Re: [Update][PATCH] PCIe / hotplug: Drop pointless ACPI-based "slot detection" check

From: Bjorn Helgaas <bhelgaas@google.com>
To: "Rafael J. Wysocki" <rjw@rjwysocki.net>
Cc: Jarod Wilson <jarod@redhat.com>,
	linux-kernel@vger.kernel.org, Len Brown <lenb@kernel.org>,
	linux-acpi@vger.kernel.org, linux-pci@vger.kernel.org
Subject: Re: [Update][PATCH] PCIe / hotplug: Drop pointless ACPI-based "slot detection" check
Date: Thu, 21 May 2015 11:11:46 -0500	[thread overview]
Message-ID: <20150521161146.GE32152@google.com> (raw)
In-Reply-To: <1573807.HQlNd2BFYP@vostro.rjw.lan>

On Tue, May 19, 2015 at 03:27:58PM +0200, Rafael J. Wysocki wrote:
> From: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
> 
> Jarod Wilson reports that the expresscard hotplug setup doesn't work
> on HP ZBook G2.  The problem turns out to be the ACPI-based "slot
> detection" code called from pciehp_probe() which tries to use some
> questionable heuristics based on what ACPI objects are present for
> the PCIe port device at hand to figure out whether or not to register
> a hotplug slot for that port.
> 
> That code is used if there is at least one PCIe port having an ACPI
> device configuration object related to hotplug (such as _EJ0 or _RMV)
> and the Thunderbolt port on the affected machine has _RMV.  Of course,
> Thunderbolt and PCIe native hotplug need not be mutually exclusive
> (as they aren't on the machine in question), so that rule is simply
> incorrect.
> 
> Moreover, the ACPI-based "slot detection" check does not add any
> value if pciehp_probe() is called at all and the service type of the
> device object it has been called for is PCIE_PORT_SERVICE_HP, because
> PCIe hotplug services are only registered if the _OSC handshake in
> acpi_pci_root_add() allows the kernel to control the PCIe native
> hotplug feature.  No more checks need to be carried out to decide
> whether or not to register a native PCIe hotlug slot in that case.
> 
> For the above reasons, make pciehp_probe() check if it has been
> called for the right service type and drop the pointless ACPI-based
> "slot detection" check from it.  Also remove the entire code whose
> only user is that check (the entire pciehp_acpi.c file goes away
> as a result) and drop function headers related to it from the
> internal PCIeHP header file.
> 
> Link: http://marc.info/?t=143163219300002&r=1&w=2
> Link: https://bugzilla.kernel.org/show_bug.cgi?id=98581
> Reported-by: Jarod Wilson <jarod@redhat.com>
> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

This is awesome!  Applied to pci/hotplug for v4.2, with Jarod's
reviewed/tested-by.

I suspect a lot of this stuff dates back to when acpiphp and pciehp could
be modules, and one driver really couldn't know whether the other was up
to.  In any event, I think it will be much more predictable and
maintainable now.

Bjorn

> ---
> 
> Changes in Makefile were missing from the previous version.
> 
> Bjorn, that's -stable material I think.  It should be applicable at least
> since commit 5ba113f7c4fb (PCI: acpiphp: Handle PCIe ports without native
> hotplug capability) that was shipped in 3.10.
> 
> Thanks!
> 
> ---
>  drivers/pci/hotplug/Makefile      |    3 
>  drivers/pci/hotplug/pciehp.h      |   17 ----
>  drivers/pci/hotplug/pciehp_acpi.c |  137 --------------------------------------
>  drivers/pci/hotplug/pciehp_core.c |   10 --
>  4 files changed, 3 insertions(+), 164 deletions(-)
> 
> Index: linux-pm/drivers/pci/hotplug/pciehp_core.c
> ===================================================================
> --- linux-pm.orig/drivers/pci/hotplug/pciehp_core.c
> +++ linux-pm/drivers/pci/hotplug/pciehp_core.c
> @@ -248,12 +248,9 @@ static int pciehp_probe(struct pcie_devi
>  	struct slot *slot;
>  	u8 occupied, poweron;
>  
> -	if (pciehp_force)
> -		dev_info(&dev->device,
> -			 "Bypassing BIOS check for pciehp use on %s\n",
> -			 pci_name(dev->port));
> -	else if (pciehp_acpi_slot_detection_check(dev->port))
> -		goto err_out_none;
> +	/* If this is not a "hotplug" service, we have no business here. */
> +	if (dev->service != PCIE_PORT_SERVICE_HP)
> +		return -ENODEV;
>  
>  	if (!dev->port->subordinate) {
>  		/* Can happen if we run out of bus numbers during probe */
> @@ -366,7 +363,6 @@ static int __init pcied_init(void)
>  {
>  	int retval = 0;
>  
> -	pciehp_firmware_init();
>  	retval = pcie_port_service_register(&hpdriver_portdrv);
>  	dbg("pcie_port_service_register = %d\n", retval);
>  	info(DRIVER_DESC " version: " DRIVER_VERSION "\n");
> Index: linux-pm/drivers/pci/hotplug/pciehp_acpi.c
> ===================================================================
> --- linux-pm.orig/drivers/pci/hotplug/pciehp_acpi.c
> +++ /dev/null
> @@ -1,137 +0,0 @@
> -/*
> - * ACPI related functions for PCI Express Hot Plug driver.
> - *
> - * Copyright (C) 2008 Kenji Kaneshige
> - * Copyright (C) 2008 Fujitsu Limited.
> - *
> - * All rights reserved.
> - *
> - * This program is free software; you can redistribute it and/or modify
> - * it under the terms of the GNU General Public License as published by
> - * the Free Software Foundation; either version 2 of the License, or (at
> - * your option) any later version.
> - *
> - * This program is distributed in the hope that it will be useful, but
> - * WITHOUT ANY WARRANTY; without even the implied warranty of
> - * MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE, GOOD TITLE or
> - * NON INFRINGEMENT.  See the GNU General Public License for more
> - * details.
> - *
> - * You should have received a copy of the GNU General Public License
> - * along with this program; if not, write to the Free Software
> - * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
> - *
> - */
> -
> -#include <linux/acpi.h>
> -#include <linux/pci.h>
> -#include <linux/pci_hotplug.h>
> -#include <linux/slab.h>
> -#include <linux/module.h>
> -#include "pciehp.h"
> -
> -#define PCIEHP_DETECT_PCIE	(0)
> -#define PCIEHP_DETECT_ACPI	(1)
> -#define PCIEHP_DETECT_AUTO	(2)
> -#define PCIEHP_DETECT_DEFAULT	PCIEHP_DETECT_AUTO
> -
> -struct dummy_slot {
> -	u32 number;
> -	struct list_head list;
> -};
> -
> -static int slot_detection_mode;
> -static char *pciehp_detect_mode;
> -module_param(pciehp_detect_mode, charp, 0444);
> -MODULE_PARM_DESC(pciehp_detect_mode,
> -	 "Slot detection mode: pcie, acpi, auto\n"
> -	 "  pcie          - Use PCIe based slot detection\n"
> -	 "  acpi          - Use ACPI for slot detection\n"
> -	 "  auto(default) - Auto select mode. Use acpi option if duplicate\n"
> -	 "                  slot ids are found. Otherwise, use pcie option\n");
> -
> -int pciehp_acpi_slot_detection_check(struct pci_dev *dev)
> -{
> -	if (slot_detection_mode != PCIEHP_DETECT_ACPI)
