After cc27b735ad3a7557 ("PCI/portdrv: Turn off PCIe services during
shutdown") we observe poweroff/reboot failures on systems with LS7A
chipset.
We found that if we remove "pci_command &= ~PCI_COMMAND_MASTER" in
do_pci_disable_device(), it can work well. The hardware engineer says
that the root cause is that CPU is still accessing PCIe devices while
poweroff/reboot, and if we disable the Bus Master Bit at this time, the
PCIe controller doesn't forward requests to downstream devices, and also
does not send TIMEOUT to CPU, which causes CPU wait forever (hardware
deadlock).
To be clear, the sequence is like this:
- CPU issues MMIO read to device below Root Port
- LS7A Root Port fails to forward transaction to secondary bus
because of LS7A Bus Master defect
- CPU hangs waiting for response to MMIO read
Then how is userspace able to use a device after the device is removed?
To give more details, let's take the graphics driver (e.g. amdgpu) as
an example. The userspace programs call printf() to display "shutting
down xxx service" during shutdown/reboot, or the kernel calls printk()
to display something during shutdown/reboot. These can happen at any
time, even after we call pcie_port_device_remove() to disable the pcie
port on the graphic card.
The call stack is: printk() --> call_console_drivers() --> con->write()
--> vt_console_print() --> fbcon_putcs()
This scenario happens because userspace programs (or the kernel itself)
don't know whether a device is 'usable', they just use it, at any time.
This hardware behavior is a PCIe protocol violation (Bus Master should
not be involved in CPU MMIO transactions), and it will be fixed in new
revisions of hardware (add timeout mechanism for CPU read request,
whether or not Bus Master bit is cleared).
On some x86 platforms, radeon/amdgpu devices can cause similar problems
[1][2]. Once before I wanted to make a single patch to solve "all of
these problems" together, but it seems unreasonable because maybe they
are not exactly the same problem. So, this patch add a new function
pcie_portdrv_shutdown(), a slight modified copy of pcie_portdrv_remove()
dedicated for the shutdown path, and then add a quirk just for LS7A to
avoid clearing Bus Master bit in pcie_portdrv_shutdown(). Leave other
platforms behave as before.
[1] https://bugs.freedesktop.org/show_bug.cgi?id=97980
[2] https://bugs.freedesktop.org/show_bug.cgi?id=98638
Signed-off-by: Huacai Chen <chenhuacai@xxxxxxxxxxx>
---
drivers/pci/controller/pci-loongson.c | 17 +++++++++++++++++
drivers/pci/pcie/portdrv.c | 21 +++++++++++++++++++--
include/linux/pci.h | 1 +
3 files changed, 37 insertions(+), 2 deletions(-)
diff --git a/drivers/pci/controller/pci-loongson.c b/drivers/pci/controller/pci-loongson.c
index 759ec211c17b..641308ba4126 100644
--- a/drivers/pci/controller/pci-loongson.c
+++ b/drivers/pci/controller/pci-loongson.c
@@ -93,6 +93,24 @@ DECLARE_PCI_FIXUP_EARLY(PCI_VENDOR_ID_LOONGSON,
DECLARE_PCI_FIXUP_EARLY(PCI_VENDOR_ID_LOONGSON,
DEV_PCIE_PORT_2, loongson_mrrs_quirk);
+static void loongson_bmaster_quirk(struct pci_dev *pdev)
+{
+ /*
+ * Some Loongson PCIe ports will cause CPU deadlock if there is
+ * MMIO access to a downstream device when the root port disable
+ * the Bus Master bit during poweroff/reboot.
+ */
+ struct pci_host_bridge *bridge = pci_find_host_bridge(pdev->bus);
+
+ bridge->no_dis_bmaster = 1;
+}
+DECLARE_PCI_FIXUP_EARLY(PCI_VENDOR_ID_LOONGSON,
+ DEV_PCIE_PORT_0, loongson_bmaster_quirk);
+DECLARE_PCI_FIXUP_EARLY(PCI_VENDOR_ID_LOONGSON,
+ DEV_PCIE_PORT_1, loongson_bmaster_quirk);
+DECLARE_PCI_FIXUP_EARLY(PCI_VENDOR_ID_LOONGSON,
+ DEV_PCIE_PORT_2, loongson_bmaster_quirk);
+
static void loongson_pci_pin_quirk(struct pci_dev *pdev)
{
pdev->pin = 1 + (PCI_FUNC(pdev->devfn) & 3);
diff --git a/drivers/pci/pcie/portdrv.c b/drivers/pci/pcie/portdrv.c
index 2cc2e60bcb39..96f45c444422 100644
--- a/drivers/pci/pcie/portdrv.c
+++ b/drivers/pci/pcie/portdrv.c
@@ -501,7 +501,6 @@ static void pcie_port_device_remove(struct pci_dev *dev)
{
device_for_each_child(&dev->dev, NULL, remove_iter);
pci_free_irq_vectors(dev);
- pci_disable_device(dev);
}
/**
@@ -727,6 +726,24 @@ static void pcie_portdrv_remove(struct pci_dev *dev)
}
pcie_port_device_remove(dev);
+
+ pci_disable_device(dev);
+}
+
+static void pcie_portdrv_shutdown(struct pci_dev *dev)
+{
+ struct pci_host_bridge *bridge = pci_find_host_bridge(dev->bus);
+
+ if (pci_bridge_d3_possible(dev)) {
+ pm_runtime_forbid(&dev->dev);
+ pm_runtime_get_noresume(&dev->dev);
+ pm_runtime_dont_use_autosuspend(&dev->dev);
+ }
+
+ pcie_port_device_remove(dev);
+
+ if (!bridge->no_dis_bmaster)
+ pci_disable_device(dev);
}
static pci_ers_result_t pcie_portdrv_error_detected(struct pci_dev *dev,
@@ -777,7 +794,7 @@ static struct pci_driver pcie_portdriver = {
.probe = pcie_portdrv_probe,
.remove = pcie_portdrv_remove,
- .shutdown = pcie_portdrv_remove,
+ .shutdown = pcie_portdrv_shutdown,
.err_handler = &pcie_portdrv_err_handler,
diff --git a/include/linux/pci.h b/include/linux/pci.h
index 3df2049ec4a8..a64dbcb89231 100644
--- a/include/linux/pci.h
+++ b/include/linux/pci.h
@@ -573,6 +573,7 @@ struct pci_host_bridge {
unsigned int ignore_reset_delay:1; /* For entire hierarchy */
unsigned int no_ext_tags:1; /* No Extended Tags */
unsigned int no_inc_mrrs:1; /* No Increase MRRS */
+ unsigned int no_dis_bmaster:1; /* No Disable Bus Master */
unsigned int native_aer:1; /* OS may use PCIe AER */
unsigned int native_pcie_hotplug:1; /* OS may use PCIe hotplug */
unsigned int native_shpc_hotplug:1; /* OS may use SHPC hotplug */
--
2.31.1
