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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] <chain broken>

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Acked-by: Bjorn Helgaas <bhelgaas@google.com>
Signed-off-by: Jason Cooper <jason@lakedaemon.net>
This commit is contained in:
Thomas Petazzoni 2013-05-23 16:32:53 +02:00 committed by Jason Cooper
parent 197fc226d9
commit 6eb237c41a
1 changed files with 1 additions and 4 deletions
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5
drivers/pci/host/pci-mvebu.c
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@ -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(struct mvebu_pcie_port *port)
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(struct mvebu_pcie_port *port,
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(struct mvebu_pcie_port *port,
switch (where & ~3) {
case PCI_COMMAND:
bridge->command = value & 0xffff;
bridge->status = value >> 16;
break;
case PCI_BASE_ADDRESS_0 ... PCI_BASE_ADDRESS_1: