Date:	Wed, 21 Oct 2015 15:23:23 -0500
From:	Bjorn Helgaas <helgaas@...nel.org>
To:	Guenter Roeck <linux@...ck-us.net>
Cc:	linux-pci@...r.kernel.org, Bjorn Helgaas <bhelgaas@...gle.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH 2/2] PCI: pciehp: Add support for delayed power-on

Hi Guenter,

On Mon, Oct 12, 2015 at 12:10:13PM -0700, Guenter Roeck wrote:
> Some oddball devices may experience a PCIe link flap after power-on.
> This may result in the following sequence of events.
> 
> fpc0 kernel: pciehp 0000:02:08.0:pcie24: Card present on Slot(0)
> fpc0 kernel: pciehp 0000:02:08.0:pcie24: slot(0): Link Up event
> fpc0 kernel: pciehp 0000:02:08.0:pcie24: Link Up event ignored on slot(0): already powering on
> fpc0 kernel: pciehp 0000:02:08.0:pcie24: slot(0): Link Down event
> fpc0 kernel: pciehp 0000:02:08.0:pcie24: Link Down event queued on slot(0): currently getting powered on
> fpc0 kernel: pciehp 0000:02:08.0:pcie24: slot(0): Link Up event
> fpc0 kernel: pciehp 0000:02:08.0:pcie24: Link Up event queued on slot(0): currently getting powered off

I'm really interested in how this happens.  I'm not happy with the
pciehp state machine, and I wonder if it is causing or obscuring this
problem.

For example, pcie_isr() reads PCI_EXP_SLTSTA to find out what
happened.  Then it queues events (attention button, presence detect
changed, etc.)  Along the way, we re-read PCI_EXP_SLTSTA.  That seems
wrong to me -- I think we should capture the state *once*, save it,
and act on it.  If we re-read it, we'll see transitions that might
confuse us.

Similarly, pcie_isr() reads and acts on PCI_EXP_LNKSTA (via
pciehp_check_link_active()).  I think we should capture and save that
at the same time we capture PCI_EXP_SLTSTA, before we queue up work
events that are going to change things.

And I'm not sure it's really necessary for pcie_isr() to queue up
*separate* events for attention button, presence detect, power fault,
and link state events.  I suspect that could throw in extraneous
events that confuse things.  For instance, I think it's possible for
pcie_isr() to see a single interrupt with PCI_EXP_SLTSTA showing both
a presence detect change (card now present) and a link state change
(link now up).  It will queue two events and we'll probably see a
"Link Up event ignored" message.  I think it would be better if
pcie_isr() captured the register values we need, bundled them up,
and queued a single work item to deal with them.

> This causes the driver for affected devices to be instantiated, removed,
> and re-instantiated. This can result in problems, for example if the device
> in question provides gpio pins or interrupts which are used by other
> drivers. For example, the removal can result in errors such as
> the following.
> 
> fpc0 kernel: remove_proc_entry: removing non-empty directory 'irq/148',
> 	leaking at least 'pic0'
> fpc0 kernel: ------------[ cut here ]------------
> fpc0 kernel: WARNING: at /home/p2020/linux-freescale/fs/proc/generic.c:575

Something's definitely wrong here, but shouldn't we be able to add and
remove a device as many times as we want, as quickly as we want,
without problems?  Maybe this particular issue is a driver problem or
a core problem with the proc file maintenance?  I wonder if this is
something we could reproduce without pciehp at all, just by inserting
and removing a module?

> Add support for per-port power-on delay to avoid this situation. This can
> be enabled globally with the pciehp_poweron_delay module parameter, or
> per port (using a quirks function) with a new poweron_delay flag in
> struct pci_dev.
> 
> With this patch, the link flap still occurs, but because of the delayed
> insertion the driver is not immediately instantiated, and the above error
> is no longer seen.

We might have to do something like this eventually, but I'd really
like to see if we can simplify the pciehp state machine a little
before we add more stuff to it.

