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Date:   Mon, 7 May 2018 16:33:44 -0500
From:   Bjorn Helgaas <helgaas@kernel.org>
To:     okaya@codeaurora.org
Cc:     Paul Menzel <pmenzel+linux-pci@molgen.mpg.de>,
        Bjorn Helgaas <bhelgaas@google.com>, linux-pci@vger.kernel.org,
        linux-kernel@vger.kernel.org, Lukas Wunner <lukas@wunner.de>
Subject: Re: pciehp 0000:00:1c.0:pcie004: Timeout on hotplug command 0x1038
 (issued 65284 msec ago)
Message-ID: <20180507213344.GA133147@bhelgaas-glaptop.roam.corp.google.com>
References: <8770820b-85a0-172b-7230-3a44524e6c9f@molgen.mpg.de>
 <20180427192207.GG8199@bhelgaas-glaptop.roam.corp.google.com>
 <43b8ab4a-f8ee-dc96-40ec-e6fdfedd8309@molgen.mpg.de>
 <20180504024527.GE15790@bhelgaas-glaptop.roam.corp.google.com>
 <aa72d3ba089c76449600c22b58a2cafe@codeaurora.org>
 <20180504133327.GF15790@bhelgaas-glaptop.roam.corp.google.com>
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On Fri, May 04, 2018 at 08:33:27AM -0500, Bjorn Helgaas wrote:
> commit b0d6f2230e12c85ae3b65a854a53c67c7c1f6406
> Author: Bjorn Helgaas <bhelgaas@google.com>
> Date:   Thu May 3 18:39:38 2018 -0500
> 
>     PCI: pciehp: Add quirk for Intel Command Completed erratum
>     
>     The Intel CF118 erratum means the controller does not set the Command
>     Completed bit unless writes to the Slot Command register change "Control"
>     bits.  Command Completed is never set for writes that only change software
>     notification "Enable" bits.  This results in timeouts like this:
>     
>       pciehp 0000:00:1c.0:pcie004: Timeout on hotplug command 0x1038 (issued 65284 msec ago)
>     
>     When this erratum is present, avoid these timeouts by marking commands
>     "completed" immediately unless they change the "Control" bits.
>     
>     Here's the text of the erratum from the Intel document:
>     
>       CF118        PCIe Slot Status Register Command Completed bit not always
>                    updated on any configuration write to the Slot Control
>                    Register
>     
>       Problem:     For PCIe root ports (devices 0 - 10) supporting hot-plug,
>                    the Slot Status Register (offset AAh) Command Completed
>                    (bit[4]) status is updated under the following condition:
>                    IOH will set Command Completed bit after delivering the new
>                    commands written in the Slot Controller register (offset
>                    A8h) to VPP. The IOH detects new commands written in Slot
>                    Control register by checking the change of value for Power
>                    Controller Control (bit[10]), Power Indicator Control
>                    (bits[9:8]), Attention Indicator Control (bits[7:6]), or
>                    Electromechanical Interlock Control (bit[11]) fields. Any
>                    other configuration writes to the Slot Control register
>                    without changing the values of these fields will not cause
>                    Command Completed bit to be set.
>     
>                    The PCIe Base Specification Revision 2.0 or later describes
>                    the “Slot Control Register” in section 7.8.10, as follows
>                    (Reference section 7.8.10, Slot Control Register, Offset
>                    18h). In hot-plug capable Downstream Ports, a write to the
>                    Slot Control register must cause a hot-plug command to be
>                    generated (see Section 6.7.3.2 for details on hot-plug
>                    commands). A write to the Slot Control register in a
>                    Downstream Port that is not hotplug capable must not cause a
>                    hot-plug command to be executed.
>     
>                    The PCIe Spec intended that every write to the Slot Control
>                    Register is a command and expected a command complete status
>                    to abstract the VPP implementation specific nuances from the
>                    OS software. IOH PCIe Slot Control Register implementation
>                    is not fully conforming to the PCIe Specification in this
>                    respect.
