 0xffff to this status register, and in the current PCI-to-PCI bridge emulation code of the Marvell driver, we do take all those 1s being written. Even the read-only bits are being overwritten. For now, all the read-only bits should be emulated to have the zero value. The other bits, that are write-1-to-clear bits are used to report various kind of errors, and are never set by the emulated bridge, so there is no need to support this write-1-to-clear bits mechanism. As a conclusion, the easiest solution is to simply emulate this status register by returning zero when read, and ignore the writes to it. This has two visible effects: * The devsel is no longer 'unknown' in, i.e Flags: bus master, 66MHz, user-definable features, ?? devsel, latency 0 becomes: Flags: bus master, 66MHz, user-definable features, fast devsel, latency 0 in lspci -v. This was caused by a value of 11b being read for devsel, which is an invalid value. This 11b value being read was due to a previous write of 0xffff into the status register. * The capability list is no longer broken, because we indicate to the Linux PCI core that we don't have a Capabilities Pointer in the PCI configuration space of this bridge. The following message is therefore no longer visible in lspci -v: Capabilities: [fc] Signed-off-by: Thomas Petazzoni Acked-by: Bjorn Helgaas Signed-off-by: Jason Cooper --- drivers/pci/host/pci-mvebu.c | 5 +---- 1 file changed, 1 insertion(+), 4 deletions(-) --- a/drivers/pci/host/pci-mvebu.c +++ b/drivers/pci/host/pci-mvebu.c @@ -69,7 +69,6 @@ struct mvebu_sw_pci_bridge { u16 vendor; u16 device; u16 command; - u16 status; u16 class; u8 interface; u8 revision; @@ -359,7 +358,6 @@ static void mvebu_sw_pci_bridge_init(str memset(bridge, 0, sizeof(struct mvebu_sw_pci_bridge)); - bridge->status = PCI_STATUS_CAP_LIST; bridge->class = PCI_CLASS_BRIDGE_PCI; bridge->vendor = PCI_VENDOR_ID_MARVELL; bridge->device = MARVELL_EMULATED_PCI_PCI_BRIDGE_ID; @@ -386,7 +384,7 @@ static int mvebu_sw_pci_bridge_read(stru break; case PCI_COMMAND: - *value = bridge->status << 16 | bridge->command; + *value = bridge->command; break; case PCI_CLASS_REVISION: @@ -479,7 +477,6 @@ static int mvebu_sw_pci_bridge_write(str switch (where & ~3) { case PCI_COMMAND: bridge->command = value & 0xffff; - bridge->status = value >> 16; break; case PCI_BASE_ADDRESS_0 ... PCI_BASE_ADDRESS_1: