NTB: BWD Link Recovery

The BWD NTB device will drop the link if an error is encountered on the
point-to-point PCI bridge.  The link will stay down until all errors are
cleared and the link is re-established.  On link down, check to see if
the error is detected, if so do the necessary housekeeping to try and
recover from the error and reestablish the link.

There is a potential race between the 2 NTB devices recovering at the
same time.  If the times are synchronized, the link will not recover and the
driver will be stuck in this loop forever.  Add a random interval to the
recovery time to prevent this race.

Signed-off-by: Jon Mason <jon.mason@intel.com>

3 files changed, 127 insertions, 3 deletions

diff --git a/drivers/ntb/ntb_hw.c b/drivers/ntb/ntb_hw.c
index 226f82b7da65..3493e9516519 100644
--- a/drivers/ntb/ntb_hw.c
+++ b/drivers/ntb/ntb_hw.c
@@ -46,10 +46,12 @@
  * Jon Mason <jon.mason@intel.com>
  */
 #include <linux/debugfs.h>
+#include <linux/delay.h>
 #include <linux/init.h>
 #include <linux/interrupt.h>
 #include <linux/module.h>
 #include <linux/pci.h>
+#include <linux/random.h>
 #include <linux/slab.h>
 #include "ntb_hw.h"
 #include "ntb_regs.h"
@@ -84,6 +86,8 @@ enum {
 
 static struct dentry *debugfs_dir;
 
+#define BWD_LINK_RECOVERY_TIME  500
+
 /* Translate memory window 0,1 to BAR 2,4 */
 #define MW_TO_BAR(mw)   (mw * NTB_MAX_NUM_MW + 2)
 
@@ -425,6 +429,49 @@ void ntb_ring_sdb(struct ntb_device *ndev, unsigned int db)
                        (db * ndev->bits_per_vector), ndev->reg_ofs.sdb);
 }
 
+static void bwd_recover_link(struct ntb_device *ndev)
+{
+        u32 status;
+
+        /* Driver resets the NTB ModPhy lanes - magic! */
+        writeb(0xe0, ndev->reg_base + BWD_MODPHY_PCSREG6);
+        writeb(0x40, ndev->reg_base + BWD_MODPHY_PCSREG4);
+        writeb(0x60, ndev->reg_base + BWD_MODPHY_PCSREG4);
+        writeb(0x60, ndev->reg_base + BWD_MODPHY_PCSREG6);
+
+        /* Driver waits 100ms to allow the NTB ModPhy to settle */
+        msleep(100);
+
+        /* Clear AER Errors, write to clear */
+        status = readl(ndev->reg_base + BWD_ERRCORSTS_OFFSET);
+        dev_dbg(&ndev->pdev->dev, "ERRCORSTS = %x\n", status);
+        status &= PCI_ERR_COR_REP_ROLL;
+        writel(status, ndev->reg_base + BWD_ERRCORSTS_OFFSET);
+
+        /* Clear unexpected electrical idle event in LTSSM, write to clear */
+        status = readl(ndev->reg_base + BWD_LTSSMERRSTS0_OFFSET);
+        dev_dbg(&ndev->pdev->dev, "LTSSMERRSTS0 = %x\n", status);
+        status |= BWD_LTSSMERRSTS0_UNEXPECTEDEI;
+        writel(status, ndev->reg_base + BWD_LTSSMERRSTS0_OFFSET);
+
+        /* Clear DeSkew Buffer error, write to clear */
+        status = readl(ndev->reg_base + BWD_DESKEWSTS_OFFSET);
+        dev_dbg(&ndev->pdev->dev, "DESKEWSTS = %x\n", status);
+        status |= BWD_DESKEWSTS_DBERR;
+        writel(status, ndev->reg_base + BWD_DESKEWSTS_OFFSET);
+
+        status = readl(ndev->reg_base + BWD_IBSTERRRCRVSTS0_OFFSET);
+        dev_dbg(&ndev->pdev->dev, "IBSTERRRCRVSTS0 = %x\n", status);
+        status &= BWD_IBIST_ERR_OFLOW;
+        writel(status, ndev->reg_base + BWD_IBSTERRRCRVSTS0_OFFSET);
+
+        /* Releases the NTB state machine to allow the link to retrain */
+        status = readl(ndev->reg_base + BWD_LTSSMSTATEJMP_OFFSET);
+        dev_dbg(&ndev->pdev->dev, "LTSSMSTATEJMP = %x\n", status);
+        status &= ~BWD_LTSSMSTATEJMP_FORCEDETECT;
+        writel(status, ndev->reg_base + BWD_LTSSMSTATEJMP_OFFSET);
+}
+
 static void ntb_link_event(struct ntb_device *ndev, int link_state)
 {
         unsigned int event;
@@ -448,13 +495,16 @@ static void ntb_link_event(struct ntb_device *ndev, int link_state)
                         if (rc)
                                 return;
                 }
+
+                ndev->link_width = (status & NTB_LINK_WIDTH_MASK) >> 4;
+                ndev->link_speed = (status & NTB_LINK_SPEED_MASK);
                 dev_info(&ndev->pdev->dev, "Link Width %d, Link Speed %d\n",
-                         (status & NTB_LINK_WIDTH_MASK) >> 4,
-                         (status & NTB_LINK_SPEED_MASK));
+                         ndev->link_width, ndev->link_speed);
         } else {
                 dev_info(&ndev->pdev->dev, "Link Down\n");
                 ndev->link_status = NTB_LINK_DOWN;
                 event = NTB_EVENT_HW_LINK_DOWN;
+                /* Don't modify link width/speed, we need it in link recovery */
         }
 
