Date:   Tue, 25 Feb 2020 19:02:31 -0600
From:   Bjorn Helgaas <helgaas@...nel.org>
To:     sathyanarayanan.kuppuswamy@...ux.intel.com
Cc:     linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org,
        ashok.raj@...el.com
Subject: Re: [PATCH v15 4/5] PCI/DPC: Add Error Disconnect Recover (EDR)
 support

On Thu, Feb 13, 2020 at 10:20:16AM -0800, sathyanarayanan.kuppuswamy@...ux.intel.com wrote:
> From: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@...ux.intel.com>
> 
> As per ACPI specification r6.3, sec 5.6.6, when firmware owns Downstream
> Port Containment (DPC), its expected to use the "Error Disconnect
> Recover" (EDR) notification to alert OSPM of a DPC event and if OS
> supports EDR, its expected to handle the software state invalidation and
> port recovery in OS, and also let firmware know the recovery status via
> _OST ACPI call. Related _OST status codes can be found in ACPI
> specification r6.3, sec 6.3.5.2.
> 
> Also, as per PCI firmware specification r3.2 Downstream Port Containment
> Related Enhancements ECN, sec 4.5.1, table 4-6, If DPC is controlled by
> firmware (firmware first mode), firmware is responsible for
> configuring the DPC and OS is responsible for error recovery. Also, OS
> is allowed to modify DPC registers only during the EDR notification
> window.
> 
> Signed-off-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@...ux.intel.com>
> ---
>  drivers/pci/pci-acpi.c    |   3 +
>  drivers/pci/pcie/Kconfig  |  10 ++
>  drivers/pci/pcie/Makefile |   1 +
>  drivers/pci/pcie/edr.c    | 257 ++++++++++++++++++++++++++++++++++++++
>  include/linux/pci-acpi.h  |   8 ++
>  5 files changed, 279 insertions(+)
>  create mode 100644 drivers/pci/pcie/edr.c
> 
> diff --git a/drivers/pci/pci-acpi.c b/drivers/pci/pci-acpi.c
> index 0c02d500158f..6af5d6a04990 100644
> --- a/drivers/pci/pci-acpi.c
> +++ b/drivers/pci/pci-acpi.c
> @@ -1258,6 +1258,7 @@ static void pci_acpi_setup(struct device *dev)
>  
>  	acpi_pci_wakeup(pci_dev, false);
>  	acpi_device_power_add_dependent(adev, dev);
> +	pci_acpi_add_edr_notifier(pci_dev);
>  }
>  
>  static void pci_acpi_cleanup(struct device *dev)
> @@ -1276,6 +1277,8 @@ static void pci_acpi_cleanup(struct device *dev)
>  
>  		device_set_wakeup_capable(dev, false);
>  	}
> +
> +	pci_acpi_remove_edr_notifier(pci_dev);
>  }
>  
>  static bool pci_acpi_bus_match(struct device *dev)
> diff --git a/drivers/pci/pcie/Kconfig b/drivers/pci/pcie/Kconfig
> index 6e3c04b46fb1..772b1f4cb19e 100644
> --- a/drivers/pci/pcie/Kconfig
> +++ b/drivers/pci/pcie/Kconfig
> @@ -140,3 +140,13 @@ config PCIE_BW
>  	  This enables PCI Express Bandwidth Change Notification.  If
>  	  you know link width or rate changes occur only to correct
>  	  unreliable links, you may answer Y.
> +
> +config PCIE_EDR
> +	bool "PCI Express Error Disconnect Recover support"
> +	depends on PCIE_DPC && ACPI
> +	help
> +	  This option adds Error Disconnect Recover support as specified
> +	  in the Downstream Port Containment Related Enhancements ECN to
> +	  the PCI Firmware Specification r3.2.  Enable this if you want to
> +	  support hybrid DPC model which uses both firmware and OS to
> +	  implement DPC.
> diff --git a/drivers/pci/pcie/Makefile b/drivers/pci/pcie/Makefile
> index efb9d2e71e9e..68da9280ff11 100644
> --- a/drivers/pci/pcie/Makefile
> +++ b/drivers/pci/pcie/Makefile
> @@ -13,3 +13,4 @@ obj-$(CONFIG_PCIE_PME)		+= pme.o
>  obj-$(CONFIG_PCIE_DPC)		+= dpc.o
>  obj-$(CONFIG_PCIE_PTM)		+= ptm.o
>  obj-$(CONFIG_PCIE_BW)		+= bw_notification.o
> +obj-$(CONFIG_PCIE_EDR)		+= edr.o
> diff --git a/drivers/pci/pcie/edr.c b/drivers/pci/pcie/edr.c
> new file mode 100644
> index 000000000000..b3e9103585a1
> --- /dev/null
> +++ b/drivers/pci/pcie/edr.c
> @@ -0,0 +1,257 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * PCI DPC Error Disconnect Recover support driver
> + * Author: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@...ux.intel.com>
> + *
> + * Copyright (C) 2020 Intel Corp.
> + */
> +
> +#define dev_fmt(fmt) "EDR: " fmt
> +
> +#include <linux/pci.h>
> +#include <linux/pci-acpi.h>
> +
> +#include "portdrv.h"
> +#include "dpc.h"
> +#include "../pci.h"
> +
> +#define EDR_PORT_ENABLE_DSM		0x0C
> +#define EDR_PORT_LOCATE_DSM		0x0D
> +#define EDR_OST_SUCCESS			0x80
> +#define EDR_OST_FAILED			0x81
> +
> +/*
> + * _DSM wrapper function to enable/disable DPC port.
> + * @pdev   : PCI device structure.
> + * @enable: status of DPC port (0 or 1).