>     
>       Implication: Software checking on the Command Completed status after
>                    writing to the Slot Control register may time out.
>     
>       Workaround:  Software can read the Slot Control register and compare the
>                    existing and new values to determine if it should check the
>                    Command Completed status after writing to the Slot Control
>                    register.
>     
>     Link: http://www.intel.com/content/www/us/en/processors/xeon/xeon-e7-v2-spec-update.html
>     Link: https://lkml.kernel.org/r/8770820b-85a0-172b-7230-3a44524e6c9f@molgen.mpg.de
>     Reported-by: Paul Menzel <pmenzel+linux-pci@molgen.mpg.de>
>     Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>

I applied this with Paul's tested-by on pci/hotplug for v4.18.

> diff --git a/drivers/pci/hotplug/pciehp_hpc.c b/drivers/pci/hotplug/pciehp_hpc.c
> index 18a42f8f5dc5..e70eba5ea906 100644
> --- a/drivers/pci/hotplug/pciehp_hpc.c
> +++ b/drivers/pci/hotplug/pciehp_hpc.c
> @@ -10,7 +10,6 @@
>   * All rights reserved.
>   *
>   * Send feedback to <greg@kroah.com>,<kristen.c.accardi@intel.com>
> - *
>   */
>  
>  #include <linux/kernel.h>
> @@ -147,25 +146,22 @@ static void pcie_wait_cmd(struct controller *ctrl)
>  	else
>  		rc = pcie_poll_cmd(ctrl, jiffies_to_msecs(timeout));
>  
> -	/*
> -	 * Controllers with errata like Intel CF118 don't generate
> -	 * completion notifications unless the power/indicator/interlock
> -	 * control bits are changed.  On such controllers, we'll emit this
> -	 * timeout message when we wait for completion of commands that
> -	 * don't change those bits, e.g., commands that merely enable
> -	 * interrupts.
> -	 */
>  	if (!rc)
>  		ctrl_info(ctrl, "Timeout on hotplug command %#06x (issued %u msec ago)\n",
>  			  ctrl->slot_ctrl,
>  			  jiffies_to_msecs(jiffies - ctrl->cmd_started));
>  }
>  
> +#define CC_ERRATUM_MASK		(PCI_EXP_SLTCTL_PCC |	\
> +				 PCI_EXP_SLTCTL_PIC |	\
> +				 PCI_EXP_SLTCTL_AIC |	\
> +				 PCI_EXP_SLTCTL_EIC)
> +
>  static void pcie_do_write_cmd(struct controller *ctrl, u16 cmd,
>  			      u16 mask, bool wait)
>  {
>  	struct pci_dev *pdev = ctrl_dev(ctrl);
> -	u16 slot_ctrl;
> +	u16 slot_ctrl_orig, slot_ctrl;
>  
>  	mutex_lock(&ctrl->ctrl_lock);
>  
> @@ -180,6 +176,7 @@ static void pcie_do_write_cmd(struct controller *ctrl, u16 cmd,
>  		goto out;
>  	}
>  
> +	slot_ctrl_orig = slot_ctrl;
>  	slot_ctrl &= ~mask;
>  	slot_ctrl |= (cmd & mask);
>  	ctrl->cmd_busy = 1;
> @@ -188,6 +185,17 @@ static void pcie_do_write_cmd(struct controller *ctrl, u16 cmd,
>  	ctrl->cmd_started = jiffies;
>  	ctrl->slot_ctrl = slot_ctrl;
>  
> +	/*
> +	 * Controllers with the Intel CF118 and similar errata advertise
> +	 * Command Completed support, but they only set Command Completed
> +	 * if we change the "Control" bits for power, power indicator,
> +	 * attention indicator, or interlock.  If we only change the
> +	 * "Enable" bits, they never set the Command Completed bit.
