Re: [PATCH v2 2/4] pciehp: Use link change notifications for hot-plug and removal

Bjorn Helgaas
2013-12-12T22:44:15Z

[+cc Yinghai]

On Tue, Dec 03, 2013 at 02:32:46PM -0800, Rajat Jain wrote:
> A lot of systems do not have the fancy buttons and LEDs, and instead
> want to rely only on the Link state change events to drive the hotplug
> and removal state machinery.
> (http://www.spinics.net/lists/hotplug/msg05802.html)
>
> This patch adds support for that functionality. Here are the details
> about the patch itself:
>
> * Define and use interrupt events for linkup / linkdown.

This seems like a reasonable idea.

In the ExpressCard Standard (Rel 2.0, Feb 2009), Section 6.3.1 and Figure
6-2 talk about a "Link Detect" or "Link Train Detected" interrupt being
used to trigger the ACPI hotplug flow for a non-PCIe-aware OS. I'm not
sure what interrupt this refers to. The Slot Control Data Link Layer State
Changed interrupt (which you're using) sounds similar, but my guess is that
"Link Detect" is a generic term for chipset-specific functionality to
generate an SMI for hotplug events.

But then Section 6.3.1.1 suggests that a PCIe-aware OS would use "Presence
Detect Changed" instead. I don't know why a different mechanism would be
suggested, although DLLSC was added after PCIe 1.0, so older hardware
wouldn't have a PCIe-standard link detection mechanism.

In any event, I think having the Link Status Data Link Layer Link Active
bit set would certainly imply that a device is present, so it seems
reasonable to use DLLLA in addition to Presence Detect State.