> Signed-off-by: Guenter Roeck <linux@...ck-us.net>
> ---
> We started seeing this problem after the recent rework of link status
> change handling. I think the up/down/up sequence was previously just
> ignored or folded into a single event (and sometimes resulted in a stuck
> state machine).
> I would like to see this patch upstream, but I am not sure if the problem
> is seen anywhere but on the hardware I am dealing with, and I can
> understand if others don't want to pollute the pcie hotplug code with
> such workarounds. Also, maybe someone has a better idea on how to handle
> the situation, so I marked the patch as RFC.
> 
>  drivers/pci/hotplug/pciehp.h      |  5 ++++-
>  drivers/pci/hotplug/pciehp_core.c |  3 +++
>  drivers/pci/hotplug/pciehp_ctrl.c | 44 +++++++++++++++++++++++++++------------
>  drivers/pci/hotplug/pciehp_hpc.c  |  2 ++
>  include/linux/pci.h               |  1 +
>  5 files changed, 41 insertions(+), 14 deletions(-)
> 
> diff --git a/drivers/pci/hotplug/pciehp.h b/drivers/pci/hotplug/pciehp.h
> index 62d6fe6c3714..5047bde7d51d 100644
> --- a/drivers/pci/hotplug/pciehp.h
> +++ b/drivers/pci/hotplug/pciehp.h
> @@ -40,6 +40,7 @@
>  
>  #define MY_NAME	"pciehp"
>  
> +extern bool pciehp_poweron_delay;
>  extern bool pciehp_poll_mode;
>  extern int pciehp_poll_time;
>  extern bool pciehp_debug;
> @@ -98,6 +99,7 @@ struct controller {
>  	unsigned int cmd_busy:1;
>  	unsigned int link_active_reporting:1;
>  	unsigned int notification_enabled:1;
> +	unsigned int poweron_delay:1;	/* Delay poweron for this slot */
>  	unsigned int power_fault_detected;
>  };
>  
> @@ -112,7 +114,8 @@ struct controller {
>  #define BLINKINGON_STATE		1
>  #define BLINKINGOFF_STATE		2
>  #define POWERON_STATE			3
> -#define POWEROFF_STATE			4
> +#define DELAYED_POWERON_STATE		4
> +#define POWEROFF_STATE			5
>  
>  #define ATTN_BUTTN(ctrl)	((ctrl)->slot_cap & PCI_EXP_SLTCAP_ABP)
>  #define POWER_CTRL(ctrl)	((ctrl)->slot_cap & PCI_EXP_SLTCAP_PCP)
> diff --git a/drivers/pci/hotplug/pciehp_core.c b/drivers/pci/hotplug/pciehp_core.c
> index 612b21a14df5..cc69fd10d884 100644
> --- a/drivers/pci/hotplug/pciehp_core.c
> +++ b/drivers/pci/hotplug/pciehp_core.c
> @@ -38,6 +38,7 @@
>  #include <linux/time.h>
>  
>  /* Global variables */
> +bool pciehp_poweron_delay;
>  bool pciehp_debug;
>  bool pciehp_poll_mode;
>  int pciehp_poll_time;
> @@ -51,10 +52,12 @@ MODULE_AUTHOR(DRIVER_AUTHOR);
>  MODULE_DESCRIPTION(DRIVER_DESC);
>  MODULE_LICENSE("GPL");
>  
> +module_param(pciehp_poweron_delay, bool, 0644);
>  module_param(pciehp_debug, bool, 0644);
>  module_param(pciehp_poll_mode, bool, 0644);
>  module_param(pciehp_poll_time, int, 0644);
>  module_param(pciehp_force, bool, 0644);
> +MODULE_PARM_DESC(pciehp_poweron_delay, "Delay port power-on");
>  MODULE_PARM_DESC(pciehp_debug, "Debugging mode enabled or not");
>  MODULE_PARM_DESC(pciehp_poll_mode, "Using polling mechanism for hot-plug events or not");