Either line up these colons or join them with the parameter names
(also below).

> + * returns 0 on success or errno on failure.
> + */
> +static int acpi_enable_dpc_port(struct pci_dev *pdev, bool enable)

We only call this with "true", so the "enable" parameter is pointless.

> +{
> +	struct acpi_device *adev = ACPI_COMPANION(&pdev->dev);
> +	union acpi_object *obj, argv4, req;
> +	int status = 0;
> +
> +	req.type = ACPI_TYPE_INTEGER;
> +	req.integer.value = enable;
> +
> +	argv4.type = ACPI_TYPE_PACKAGE;
> +	argv4.package.count = 1;
> +	argv4.package.elements = &req;
> +
> +	/*
> +	 * Per the Downstream Port Containment Related Enhancements ECN to
> +	 * the PCI Firmware Specification r3.2, sec 4.6.12,
> +	 * EDR_PORT_ENABLE_DSM is optional.  Return success if it's not
> +	 * implemented.
> +	 */
> +	obj = acpi_evaluate_dsm(adev->handle, &pci_acpi_dsm_guid, 5,
> +				EDR_PORT_ENABLE_DSM, &argv4);
> +	if (!obj)
> +		return 0;
> +
> +	if (obj->type != ACPI_TYPE_INTEGER || obj->integer.value != enable)
> +		status = -EIO;
> +
> +	ACPI_FREE(obj);
> +
> +	return status;
> +}
> +
> +/*
> + * _DSM wrapper function to locate DPC port.
> + * @pdev   : Device which received EDR event.
> + *
> + * returns pci_dev or NULL.
> + */
> +static struct pci_dev *acpi_locate_dpc_port(struct pci_dev *pdev)
> +{
> +	struct acpi_device *adev = ACPI_COMPANION(&pdev->dev);
> +	union acpi_object *obj;
> +	u16 port;
> +
> +	obj = acpi_evaluate_dsm(adev->handle, &pci_acpi_dsm_guid, 5,
> +				EDR_PORT_LOCATE_DSM, NULL);
> +	if (!obj)
> +		return pci_dev_get(pdev);
> +
> +	if (obj->type != ACPI_TYPE_INTEGER) {

If this happens, it's a firmware defect, isn't it?  I think maybe we
should warn here.  I know we warn below ("No valid port found"), but
that doesn't give any clue about the fact that firmware screwed up.