> * Introduce the functions to handle link-up and link-down events and
> queue the work in the slot->wq to be processed by pciehp_power_thread
>
> * The current code bails out from device removal, if an adapter is not
> detected. That is not right, because if an adapter is not present at
> all, it provides all the more reason to REMOVE the device. This is
> specially a problem for link state hot-plug, because some ports use
> in band mechanism to detect the presence detection. Thus when link
> goes down, presence detect also goes down. We _want_ that the devices
> should be removed in this case.
>
> * The current pciehp driver disabled the link in case of a hot-removal.
> Since for link change based hot-plug to work, we need that enabled,
> hence make sure to not disable the link permanently if link state
> based hot-plug is to be used. Also have to remove
> pciehp_link_disable() and pcie_wait_link_not_active() static functions
> since they are not being used anywhere else.
>
> * pciehp_reset_slot - reset of secondary bus may cause undesirable
> spurious link notifications. Thus disable these around the secondary
> bus reset.
>
> Signed-off-by: Rajat Jain <rajatjain@juniper.net>
> Signed-off-by: Guenter Roeck <groeck@juniper.net>
> ---
> v2: - drop the use_link_state_events module parameter as discussed here:
> http://marc.info/?t=138513966800006&r=1&w=2
> - removed the static functions left unused after this patch.
> - make the pciehp_handle_linkstate_change() return void.
> - dropped the "RFC" from subject, and added Guenter's signature
>
> drivers/pci/hotplug/pciehp.h | 3 +
> drivers/pci/hotplug/pciehp_ctrl.c | 130 ++++++++++++++++++++++++++++++++++---
> drivers/pci/hotplug/pciehp_hpc.c | 56 ++++++++--------
> 3 files changed, 150 insertions(+), 39 deletions(-)
>
> diff --git a/drivers/pci/hotplug/pciehp.h b/drivers/pci/hotplug/pciehp.h
> index fc322ed..353edda 100644
> --- a/drivers/pci/hotplug/pciehp.h
> +++ b/drivers/pci/hotplug/pciehp.h
> @@ -110,6 +110,8 @@ struct controller {
> #define INT_BUTTON_PRESS 7
> #define INT_BUTTON_RELEASE 8
> #define INT_BUTTON_CANCEL 9
> +#define INT_LINK_UP 10
> +#define INT_LINK_DOWN 11
>
> #define STATIC_STATE 0
> #define BLINKINGON_STATE 1
> @@ -133,6 +135,7 @@ u8 pciehp_handle_attention_button(struct slot *p_slot);
> u8 pciehp_handle_switch_change(struct slot *p_slot);
> u8 pciehp_handle_presence_change(struct slot *p_slot);
> u8 pciehp_handle_power_fault(struct slot *p_slot);
> +void pciehp_handle_linkstate_change(struct slot *p_slot);
> int pciehp_configure_device(struct slot *p_slot);
> int pciehp_unconfigure_device(struct slot *p_slot);
> void pciehp_queue_pushbutton_work(struct work_struct *work);
> diff --git a/drivers/pci/hotplug/pciehp_ctrl.c b/drivers/pci/hotplug/pciehp_ctrl.c
> index 38f0186..4c2544c 100644
> --- a/drivers/pci/hotplug/pciehp_ctrl.c
> +++ b/drivers/pci/hotplug/pciehp_ctrl.c
> @@ -150,6 +150,27 @@ u8 pciehp_handle_power_fault(struct slot *p_slot)
> return 1;
> }
>
> +void pciehp_handle_linkstate_change(struct slot *p_slot)
> +{
> + u32 event_type;
> + struct controller *ctrl = p_slot->ctrl;
> +
> + /* Link Status Change */
> + ctrl_dbg(ctrl, "Data Link Layer State change\n");
> +
> + if (pciehp_check_link_active(ctrl)) {
> + ctrl_info(ctrl, "slot(%s): Link Up event\n",
> + slot_name(p_slot));
> + event_type = INT_LINK_UP;
> + } else {
> + ctrl_info(ctrl, "slot(%s): Link Down event\n",
> + slot_name(p_slot));
> + event_type = INT_LINK_DOWN;
> + }
> +
> + queue_interrupt_event(p_slot, event_type);
> +}
> +
> /* The following routines constitute the bulk of the
> hotplug controller logic
> */
> @@ -442,6 +463,100 @@ static void handle_surprise_event(struct slot *p_slot)
> queue_work(p_slot->wq, &info->work);
> }
>
> +/*
> + * Note: This function must be called with slot->lock held
> + */
> +static void handle_link_up_event(struct slot *p_slot)
> +{
> + struct controller *ctrl = p_slot->ctrl;
> + struct power_work_info *info;
> +
> + info = kmalloc(sizeof(*info), GFP_KERNEL);
> + if (!info) {
> + ctrl_err(p_slot->ctrl, "%s: Cannot allocate memory\n",
> + __func__);
> + return;
> + }
> + info->p_slot = p_slot;
> + INIT_WORK(&info->work, pciehp_power_thread);
> +
> + switch (p_slot->state) {
> + case BLINKINGON_STATE:
> + case BLINKINGOFF_STATE:
> + cancel_delayed_work(&p_slot->work);
> + /* Fall through */
> + case STATIC_STATE:
> + p_slot->state = POWERON_STATE;
> + queue_work(p_slot->wq, &info->work);
> + break;
> + case POWERON_STATE:
> + ctrl_info(ctrl,
> + "Link Up event ignored on slot(%s): already powering on\n",
> + slot_name(p_slot));
> + kfree(info);
> + break;
> + case POWEROFF_STATE:
> + ctrl_info(ctrl,
> + "Link Up event queued on slot(%s): currently getting powered off\n",
> + slot_name(p_slot));
> + p_slot->state = POWERON_STATE;
> + queue_work(p_slot->wq, &info->work);
> + break;
> + default:
> + ctrl_err(ctrl, "Not a valid state on slot(%s)\n",
> + slot_name(p_slot));
> + kfree(info);
> + break;
> + }
> +}
> +
> +/*
> + * Note: This function must be called with slot->lock held
> + */
> +static void handle_link_down_event(struct slot *p_slot)
> +{
> + struct controller *ctrl = p_slot->ctrl;
> + struct power_work_info *info;
> +
> + info = kmalloc(sizeof(*info), GFP_KERNEL);
> + if (!info) {
> + ctrl_err(p_slot->ctrl, "%s: Cannot allocate memory\n",
> + __func__);
> + return;
> + }
> + info->p_slot = p_slot;
> + INIT_WORK(&info->work, pciehp_power_thread);
> +
> + switch (p_slot->state) {
> + case BLINKINGON_STATE:
> + case BLINKINGOFF_STATE:
> + cancel_delayed_work(&p_slot->work);
> + /* Fall through */
> + case STATIC_STATE:
> + p_slot->state = POWEROFF_STATE;
> + queue_work(p_slot->wq, &info->work);
> + break;
> + case POWEROFF_STATE:
> + ctrl_info(ctrl,
> + "Link Down event ignored on slot(%s): already powering off\n",
> + slot_name(p_slot));
> + kfree(info);
> + break;
> + case POWERON_STATE:
> + ctrl_info(ctrl,
> + "Link Down event queued on slot(%s): currently getting powered on\n",
> + slot_name(p_slot));
> + p_slot->state = POWEROFF_STATE;
> + queue_work(p_slot->wq, &info->work);
> + break;
> + default:
> + ctrl_err(ctrl, "Not a valid state on slot %s\n",
> + slot_name(p_slot));
> + kfree(info);
> + break;
> + }
> +}
> +
> static void interrupt_event_handler(struct work_struct *work)
> {
> struct event_info *info = container_of(work, struct event_info, work);
> @@ -468,6 +583,12 @@ static void interrupt_event_handler(struct work_struct *work)
> ctrl_dbg(ctrl, "Surprise Removal\n");
> handle_surprise_event(p_slot);
> break;
> + case INT_LINK_UP:
> + handle_link_up_event(p_slot);
> + break;
> + case INT_LINK_DOWN:
> + handle_link_down_event(p_slot);
> + break;
> default:
> break;
> }
> @@ -524,15 +645,6 @@ int pciehp_disable_slot(struct slot *p_slot)
> if (!p_slot->ctrl)
> return 1;
>
> - if (!HP_SUPR_RM(p_slot->ctrl)) {
> - ret = pciehp_get_adapter_status(p_slot, &getstatus);
> - if (ret || !getstatus) {
> - ctrl_info(ctrl, "No adapter on slot(%s)\n",
> - slot_name(p_slot));
> - return -ENODEV;
> - }
> - }
> -