>  MODULE_PARM_DESC(pciehp_poll_time, "Polling mechanism frequency, in seconds");
> diff --git a/drivers/pci/hotplug/pciehp_ctrl.c b/drivers/pci/hotplug/pciehp_ctrl.c
> index ef96a1d51fac..fd829c2b7418 100644
> --- a/drivers/pci/hotplug/pciehp_ctrl.c
> +++ b/drivers/pci/hotplug/pciehp_ctrl.c
> @@ -204,11 +204,19 @@ static void pciehp_power_thread(struct work_struct *work)
>  	kfree(info);
>  }
>  
> -void pciehp_queue_power_work(struct slot *p_slot, int req)
> +void pciehp_queue_power_work(struct slot *p_slot, int req, bool delay)
>  {
>  	struct power_work_info *info;
>  
> -	p_slot->state = req == ENABLE_REQ ? POWERON_STATE : POWEROFF_STATE;
> +	if (req == ENABLE_REQ) {
> +		p_slot->state = delay ? DELAYED_POWERON_STATE : POWERON_STATE;
> +		if (delay) {
> +			mod_delayed_work(p_slot->wq, &p_slot->work, HZ);
> +			return;
> +		}
> +	} else {
> +		p_slot->state = POWEROFF_STATE;
> +	}
>  
>  	info = kmalloc(sizeof(*info), GFP_KERNEL);
>  	if (!info) {
> @@ -229,10 +237,11 @@ void pciehp_queue_pushbutton_work(struct work_struct *work)
>  	mutex_lock(&p_slot->lock);
>  	switch (p_slot->state) {
>  	case BLINKINGOFF_STATE:
> -		pciehp_queue_power_work(p_slot, DISABLE_REQ);
> +		pciehp_queue_power_work(p_slot, DISABLE_REQ, false);
>  		break;
>  	case BLINKINGON_STATE:
> -		pciehp_queue_power_work(p_slot, ENABLE_REQ);
> +	case DELAYED_POWERON_STATE:
> +		pciehp_queue_power_work(p_slot, ENABLE_REQ, false);
>  		break;
>  	default:
>  		break;
> @@ -263,7 +272,7 @@ static void handle_button_press_event(struct slot *p_slot)
>  		/* blink green LED and turn off amber */
>  		pciehp_green_led_blink(p_slot);
>  		pciehp_set_attention_status(p_slot, 0);
> -		queue_delayed_work(p_slot->wq, &p_slot->work, 5*HZ);
> +		mod_delayed_work(p_slot->wq, &p_slot->work, 5 * HZ);
>  		break;
>  	case BLINKINGOFF_STATE:
>  	case BLINKINGON_STATE:
> @@ -285,6 +294,7 @@ static void handle_button_press_event(struct slot *p_slot)
>  		break;
>  	case POWEROFF_STATE:
>  	case POWERON_STATE:
> +	case DELAYED_POWERON_STATE:
>  		/*
>  		 * Ignore if the slot is on power-on or power-off state;
>  		 * this means that the previous attention button action
> @@ -305,12 +315,12 @@ static void handle_surprise_event(struct slot *p_slot)
>  {
>  	u8 getstatus;
>  
> +	if (p_slot->state == DELAYED_POWERON_STATE)
> +		cancel_delayed_work(&p_slot->work);
> +
>  	pciehp_get_adapter_status(p_slot, &getstatus);
> -	if (!getstatus) {
> -		pciehp_queue_power_work(p_slot, DISABLE_REQ);
> -	} else {
> -		pciehp_queue_power_work(p_slot, ENABLE_REQ);
> -	}
> +	pciehp_queue_power_work(p_slot, getstatus ? ENABLE_REQ : DISABLE_REQ,
> +				p_slot->ctrl->poweron_delay);
>  }
>  
>  /*
> @@ -327,8 +337,13 @@ static void handle_link_event(struct slot *p_slot, u32 event)
>  		/* Fall through */
>  	case STATIC_STATE:
>  		pciehp_queue_power_work(p_slot, event == INT_LINK_UP ?