> +		ACPI_FREE(obj);
> +		return NULL;
> +	}
> +
> +	/*
> +	 * Firmware returns DPC port BDF details in following format:
> +	 *	15:8 = bus
> +	 *	 7:3 = device
> +	 *	 2:0 = function
> +	 */
> +	port = obj->integer.value;
> +
> +	ACPI_FREE(obj);
> +
> +	return pci_get_domain_bus_and_slot(pci_domain_nr(pdev->bus),
> +					   PCI_BUS_NUM(port), port & 0xff);
> +}
> +
> +/*
> + * _OST wrapper function to let firmware know the status of EDR event.
> + * @pdev   : Device used to send _OST.
> + * @edev   : Device which experienced EDR event.
> + * @status: Status of EDR event.
> + */
> +static int acpi_send_edr_status(struct pci_dev *pdev, struct pci_dev *edev,
> +				u16 status)
> +{
> +	struct acpi_device *adev = ACPI_COMPANION(&pdev->dev);
> +	u32 ost_status;
> +
> +	pci_dbg(pdev, "Sending EDR status :%#x\n", status);
> +
> +	ost_status =  PCI_DEVID(edev->bus->number, edev->devfn);
> +	ost_status = (ost_status << 16) | status;
> +
> +	status = acpi_evaluate_ost(adev->handle,
> +				   ACPI_NOTIFY_DISCONNECT_RECOVER,
> +				   ost_status, NULL);
> +	if (ACPI_FAILURE(status))
> +		return -EINVAL;
> +
> +	return 0;
> +}
> +
> +pci_ers_result_t edr_dpc_reset_link(void *cb_data)
> +{
> +	return dpc_reset_link_common(cb_data);
> +}
> +
> +static void edr_handle_event(acpi_handle handle, u32 event, void *data)
> +{
> +	struct dpc_dev *dpc = data, ndpc;

There's actually very little use of struct dpc_dev in this file.  I
bet with a little elbow grease, we could remove it completely and just
use the pci_dev * or maybe an opaque pointer.

> +	struct pci_dev *pdev = dpc->pdev;
> +	pci_ers_result_t estate = PCI_ERS_RESULT_DISCONNECT;
> +	u16 status;
> +
> +	pci_info(pdev, "ACPI event %#x received\n", event);
> +
> +	if (event != ACPI_NOTIFY_DISCONNECT_RECOVER)
> +		return;
> +
> +	/*
> +	 * Check if _DSM(0xD) is available, and if present locate the
> +	 * port which issued EDR event.
> +	 */
> +	pdev = acpi_locate_dpc_port(pdev);

This function name should include "get" since it's part of the
pci_dev_get()/pci_dev_put() sequence.

> +	if (!pdev) {
> +		pci_err(dpc->pdev, "No valid port found\n");
> +		return;
> +	}
> +
> +	if (pdev != dpc->pdev) {
> +		pci_warn(pdev, "Initializing dpc again\n");
> +		dpc_dev_init(pdev, &ndpc);

This seems...  I'm not sure what.  I guess it's really just reading
the DPC capability for use by dpc_process_error(), so maybe it's OK.
But it's a little strange to read.

Is this something we should be warning about?  I think the ECR says
it's legitimate to return a child device, doesn't it?

> +		dpc= &ndpc;

Space before "=".

> +	}
> +
> +	/*
> +	 * If port does not support DPC, just send the OST:
> +	 */
> +	if (!dpc->cap_pos)
> +		goto send_ost;
> +
> +	/* Check if there is a valid DPC trigger */
> +	pci_read_config_word(pdev, dpc->cap_pos + PCI_EXP_DPC_STATUS, &status);
> +	if (!(status & PCI_EXP_DPC_STATUS_TRIGGER)) {
> +		pci_err(pdev, "Invalid DPC trigger %#010x\n", status);
> +		goto send_ost;
> +	}
> +
> +	dpc_process_error(dpc);
> +
> +	/* Clear AER registers */
> +	pci_aer_clear_err_uncor_status(pdev);
> +	pci_aer_clear_err_fatal_status(pdev);
> +	pci_aer_clear_err_status_regs(pdev);
> +
> +	/*
> +	 * Irrespective of whether the DPC event is triggered by
> +	 * ERR_FATAL or ERR_NONFATAL, since the link is already down,
> +	 * use the FATAL error recovery path for both cases.
> +	 */
> +	estate = pcie_do_recovery_common(pdev, pci_channel_io_frozen, -1,
> +					 edr_dpc_reset_link, dpc);
> +send_ost:
> +
> +	/* Use ACPI handle of DPC event device for sending EDR status */
> +	dpc = data;

I think it'd be clearer to reserve "dpc" for the device that received
the notification and to which we send the status, and use a different
"e_dpc" or something for the dpc_process_error() and related code.

