This is similar to commit 62b6dee1b44a ("PCI/portdrv: Prevent LS7A Bus Master clearing on shutdown"), which prevents LS7A Bus Master clearing on kexec.
The key point of this is to work around the LS7A defect that clearing PCI_COMMAND_MASTER prevents MMIO requests from going downstream, and we may need to do that even after .shutdown(), e.g., to print console messages. And in this case we rely on .shutdown() for the downstream devices to disable interrupts and DMA.
Only skip Bus Master clearing on bridges because endpoint devices still need it.
Cc: stable@vger.kernel.org Signed-off-by: Ming Wang wangming01@loongson.cn Signed-off-by: Huacai Chen chenhuacai@loongson.cn --- drivers/pci/pci-driver.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/drivers/pci/pci-driver.c b/drivers/pci/pci-driver.c index 602838416e6a..8a1e32367a06 100644 --- a/drivers/pci/pci-driver.c +++ b/drivers/pci/pci-driver.c @@ -517,7 +517,7 @@ static void pci_device_shutdown(struct device *dev) * 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)) + if (kexec_in_progress && !pci_is_bridge(pci_dev) && (pci_dev->current_state <= PCI_D3hot)) pci_clear_master(pci_dev); }
On Sun, May 11, 2025 at 04:34:13PM +0800, Huacai Chen wrote:
This is similar to commit 62b6dee1b44a ("PCI/portdrv: Prevent LS7A Bus Master clearing on shutdown"), which prevents LS7A Bus Master clearing on kexec.
So 62b6dee1b44a never worked as intented because the PCI core still cleared bus master bit?
The key point of this is to work around the LS7A defect that clearing PCI_COMMAND_MASTER prevents MMIO requests from going downstream, and we may need to do that even after .shutdown(), e.g., to print console messages. And in this case we rely on .shutdown() for the downstream devices to disable interrupts and DMA.
Only skip Bus Master clearing on bridges because endpoint devices still need it.
Cc: stable@vger.kernel.org Signed-off-by: Ming Wang wangming01@loongson.cn Signed-off-by: Huacai Chen chenhuacai@loongson.cn
drivers/pci/pci-driver.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/drivers/pci/pci-driver.c b/drivers/pci/pci-driver.c index 602838416e6a..8a1e32367a06 100644 --- a/drivers/pci/pci-driver.c +++ b/drivers/pci/pci-driver.c @@ -517,7 +517,7 @@ static void pci_device_shutdown(struct device *dev) * 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))
- if (kexec_in_progress && !pci_is_bridge(pci_dev) && (pci_dev->current_state <= PCI_D3hot))
I'm not a Kexec expert, but wouldn't not clearing the bus mastering for all PCI bridges safe? You are making a generic change for a defect in your hardware, so it might not apply to all other hardwares.
- Mani
Hi, Manivannan,
Sorry for the late reply.
On Fri, Jun 13, 2025 at 3:15 PM Manivannan Sadhasivam mani@kernel.org wrote:
On Sun, May 11, 2025 at 04:34:13PM +0800, Huacai Chen wrote:
This is similar to commit 62b6dee1b44a ("PCI/portdrv: Prevent LS7A Bus Master clearing on shutdown"), which prevents LS7A Bus Master clearing on kexec.
So 62b6dee1b44a never worked as intented because the PCI core still cleared bus master bit?
Commit 62b6dee1b44a only solved the poweroff/reboot problem, because in those cases kexec_in_progress is false and pci_clear_master() is skipped.
The key point of this is to work around the LS7A defect that clearing PCI_COMMAND_MASTER prevents MMIO requests from going downstream, and we may need to do that even after .shutdown(), e.g., to print console messages. And in this case we rely on .shutdown() for the downstream devices to disable interrupts and DMA.
Only skip Bus Master clearing on bridges because endpoint devices still need it.
Cc: stable@vger.kernel.org Signed-off-by: Ming Wang wangming01@loongson.cn Signed-off-by: Huacai Chen chenhuacai@loongson.cn
drivers/pci/pci-driver.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/drivers/pci/pci-driver.c b/drivers/pci/pci-driver.c index 602838416e6a..8a1e32367a06 100644 --- a/drivers/pci/pci-driver.c +++ b/drivers/pci/pci-driver.c @@ -517,7 +517,7 @@ static void pci_device_shutdown(struct device *dev) * 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))
if (kexec_in_progress && !pci_is_bridge(pci_dev) && (pci_dev->current_state <= PCI_D3hot))I'm not a Kexec expert, but wouldn't not clearing the bus mastering for all PCI bridges safe? You are making a generic change for a defect in your hardware, so it might not apply to all other hardwares.
I think most DMA comes from endpoint devices rather than bridges so kexec is probably safe. When I solve the problem in commit 62b6dee1b44a I want to make a special case for Loongson but Bjorn suggests doing a generic change, so I also do a generic change for kexec.
Huacai
- Mani
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