[PATCH V4 1/4] PCI/portdrv: Don't disable device during shutdown

[Huacai Chen <chenhuacai@loongson.cn>]

Use separate remove()/shutdown() callback, and don't disable PCI device
during shutdown. This can avoid some poweroff/reboot failures.

The poweroff/reboot failures could easily be reproduced on Loongson
platforms. I think this is not a Loongson-specific problem, instead, is
a problem related to some specific PCI hosts. On some x86 platforms,
radeon/amdgpu devices can cause the same problem [1][2], and commit
faefba95c9e8ca3a ("drm/amdgpu: just suspend the hw on pci shutdown")
can resolve it.

As Tiezhu said, this occasionally shutdown or reboot failure is due to
clear PCI_COMMAND_MASTER on the device in do_pci_disable_device() [3].

static void do_pci_disable_device(struct pci_dev *dev)
{
        u16 pci_command;

        pci_read_config_word(dev, PCI_COMMAND, &pci_command);
        if (pci_command & PCI_COMMAND_MASTER) {
                pci_command &= ~PCI_COMMAND_MASTER;
                pci_write_config_word(dev, PCI_COMMAND, pci_command);
        }

        pcibios_disable_device(dev);
}

When remove "pci_command &= ~PCI_COMMAND_MASTER;", it can work well when
shutdown or reboot. The root cause on Loongson platform 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 doesn't send TIMEOUT to CPU,
which causes CPU wait forever (hardware deadlock). This behavior is a
PCIe protocol violation, and will be fixed in new revisions of hardware
(add timeout mechanism for CPU read request, whether or not Bus Master
bit is cleared).

Radeon driver is more difficult than amdgpu due to its confusing symbol
names, and I have maintained an out-of-tree patch for a long time [4].
Recently, we found more and more devices can cause the same problem, and
it is very difficult to modify all problematic drivers as radeon/amdgpu
does (the .shutdown callback should make sure there is no DMA activity).
So, I think modify the PCIe port driver is a simple and effective way.
Because there is no poweroff/reboot problems before cc27b735ad3a75574a6a
("PCI/portdrv: Turn off PCIe services during shutdown"). And as early
discussed, kexec can still work fine after this patch [5].

[1] https://bugs.freedesktop.org/show_bug.cgi?id=97980
[2] https://bugs.freedesktop.org/show_bug.cgi?id=98638
[3] https://lore.kernel.org/patchwork/patch/1305067/
[4] https://github.com/chenhuacai/linux/commit/8da06f9b669831829416a3e9f4d1c57f217a42f0
[5] http://patchwork.ozlabs.org/project/linux-pci/patch/1600680138-10949-1-git-send-email-chenhc@lemote.com/

Cc: Sinan Kaya <okaya@kernel.org>
Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>
Signed-off-by: Tiezhu Yang <yangtiezhu@loongson.cn>
---
 drivers/pci/pcie/portdrv.h      |  2 +-
 drivers/pci/pcie/portdrv_core.c |  6 ++++--
 drivers/pci/pcie/portdrv_pci.c  | 15 +++++++++++++--
 3 files changed, 18 insertions(+), 5 deletions(-)

diff --git a/drivers/pci/pcie/portdrv.h b/drivers/pci/pcie/portdrv.h
index 2ff5724b8f13..358d7281f6e8 100644
--- a/drivers/pci/pcie/portdrv.h
+++ b/drivers/pci/pcie/portdrv.h
@@ -117,7 +117,7 @@ int pcie_port_device_resume(struct device *dev);
 int pcie_port_device_runtime_suspend(struct device *dev);
 int pcie_port_device_runtime_resume(struct device *dev);
 #endif
-void pcie_port_device_remove(struct pci_dev *dev);
+void pcie_port_device_remove(struct pci_dev *dev, bool disable);
 int __must_check pcie_port_bus_register(void);
 void pcie_port_bus_unregister(void);
 
diff --git a/drivers/pci/pcie/portdrv_core.c b/drivers/pci/pcie/portdrv_core.c
index e1fed6649c41..98c0a99a41d6 100644
--- a/drivers/pci/pcie/portdrv_core.c
+++ b/drivers/pci/pcie/portdrv_core.c
@@ -484,11 +484,13 @@ EXPORT_SYMBOL_GPL(pcie_port_find_device);
  * Remove PCI Express port service devices associated with given port and
  * disable MSI-X or MSI for the port.
  */
-void pcie_port_device_remove(struct pci_dev *dev)
+void pcie_port_device_remove(struct pci_dev *dev, bool disable)
 {
 	device_for_each_child(&dev->dev, NULL, remove_iter);
 	pci_free_irq_vectors(dev);
-	pci_disable_device(dev);
+
+	if (disable)
+		pci_disable_device(dev);
 }
 
 /**
diff --git a/drivers/pci/pcie/portdrv_pci.c b/drivers/pci/pcie/portdrv_pci.c
index c7ff1eea225a..562fbf3c1ea9 100644
--- a/drivers/pci/pcie/portdrv_pci.c
+++ b/drivers/pci/pcie/portdrv_pci.c
@@ -147,7 +147,18 @@ static void pcie_portdrv_remove(struct pci_dev *dev)
 		pm_runtime_dont_use_autosuspend(&dev->dev);
 	}
 
-	pcie_port_device_remove(dev);
+	pcie_port_device_remove(dev, true);
+}
+
+static void pcie_portdrv_shutdown(struct pci_dev *dev)
+{
+	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, false);
 }
 
 static pci_ers_result_t pcie_portdrv_error_detected(struct pci_dev *dev,
@@ -219,7 +230,7 @@ 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,
 
-- 
2.27.0