[RFC PATCH v2] PCI/portdrv: Only disable Bus Master on kexec reboot and connected PCI devices

[Tiezhu Yang <yangtiezhu@loongson.cn>]

After commit 745be2e700cd ("PCIe: portdrv: call pci_disable_device
during remove") and commit cc27b735ad3a ("PCI/portdrv: Turn off PCIe
services during shutdown"), it also calls pci_disable_device() during
shutdown, this leads to shutdown or reboot failure occasionally due to
clear PCI_COMMAND_MASTER on the device in do_pci_disable_device().

drivers/pci/pci.c
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.

As Oliver O'Halloran said, no need to call pci_disable_device() when
actually shutting down, but we should call pci_disable_device() before
handing over to the new kernel on kexec reboot, so we can do some
condition checks which are similar with pci_device_shutdown(), this is
done by commit 4fc9bbf98fd6 ("PCI: Disable Bus Master only on kexec
reboot") and commit 6e0eda3c3898 ("PCI: Don't try to disable Bus Master
on disconnected PCI devices").

drivers/pci/pci-driver.c
static void pci_device_shutdown(struct device *dev)
{
...

        /*
         * If this is a kexec reboot, turn off Bus Master bit on the
         * device to tell it to not continue to do DMA. Don't touch
         * devices in D3cold or unknown states.
         * If it is not a kexec reboot, firmware will hit the PCI
         * devices with big hammer and stop their DMA any way.
         */
        if (kexec_in_progress && (pci_dev->current_state <= PCI_D3hot))
                pci_clear_master(pci_dev);
}

Signed-off-by: Tiezhu Yang <yangtiezhu@loongson.cn>
---
 drivers/pci/pcie/portdrv_core.c |  1 -
 drivers/pci/pcie/portdrv_pci.c  | 25 ++++++++++++++++++++++++-
 2 files changed, 24 insertions(+), 2 deletions(-)

diff --git a/drivers/pci/pcie/portdrv_core.c b/drivers/pci/pcie/portdrv_core.c
index 50a9522..1991aca 100644
--- a/drivers/pci/pcie/portdrv_core.c
+++ b/drivers/pci/pcie/portdrv_core.c
@@ -491,7 +491,6 @@ 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);
 }
 
 /**
diff --git a/drivers/pci/pcie/portdrv_pci.c b/drivers/pci/pcie/portdrv_pci.c
index 3a3ce40..ce89a9e8 100644
--- a/drivers/pci/pcie/portdrv_pci.c
+++ b/drivers/pci/pcie/portdrv_pci.c
@@ -15,6 +15,7 @@
 #include <linux/init.h>
 #include <linux/aer.h>
 #include <linux/dmi.h>
+#include <linux/kexec.h>
 
 #include "../pci.h"
 #include "portdrv.h"
@@ -143,6 +144,28 @@ 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)
+{
+	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 this is a kexec reboot, turn off Bus Master bit on the
+	 * device to tell it to not continue to do DMA. Don't touch
+	 * devices in D3cold or unknown states.
+	 * If it is not a kexec reboot, firmware will hit the PCI
+	 * devices with big hammer and stop their DMA any way.
+	 */
+	if (kexec_in_progress && (dev->current_state <= PCI_D3hot))
+		pci_disable_device(dev);
 }
 
 static pci_ers_result_t pcie_portdrv_error_detected(struct pci_dev *dev,
@@ -211,7 +234,7 @@ static void pcie_portdrv_err_resume(struct pci_dev *dev)
 
 	.probe		= pcie_portdrv_probe,
 	.remove		= pcie_portdrv_remove,
-	.shutdown	= pcie_portdrv_remove,
+	.shutdown	= pcie_portdrv_shutdown,
 
 	.err_handler	= &pcie_portdrv_err_handler,
 
-- 
1.8.3.1