> -					ENABLE_REQ : DISABLE_REQ);
> +					ENABLE_REQ : DISABLE_REQ,
> +					ctrl->poweron_delay);
>  		break;
> +	case DELAYED_POWERON_STATE:
> +		if (event != INT_LINK_UP)
> +			cancel_delayed_work(&p_slot->work);
> +		/* Fall through */
>  	case POWERON_STATE:
>  		if (event == INT_LINK_UP) {
>  			ctrl_info(ctrl,
> @@ -338,7 +353,7 @@ static void handle_link_event(struct slot *p_slot, u32 event)
>  			ctrl_info(ctrl,
>  				  "Link Down event queued on slot(%s): currently getting powered on\n",
>  				  slot_name(p_slot));
> -			pciehp_queue_power_work(p_slot, DISABLE_REQ);
> +			pciehp_queue_power_work(p_slot, DISABLE_REQ, false);
>  		}
>  		break;
>  	case POWEROFF_STATE:
> @@ -346,7 +361,8 @@ static void handle_link_event(struct slot *p_slot, u32 event)
>  			ctrl_info(ctrl,
>  				  "Link Up event queued on slot(%s): currently getting powered off\n",
>  				  slot_name(p_slot));
> -			pciehp_queue_power_work(p_slot, ENABLE_REQ);
> +			pciehp_queue_power_work(p_slot, ENABLE_REQ,
> +						ctrl->poweron_delay);
>  		} else {
>  			ctrl_info(ctrl,
>  				  "Link Down event ignored on slot(%s): already powering off\n",
> @@ -482,6 +498,7 @@ int pciehp_sysfs_enable_slot(struct slot *p_slot)
>  		p_slot->state = STATIC_STATE;
>  		break;
>  	case POWERON_STATE:
> +	case DELAYED_POWERON_STATE:
>  		ctrl_info(ctrl, "Slot %s is already in powering on state\n",
>  			  slot_name(p_slot));
>  		break;
> @@ -522,6 +539,7 @@ int pciehp_sysfs_disable_slot(struct slot *p_slot)
>  		break;
>  	case BLINKINGON_STATE:
>  	case POWERON_STATE:
> +	case DELAYED_POWERON_STATE:
>  		ctrl_info(ctrl, "Already disabled on slot %s\n",
>  			  slot_name(p_slot));
>  		break;
> diff --git a/drivers/pci/hotplug/pciehp_hpc.c b/drivers/pci/hotplug/pciehp_hpc.c
> index 5c24e938042f..7c7a598eec9f 100644
> --- a/drivers/pci/hotplug/pciehp_hpc.c
> +++ b/drivers/pci/hotplug/pciehp_hpc.c
> @@ -809,6 +809,8 @@ struct controller *pcie_init(struct pcie_device *dev)
>  	pcie_capability_read_dword(pdev, PCI_EXP_LNKCAP, &link_cap);
>  	if (link_cap & PCI_EXP_LNKCAP_DLLLARC)
>  		ctrl->link_active_reporting = 1;
> +	if (pciehp_poweron_delay || dev->port->poweron_delay)
> +		ctrl->poweron_delay = 1;
>  
>  	/* Clear all remaining event bits in Slot Status register */
>  	pcie_capability_write_word(pdev, PCI_EXP_SLTSTA,
> diff --git a/include/linux/pci.h b/include/linux/pci.h
> index e90eb22de628..9cb0fe3037b9 100644
> --- a/include/linux/pci.h
> +++ b/include/linux/pci.h
> @@ -359,6 +359,7 @@ struct pci_dev {
>  	unsigned int	io_window_1k:1;	/* Intel P2P bridge 1K I/O windows */
>  	unsigned int	irq_managed:1;
>  	unsigned int	has_secondary_link:1;
> +	unsigned int    poweron_delay:1;	/* Port needs poweron delay */
>  	pci_dev_flags_t dev_flags;
>  	atomic_t	enable_cnt;	/* pci_enable_device has been called */
>  
> -- 
> 2.1.4
> 
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