This seems like a candidate for splitting into a separate patch.

> if (MRL_SENS(p_slot->ctrl)) {
> ret = pciehp_get_latch_status(p_slot, &getstatus);
> if (ret || getstatus) {
> diff --git a/drivers/pci/hotplug/pciehp_hpc.c b/drivers/pci/hotplug/pciehp_hpc.c
> index 3a5eee7..1f152f3 100644
> --- a/drivers/pci/hotplug/pciehp_hpc.c
> +++ b/drivers/pci/hotplug/pciehp_hpc.c
> @@ -278,11 +278,6 @@ static void pcie_wait_link_active(struct controller *ctrl)
> __pcie_wait_link_active(ctrl, true);
> }
>
> -static void pcie_wait_link_not_active(struct controller *ctrl)
> -{
> - __pcie_wait_link_active(ctrl, false);
> -}
> -
> static bool pci_bus_check_dev(struct pci_bus *bus, int devfn)
> {
> u32 l;
> @@ -383,11 +378,6 @@ static int pciehp_link_enable(struct controller *ctrl)
> return __pciehp_link_set(ctrl, true);
> }
>
> -static int pciehp_link_disable(struct controller *ctrl)
> -{
> - return __pciehp_link_set(ctrl, false);
> -}
> -
> int pciehp_get_attention_status(struct slot *slot, u8 *status)
> {
> struct controller *ctrl = slot->ctrl;
> @@ -620,13 +610,10 @@ int pciehp_power_off_slot(struct slot * slot)
> u16 cmd_mask;
> int retval;
>
> - /* Disable the link at first */
> - pciehp_link_disable(ctrl);
> - /* wait the link is down */
> - if (ctrl->link_active_reporting)
> - pcie_wait_link_not_active(ctrl);
> - else
> - msleep(1000);

2debd9289997 ("PCI: pciehp: Disable/enable link during slot power off/on")
added this code that disables the link to fix problems. So we need to make
sure we don't reintroduce those problems by leaving the link enabled.

One problem was spurious "card present/not present" messages. I suspect
that topology has an attention button, and I'm not sure it makes sense to
enable the presence detect interrupt in that case. As far as I can tell,
if there's an attention button, the OS should not do anything on card
insertion or removal; it should only do something when the attention button
is pressed. So maybe we can deal with the message issue that way.

The changelog also hints that disabling the link might be needed to allow a
repeater to be reset, but I don't know the details. I don't remember any
spec language that requires the link to be disabled on hotplug; maybe this
is a platform-specific quirk.