> +	 */
> +	if (pdev->broken_cmd_compl &&
> +	    (slot_ctrl_orig & CC_ERRATUM_MASK) == (slot_ctrl & CC_ERRATUM_MASK))
> +		ctrl->cmd_busy = 0;
> +
>  	/*
>  	 * Optionally wait for the hardware to be ready for a new command,
>  	 * indicating completion of the above issued command.
> @@ -861,7 +869,7 @@ struct controller *pcie_init(struct pcie_device *dev)
>  		PCI_EXP_SLTSTA_MRLSC | PCI_EXP_SLTSTA_CC |
>  		PCI_EXP_SLTSTA_DLLSC);
>  
> -	ctrl_info(ctrl, "Slot #%d AttnBtn%c PwrCtrl%c MRL%c AttnInd%c PwrInd%c HotPlug%c Surprise%c Interlock%c NoCompl%c LLActRep%c\n",
> +	ctrl_info(ctrl, "Slot #%d AttnBtn%c PwrCtrl%c MRL%c AttnInd%c PwrInd%c HotPlug%c Surprise%c Interlock%c NoCompl%c LLActRep%c%s\n",
>  		(slot_cap & PCI_EXP_SLTCAP_PSN) >> 19,
>  		FLAG(slot_cap, PCI_EXP_SLTCAP_ABP),
>  		FLAG(slot_cap, PCI_EXP_SLTCAP_PCP),
> @@ -872,7 +880,8 @@ struct controller *pcie_init(struct pcie_device *dev)
>  		FLAG(slot_cap, PCI_EXP_SLTCAP_HPS),
>  		FLAG(slot_cap, PCI_EXP_SLTCAP_EIP),
>  		FLAG(slot_cap, PCI_EXP_SLTCAP_NCCS),
> -		FLAG(link_cap, PCI_EXP_LNKCAP_DLLLARC));
> +		FLAG(link_cap, PCI_EXP_LNKCAP_DLLLARC),
> +		pdev->broken_cmd_compl ? " (with Cmd Compl erratum)" : "");
>  
>  	if (pcie_init_slot(ctrl))
>  		goto abort_ctrl;
> @@ -891,3 +900,17 @@ void pciehp_release_ctrl(struct controller *ctrl)
>  	pcie_cleanup_slot(ctrl);
>  	kfree(ctrl);
>  }
> +
> +static void quirk_cmd_compl(struct pci_dev *pdev)
> +{
> +	u32 slot_cap;
> +
> +	if (pci_is_pcie(pdev)) {
> +		pcie_capability_read_dword(pdev, PCI_EXP_SLTCAP, &slot_cap);
> +		if (slot_cap & PCI_EXP_SLTCAP_HPC &&
> +		    !(slot_cap & PCI_EXP_SLTCAP_NCCS))
> +			pdev->broken_cmd_compl = 1;
> +	}
> +}
> +DECLARE_PCI_FIXUP_CLASS_EARLY(PCI_VENDOR_ID_INTEL, PCI_ANY_ID,
> +			      PCI_CLASS_BRIDGE_PCI, 8, quirk_cmd_compl);
> diff --git a/include/linux/pci.h b/include/linux/pci.h
> index 73178a2fcee0..60cb5350ad28 100644
> --- a/include/linux/pci.h
> +++ b/include/linux/pci.h
> @@ -406,6 +406,9 @@ struct pci_dev {
>  	struct bin_attribute *res_attr[DEVICE_COUNT_RESOURCE]; /* sysfs file for resources */
>  	struct bin_attribute *res_attr_wc[DEVICE_COUNT_RESOURCE]; /* sysfs file for WC mapping of resources */
>  
> +#ifdef CONFIG_HOTPLUG_PCI_PCIE
> +	unsigned int	broken_cmd_compl:1;	/* Command Complete broken */
> +#endif
>  #ifdef CONFIG_PCIE_PTM
>  	unsigned int	ptm_root:1;
>  	unsigned int	ptm_enabled:1;