> +	/*
> +	 * If recovery is successful, send _OST(0xF, BDF << 16 | 0x80)
> +	 * to firmware. If not successful, send _OST(0xF, BDF << 16 | 0x81).
> +	 */
> +	if (estate == PCI_ERS_RESULT_RECOVERED)
> +		acpi_send_edr_status(dpc->pdev, pdev, EDR_OST_SUCCESS);
> +	else
> +		acpi_send_edr_status(dpc->pdev, pdev, EDR_OST_FAILED);
> +
> +	pci_dev_put(pdev);
> +}
> +
> +int pci_acpi_add_edr_notifier(struct pci_dev *pdev)
> +{
> +	struct acpi_device *adev = ACPI_COMPANION(&pdev->dev);
> +	struct dpc_dev *dpc;
> +	acpi_status astatus;
> +	int status;
> +
> +	/*
> +	 * Per the Downstream Port Containment Related Enhancements ECN to
> +	 * the PCI Firmware Spec, r3.2, sec 4.5.1, table 4-6, EDR support
> +	 * can only be enabled if DPC is controlled by firmware.
> +	 *
> +	 * TODO: Remove dependency on ACPI FIRMWARE_FIRST bit to
> +	 * determine ownership of DPC between firmware or OS.

Extend the comment to say how we *should* determine ownership.

> +	 */
> +	if (!pcie_aer_get_firmware_first(pdev) || pcie_ports_dpc_native)
> +		return -ENODEV;
> +
> +	if (!adev)
> +		return 0;
> +
> +	dpc = devm_kzalloc(&pdev->dev, sizeof(*dpc), GFP_KERNEL);

This kzalloc should be in dpc.c, not here.

And I don't see a corresponding free.

> +	if (!dpc)
> +		return -ENOMEM;
> +
> +	dpc_dev_init(pdev, dpc);
> +
> +	astatus = acpi_install_notify_handler(adev->handle,
> +					      ACPI_SYSTEM_NOTIFY,
> +					      edr_handle_event, dpc);
> +	if (ACPI_FAILURE(astatus)) {
> +		pci_err(pdev, "Install ACPI_SYSTEM_NOTIFY handler failed\n");
> +		return -EBUSY;
> +	}
> +
> +	status = acpi_enable_dpc_port(pdev, true);
> +	if (status) {
> +		pci_warn(pdev, "Enable DPC port failed\n");
> +		acpi_remove_notify_handler(adev->handle,
> +					   ACPI_SYSTEM_NOTIFY,
> +					   edr_handle_event);
> +		return status;
> +	}
> +
> +	return 0;
> +}
> +
> +void pci_acpi_remove_edr_notifier(struct pci_dev *pdev)
> +{
> +	struct acpi_device *adev = ACPI_COMPANION(&pdev->dev);
> +
> +	if (!adev)
> +		return;
> +
> +	acpi_remove_notify_handler(adev->handle, ACPI_SYSTEM_NOTIFY,
> +				   edr_handle_event);
> +}
> diff --git a/include/linux/pci-acpi.h b/include/linux/pci-acpi.h
> index 62b7fdcc661c..a430e5fc50f3 100644
> --- a/include/linux/pci-acpi.h
> +++ b/include/linux/pci-acpi.h
> @@ -112,6 +112,14 @@ extern const guid_t pci_acpi_dsm_guid;
>  #define RESET_DELAY_DSM			0x08
>  #define FUNCTION_DELAY_DSM		0x09
>  
> +#ifdef CONFIG_PCIE_EDR
> +int pci_acpi_add_edr_notifier(struct pci_dev *pdev);
> +void pci_acpi_remove_edr_notifier(struct pci_dev *pdev);
> +#else
> +static inline int pci_acpi_add_edr_notifier(struct pci_dev *pdev) { return 0; }
> +static inline void pci_acpi_remove_edr_notifier(struct pci_dev *pdev) { }
> +#endif /* CONFIG_PCIE_EDR */
> +
>  #else	/* CONFIG_ACPI */
>  static inline void acpi_pci_add_bus(struct pci_bus *bus) { }
>  static inline void acpi_pci_remove_bus(struct pci_bus *bus) { }
> -- 
> 2.21.0
> 

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