This patch is pretty large and if it could be split up a bit, especially
this particular part, it might help Yinghai verify that his system keeps
working.

Bjorn

> + /*
> + * We do not disable the link, since a future link-up event can now
> + * be used to initiate hot-plug
> + */
>
> slot_cmd = POWER_OFF;
> cmd_mask = PCI_EXP_SLTCTL_PCC;
> @@ -661,7 +648,7 @@ static irqreturn_t pcie_isr(int irq, void *dev_id)
>
> detected &= (PCI_EXP_SLTSTA_ABP | PCI_EXP_SLTSTA_PFD |
> PCI_EXP_SLTSTA_MRLSC | PCI_EXP_SLTSTA_PDC |
> - PCI_EXP_SLTSTA_CC);
> + PCI_EXP_SLTSTA_CC | PCI_EXP_SLTSTA_DLLSC);
> detected &= ~intr_loc;
> intr_loc |= detected;
> if (!intr_loc)
> @@ -702,6 +689,10 @@ static irqreturn_t pcie_isr(int irq, void *dev_id)
> ctrl->power_fault_detected = 1;
> pciehp_handle_power_fault(slot);
> }
> +
> + if (intr_loc & PCI_EXP_SLTSTA_DLLSC)
> + pciehp_handle_linkstate_change(slot);
> +
> return IRQ_HANDLED;
> }
>
> @@ -719,7 +710,7 @@ int pcie_enable_notification(struct controller *ctrl)
> * when it is cleared in the interrupt service routine, and
> * next power fault detected interrupt was notified again.
> */
> - cmd = PCI_EXP_SLTCTL_PDCE;
> + cmd = PCI_EXP_SLTCTL_PDCE | PCI_EXP_SLTCTL_DLLSCE;
> if (ATTN_BUTTN(ctrl))
> cmd |= PCI_EXP_SLTCTL_ABPE;
> if (MRL_SENS(ctrl))
> @@ -751,31 +742,36 @@ static void pcie_disable_notification(struct controller *ctrl)
>
> /*
> * pciehp has a 1:1 bus:slot relationship so we ultimately want a secondary
> - * bus reset of the bridge, but if the slot supports surprise removal we need
> - * to disable presence detection around the bus reset and clear any spurious
> + * bus reset of the bridge, but if the slot supports surprise removal (or
> + * link state change based hotplug), we need to disable presence detection
> + * (or link state notifications) around the bus reset and clear any spurious
> * events after.
> */
> int pciehp_reset_slot(struct slot *slot, int probe)
> {
> struct controller *ctrl = slot->ctrl;
> + u16 stat_mask = 0, ctrl_mask = 0;
>
> if (probe)
> return 0;
>
> if (HP_SUPR_RM(ctrl)) {
> - pcie_write_cmd(ctrl, 0, PCI_EXP_SLTCTL_PDCE);
> - if (pciehp_poll_mode)
> - del_timer_sync(&ctrl->poll_timer);
> + ctrl_mask |= PCI_EXP_SLTCTL_PDCE;
> + stat_mask |= PCI_EXP_SLTSTA_PDC;
> }
> + ctrl_mask |= PCI_EXP_SLTCTL_DLLSCE;
> + stat_mask |= PCI_EXP_SLTSTA_DLLSC;
> +
> + pcie_write_cmd(ctrl, 0, ctrl_mask);
> + if (pciehp_poll_mode)
> + del_timer_sync(&ctrl->poll_timer);
>
> pci_reset_bridge_secondary_bus(ctrl->pcie->port);
>
> - if (HP_SUPR_RM(ctrl)) {
> - pciehp_writew(ctrl, PCI_EXP_SLTSTA, PCI_EXP_SLTSTA_PDC);
> - pcie_write_cmd(ctrl, PCI_EXP_SLTCTL_PDCE, PCI_EXP_SLTCTL_PDCE);
> - if (pciehp_poll_mode)
> - int_poll_timeout(ctrl->poll_timer.data);
> - }
> + pciehp_writew(ctrl, PCI_EXP_SLTSTA, stat_mask);
> + pcie_write_cmd(ctrl, ctrl_mask, ctrl_mask);
> + if (pciehp_poll_mode)
> + int_poll_timeout(ctrl->poll_timer.data);
>
> return 0;
> }
> --
> 1.7.9.5
>