> -		return 0;
> -	if (acpi_pci_detect_ejectable(ACPI_HANDLE(&dev->dev)))
> -		return 0;
> -	return -ENODEV;
> -}
> -
> -static int __init parse_detect_mode(void)
> -{
> -	if (!pciehp_detect_mode)
> -		return PCIEHP_DETECT_DEFAULT;
> -	if (!strcmp(pciehp_detect_mode, "pcie"))
> -		return PCIEHP_DETECT_PCIE;
> -	if (!strcmp(pciehp_detect_mode, "acpi"))
> -		return PCIEHP_DETECT_ACPI;
> -	if (!strcmp(pciehp_detect_mode, "auto"))
> -		return PCIEHP_DETECT_AUTO;
> -	warn("bad specifier '%s' for pciehp_detect_mode. Use default\n",
> -	     pciehp_detect_mode);
> -	return PCIEHP_DETECT_DEFAULT;
> -}
> -
> -static int __initdata dup_slot_id;
> -static int __initdata acpi_slot_detected;
> -static struct list_head __initdata dummy_slots = LIST_HEAD_INIT(dummy_slots);
> -
> -/* Dummy driver for duplicate name detection */
> -static int __init dummy_probe(struct pcie_device *dev)
> -{
> -	u32 slot_cap;
> -	acpi_handle handle;
> -	struct dummy_slot *slot, *tmp;
> -	struct pci_dev *pdev = dev->port;
> -
> -	pcie_capability_read_dword(pdev, PCI_EXP_SLTCAP, &slot_cap);
> -	slot = kzalloc(sizeof(*slot), GFP_KERNEL);
> -	if (!slot)
> -		return -ENOMEM;
> -	slot->number = (slot_cap & PCI_EXP_SLTCAP_PSN) >> 19;
> -	list_for_each_entry(tmp, &dummy_slots, list) {
> -		if (tmp->number == slot->number)
> -			dup_slot_id++;
> -	}
> -	list_add_tail(&slot->list, &dummy_slots);
> -	handle = ACPI_HANDLE(&pdev->dev);
> -	if (!acpi_slot_detected && acpi_pci_detect_ejectable(handle))
> -		acpi_slot_detected = 1;
> -	return -ENODEV;         /* dummy driver always returns error */
> -}
> -
> -static struct pcie_port_service_driver __initdata dummy_driver = {
> -	.name		= "pciehp_dummy",
> -	.port_type	= PCIE_ANY_PORT,
> -	.service	= PCIE_PORT_SERVICE_HP,
> -	.probe		= dummy_probe,
> -};
> -
> -static int __init select_detection_mode(void)
> -{
> -	struct dummy_slot *slot, *tmp;
> -
> -	if (pcie_port_service_register(&dummy_driver))
> -		return PCIEHP_DETECT_ACPI;
> -	pcie_port_service_unregister(&dummy_driver);
> -	list_for_each_entry_safe(slot, tmp, &dummy_slots, list) {
> -		list_del(&slot->list);
> -		kfree(slot);
> -	}
> -	if (acpi_slot_detected && dup_slot_id)
> -		return PCIEHP_DETECT_ACPI;
> -	return PCIEHP_DETECT_PCIE;
> -}
> -
> -void __init pciehp_acpi_slot_detection_init(void)
> -{
> -	slot_detection_mode = parse_detect_mode();
> -	if (slot_detection_mode != PCIEHP_DETECT_AUTO)
> -		goto out;
> -	slot_detection_mode = select_detection_mode();
> -out:
> -	if (slot_detection_mode == PCIEHP_DETECT_ACPI)
> -		info("Using ACPI for slot detection.\n");
> -}
> Index: linux-pm/drivers/pci/hotplug/pciehp.h
> ===================================================================
> --- linux-pm.orig/drivers/pci/hotplug/pciehp.h
> +++ linux-pm/drivers/pci/hotplug/pciehp.h
> @@ -167,21 +167,4 @@ static inline const char *slot_name(stru
>  	return hotplug_slot_name(slot->hotplug_slot);
>  }
>  
> -#ifdef CONFIG_ACPI
> -#include <linux/pci-acpi.h>
> -
> -void __init pciehp_acpi_slot_detection_init(void);
> -int pciehp_acpi_slot_detection_check(struct pci_dev *dev);
> -
> -static inline void pciehp_firmware_init(void)
> -{
> -	pciehp_acpi_slot_detection_init();
> -}
> -#else
> -#define pciehp_firmware_init()				do {} while (0)
> -static inline int pciehp_acpi_slot_detection_check(struct pci_dev *dev)
> -{
> -	return 0;
> -}
> -#endif				/* CONFIG_ACPI */
>  #endif				/* _PCIEHP_H */
> Index: linux-pm/drivers/pci/hotplug/Makefile
> ===================================================================
> --- linux-pm.orig/drivers/pci/hotplug/Makefile
> +++ linux-pm/drivers/pci/hotplug/Makefile
> @@ -61,9 +61,6 @@ pciehp-objs		:=	pciehp_core.o	\
>  				pciehp_ctrl.o	\
>  				pciehp_pci.o	\
>  				pciehp_hpc.o
> -ifdef CONFIG_ACPI
> -pciehp-objs		+=	pciehp_acpi.o
> -endif
>  
>  shpchp-objs		:=	shpchp_core.o	\
>  				shpchp_ctrl.o	\
> 