[PATCH RFC v2 03/21] PCI: hotplug: Add a flag for the movable BARs feature

[Sergey Miroshnichenko <s.miroshnichenko@yadro.com>]

If a new PCIe device has been hot-plugged between the two active ones
without big enough gap between their BARs, these BARs should be moved
if their drivers support this feature. The drivers should be notified
and paused during the procedure:

1)                 dev 8 (new)
                       |
                       v
.. |  dev 3  |  dev 3  |  dev 5  |  dev 7  |
.. |  BAR 0  |  BAR 1  |  BAR 0  |  BAR 0  |

2)                             dev 8
                                 |
                                 v
.. |  dev 3  |  dev 3  | -->           --> |  dev 5  |  dev 7  |
.. |  BAR 0  |  BAR 1  | -->           --> |  BAR 0  |  BAR 0  |

 3)

.. |  dev 3  |  dev 3  |  dev 8  |  dev 8  |  dev 5  |  dev 7  |
.. |  BAR 0  |  BAR 1  |  BAR 0  |  BAR 1  |  BAR 0  |  BAR 0  |

Thus, prior reservation of memory regions by BIOS/bootloader/firmware
is not required anymore for the PCIe hotplug.

The PCI_MOVABLE_BARS flag is set by the platform is this feature is
supported and tested, but can be overridden by the following command
line option:
    pcie_movable_bars={ off | force }

Signed-off-by: Sergey Miroshnichenko <s.miroshnichenko@yadro.com>
---
 .../admin-guide/kernel-parameters.txt         |  7 ++++++
 drivers/pci/pci.c                             | 24 +++++++++++++++++++
 include/linux/pci.h                           |  2 ++
 3 files changed, 33 insertions(+)

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index b799bcf67d7b..2165c4b5aea6 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -3387,6 +3387,13 @@
 		nomsi	Do not use MSI for native PCIe PME signaling (this makes
 			all PCIe root ports use INTx for all services).
 
+	pcie_movable_bars=[PCIE]
+			Override the movable BARs support detection:
+		off
+			Disable even if supported by the platform
+		force
+			Enable even if not explicitly declared as supported
+
 	pcmv=		[HW,PCMCIA] BadgePAD 4
 
 	pd_ignore_unused
diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
index 5580ddc5b9b1..71e056771e67 100644
--- a/drivers/pci/pci.c
+++ b/drivers/pci/pci.c
@@ -139,6 +139,30 @@ static int __init pcie_port_pm_setup(char *str)
 }
 __setup("pcie_port_pm=", pcie_port_pm_setup);
 
+static bool pcie_movable_bars_off;
+static bool pcie_movable_bars_force;
+static int __init pcie_movable_bars_setup(char *str)
+{
+	if (!strcmp(str, "off"))
+		pcie_movable_bars_off = true;
+	else if (!strcmp(str, "force"))
+		pcie_movable_bars_force = true;
+	return 1;
+}
+__setup("pcie_movable_bars=", pcie_movable_bars_setup);
+
+bool pci_movable_bars_enabled(void)
+{
+	if (pcie_movable_bars_off)
+		return false;
+
+	if (pcie_movable_bars_force)
+		return true;
+
+	return pci_has_flag(PCI_MOVABLE_BARS);
+}
+EXPORT_SYMBOL(pci_movable_bars_enabled);
+
 /* Time to wait after a reset for device to become responsive */
 #define PCIE_RESET_READY_POLL_MS 60000
 
diff --git a/include/linux/pci.h b/include/linux/pci.h
index 65f1d8c2f082..84751f0931cd 100644
--- a/include/linux/pci.h
+++ b/include/linux/pci.h
@@ -862,6 +862,7 @@ enum {
 	PCI_ENABLE_PROC_DOMAINS	= 0x00000010,	/* Enable domains in /proc */
 	PCI_COMPAT_DOMAIN_0	= 0x00000020,	/* ... except domain 0 */
 	PCI_SCAN_ALL_PCIE_DEVS	= 0x00000040,	/* Scan all, not just dev 0 */
+	PCI_MOVABLE_BARS	= 0x00000080,	/* Runtime BAR reassign after hotplug */
 };
 
 /* These external functions are only available when PCI support is enabled */
@@ -1341,6 +1342,7 @@ unsigned char pci_bus_max_busnr(struct pci_bus *bus);
 void pci_setup_bridge(struct pci_bus *bus);
 resource_size_t pcibios_window_alignment(struct pci_bus *bus,
 					 unsigned long type);
+bool pci_movable_bars_enabled(void);
 
 #define PCI_VGA_STATE_CHANGE_BRIDGE (1 << 0)
 #define PCI_VGA_STATE_CHANGE_DECODES (1 << 1)
-- 
2.20.1