Re: [PATCH v3 1/2] PCI: pciehp: Add support for async hotplug with native AER and DPC/EDR
From: Sathyanarayanan Kuppuswamy
Date: Thu Jun 22 2023 - 19:22:57 EST
On 6/21/23 11:51 AM, Smita Koralahalli wrote:
> According to Section 6.7.6 of PCIe Base Specification [1], async removal
> with DPC may result in surprise down error. This error is expected and
> is just a side-effect of async remove.
>
> Add support to handle the surprise down error generated as a side-effect
> of async remove. Typically, this error is benign as the pciehp handler
> invoked by PDC or/and DLLSC alongside DPC, de-enumerates and brings down
> the device appropriately. But the error messages might confuse users. Get
> rid of these irritating log messages with a 1s delay while pciehp waits
> for dpc recovery.
>
> The implementation is as follows: On an async remove a DPC is triggered
> along with a Presence Detect State change and/or DLL State Change.
> Determine it's an async remove by checking for DPC Trigger Status in DPC
> Status Register and Surprise Down Error Status in AER Uncorrected Error
> Status to be non-zero. If true, treat the DPC event as a side-effect of
> async remove, clear the error status registers and continue with hot-plug
> tear down routines. If not, follow the existing routine to handle AER and
> DPC errors.
>
> Please note that, masking Surprise Down Errors was explored as an
> alternative approach, but left due to the odd behavior that masking only
> avoids the interrupt, but still records an error per PCIe r6.0.1 Section
> 6.2.3.2.2. That stale error is going to be reported the next time some
> error other than Surprise Down is handled.
I think this fix is applicable to the EDR code path as well.
>
> Dmesg before:
>
> pcieport 0000:00:01.4: DPC: containment event, status:0x1f01 source:0x0000
> pcieport 0000:00:01.4: DPC: unmasked uncorrectable error detected
> pcieport 0000:00:01.4: PCIe Bus Error: severity=Uncorrected (Fatal), type=Transaction Layer, (Receiver ID)
> pcieport 0000:00:01.4: device [1022:14ab] error status/mask=00000020/04004000
> pcieport 0000:00:01.4: [ 5] SDES (First)
> nvme nvme2: frozen state error detected, reset controller
> pcieport 0000:00:01.4: DPC: Data Link Layer Link Active not set in 1000 msec
> pcieport 0000:00:01.4: AER: subordinate device reset failed
> pcieport 0000:00:01.4: AER: device recovery failed
> pcieport 0000:00:01.4: pciehp: Slot(16): Link Down
> nvme2n1: detected capacity change from 1953525168 to 0
> pci 0000:04:00.0: Removing from iommu group 49
>
> Dmesg after:
>
> pcieport 0000:00:01.4: pciehp: Slot(16): Link Down
> nvme1n1: detected capacity change from 1953525168 to 0
> pci 0000:04:00.0: Removing from iommu group 37
>
> [1] PCI Express Base Specification Revision 6.0, Dec 16 2021.
> https://members.pcisig.com/wg/PCI-SIG/document/16609
>
> Signed-off-by: Smita Koralahalli <Smita.KoralahalliChannabasappa@xxxxxxx>
> ---
> v2:
> Indentation is taken care. (Bjorn)
> Unrelevant dmesg logs are removed. (Bjorn)
> Rephrased commit message, to be clear on native vs FW-First
> handling. (Bjorn and Sathyanarayanan)
> Prefix changed from pciehp_ to dpc_. (Lukas)
> Clearing ARI and AtomicOp Requester are performed as a part of
> (de-)enumeration in pciehp_unconfigure_device(). (Lukas)
> Changed to clearing all optional capabilities in DEVCTL2.
> OS-First -> native. (Sathyanarayanan)
>
> v3:
> Added error message when root port become inactive.
> Modified commit description to add more details.
> Rearranged code comments and function calls with no functional
> change.
> Additional check for is_hotplug_bridge.
> dpc_completed_waitqueue to wakeup pciehp handler.
> Cleared only Fatal error detected in DEVSTA.
> ---
> drivers/pci/pcie/dpc.c | 58 ++++++++++++++++++++++++++++++++++++++++++
> 1 file changed, 58 insertions(+)
>
> diff --git a/drivers/pci/pcie/dpc.c b/drivers/pci/pcie/dpc.c
> index 3ceed8e3de41..5153ac8ea91c 100644
> --- a/drivers/pci/pcie/dpc.c
> +++ b/drivers/pci/pcie/dpc.c
> @@ -292,10 +292,68 @@ void dpc_process_error(struct pci_dev *pdev)
> }
> }
>
> +static void pci_clear_surpdn_errors(struct pci_dev *pdev)
> +{
> + u16 reg16;
> + u32 reg32;
> +
> + pci_read_config_dword(pdev, pdev->dpc_cap + PCI_EXP_DPC_RP_PIO_STATUS, ®32);
> + pci_write_config_dword(pdev, pdev->dpc_cap + PCI_EXP_DPC_RP_PIO_STATUS, reg32);
It is not clear why you want to clear it.
> +
> + pci_read_config_word(pdev, PCI_STATUS, ®16);
> + pci_write_config_word(pdev, PCI_STATUS, reg16);
Same as above. Can you add some comment about why you are clearing it?
> +
> + pcie_capability_write_word(pdev, PCI_EXP_DEVSTA, PCI_EXP_DEVSTA_FED);
> +}
> +
> +static void dpc_handle_surprise_removal(struct pci_dev *pdev)
> +{
> + if (pdev->dpc_rp_extensions && dpc_wait_rp_inactive(pdev)) {
> + pci_err(pdev, "failed to retrieve DPC root port on async remove\n");
> + goto out;
> + }
> +
> + pci_aer_raw_clear_status(pdev);
> + pci_clear_surpdn_errors(pdev);
> +
> + pci_write_config_word(pdev, pdev->dpc_cap + PCI_EXP_DPC_STATUS,
> + PCI_EXP_DPC_STATUS_TRIGGER);
Don't you need to wait for the link to go down?
> +
> +out:
> + clear_bit(PCI_DPC_RECOVERED, &pdev->priv_flags);
> + wake_up_all(&dpc_completed_waitqueue);
> +}
> +
> +static bool dpc_is_surprise_removal(struct pci_dev *pdev)
> +{
> + u16 status;
> +
> + pci_read_config_word(pdev, pdev->aer_cap + PCI_ERR_UNCOR_STATUS, &status);
> +
> + if (!pdev->is_hotplug_bridge)
> + return false;
> +
> + if (!(status & PCI_ERR_UNC_SURPDN))
> + return false;
> +
> + return true;
> +}
> +
> static irqreturn_t dpc_handler(int irq, void *context)
> {
> struct pci_dev *pdev = context;
>
> + /*
> + * According to Section 6.7.6 of the PCIe Base Spec 6.0, since async
> + * removal might be unexpected, errors might be reported as a side
> + * effect of the event and software should handle them as an expected
> + * part of this event.
> + */
> + if (dpc_is_surprise_removal(pdev)) {
> + dpc_handle_surprise_removal(pdev);
> + return IRQ_HANDLED;
> + }
> +
> dpc_process_error(pdev);
>
> /* We configure DPC so it only triggers on ERR_FATAL */
--
Sathyanarayanan Kuppuswamy
Linux Kernel Developer