| Message ID | 20230201023803.660469-2-chenhuacai@loongson.cn (mailing list archive) |
|---|---|
| State | Superseded |
| Headers | show |
| Series | PCI: Resolve Loongson's LS7A PCI problems | expand |
On Wed, Feb 01, 2023 at 10:38:02AM +0800, Huacai Chen wrote: > This patch has a long story. Understatement of the year :) > @@ -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); Interesting. What I had in mind was keeping the original pcie_port_device_remove() unchanged, adding the new pcie_portdrv_shutdown(), and omitting pci_disable_device() just from pcie_portdrv_shutdown(). I haven't thought about the implications of omitting pci_disable_device() from the .remove() method (pcie_port_device_remove()). Just pointing this out quickly before going to bed in case you have a chance to think about what's the best strategy :) Bjorn
On Wed, Feb 1, 2023 at 11:42 AM Bjorn Helgaas <helgaas@kernel.org> wrote: > > On Wed, Feb 01, 2023 at 10:38:02AM +0800, Huacai Chen wrote: > > This patch has a long story. > > Understatement of the year :) > > > @@ -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); > > Interesting. What I had in mind was keeping the original > pcie_port_device_remove() unchanged, adding the new > pcie_portdrv_shutdown(), and omitting pci_disable_device() just from > pcie_portdrv_shutdown(). > > I haven't thought about the implications of omitting > pci_disable_device() from the .remove() method > (pcie_port_device_remove()). > > Just pointing this out quickly before going to bed in case you have a > chance to think about what's the best strategy :) Sorry that I misunderstood, V4 will be coming quickly. Huacai > > Bjorn
diff --git a/drivers/pci/pcie/portdrv.c b/drivers/pci/pcie/portdrv.c index 2cc2e60bcb39..9fe1fbca6476 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); } /**
This patch has a long story. 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 add a quirk to solve the LS7A problem but looks ugly. After long time discussions, Bjorn Helgaas suggest simply remove the pci_disable_device() in pcie_port_device_remove() and this patch do it exactly. [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@loongson.cn> --- drivers/pci/pcie/portdrv.c | 1 - 1 file changed, 1 deletion(-)