         /* notify the upper layer if we have an event change */
@@ -494,6 +544,47 @@ static int ntb_link_status(struct ntb_device *ndev)
         return 0;
 }
 
+static void bwd_link_recovery(struct work_struct *work)
+{
+        struct ntb_device *ndev = container_of(work, struct ntb_device,
+                                               lr_timer.work);
+        u32 status32;
+
+        bwd_recover_link(ndev);
+        /* There is a potential race between the 2 NTB devices recovering at the
+         * same time.  If the times are the same, the link will not recover and
+         * the driver will be stuck in this loop forever.  Add a random interval
+         * to the recovery time to prevent this race.
+         */
+        msleep(BWD_LINK_RECOVERY_TIME + prandom_u32() % BWD_LINK_RECOVERY_TIME);
+
+        status32 = readl(ndev->reg_base + BWD_LTSSMSTATEJMP_OFFSET);
+        if (status32 & BWD_LTSSMSTATEJMP_FORCEDETECT)
+                goto retry;
+
+        status32 = readl(ndev->reg_base + BWD_IBSTERRRCRVSTS0_OFFSET);
+        if (status32 & BWD_IBIST_ERR_OFLOW)
+                goto retry;
+
+        status32 = readl(ndev->reg_ofs.lnk_cntl);
+        if (!(status32 & BWD_CNTL_LINK_DOWN)) {
+                unsigned char speed, width;
+                u16 status16;
+
+                status16 = readw(ndev->reg_ofs.lnk_stat);
+                width = (status16 & NTB_LINK_WIDTH_MASK) >> 4;
+                speed = (status16 & NTB_LINK_SPEED_MASK);
+                if (ndev->link_width != width || ndev->link_speed != speed)
+                        goto retry;
+        }
+
+        schedule_delayed_work(&ndev->hb_timer, NTB_HB_TIMEOUT);
+        return;
+
+retry:
+        schedule_delayed_work(&ndev->lr_timer, NTB_HB_TIMEOUT);
+}
+
 /* BWD doesn't have link status interrupt, poll on that platform */
 static void bwd_link_poll(struct work_struct *work)
 {
@@ -509,6 +600,16 @@ static void bwd_link_poll(struct work_struct *work)
                 if (rc)
                         dev_err(&ndev->pdev->dev,
                                 "Error determining link status\n");
+
+                /* Check to see if a link error is the cause of the link down */
+                if (ndev->link_status == NTB_LINK_DOWN) {
+                        u32 status32 = readl(ndev->reg_base +
+                                             BWD_LTSSMSTATEJMP_OFFSET);
+                        if (status32 & BWD_LTSSMSTATEJMP_FORCEDETECT) {
+                                schedule_delayed_work(&ndev->lr_timer, 0);
+                                return;
+                        }
+                }
         }
 
         schedule_delayed_work(&ndev->hb_timer, NTB_HB_TIMEOUT);
@@ -703,6 +804,7 @@ static int ntb_bwd_setup(struct ntb_device *ndev)
 
         /* Since bwd doesn't have a link interrupt, setup a poll timer */
         INIT_DELAYED_WORK(&ndev->hb_timer, bwd_link_poll);
+        INIT_DELAYED_WORK(&ndev->lr_timer, bwd_link_recovery);
         schedule_delayed_work(&ndev->hb_timer, NTB_HB_TIMEOUT);
 
         return 0;
@@ -743,8 +845,10 @@ static int ntb_device_setup(struct ntb_device *ndev)
 
 static void ntb_device_free(struct ntb_device *ndev)
 {
-        if (ndev->hw_type == BWD_HW)
+        if (ndev->hw_type == BWD_HW) {
                 cancel_delayed_work_sync(&ndev->hb_timer);
+                cancel_delayed_work_sync(&ndev->lr_timer);
+        }
 }
 
 static irqreturn_t bwd_callback_msix_irq(int irq, void *data)
diff --git a/drivers/ntb/ntb_hw.h b/drivers/ntb/ntb_hw.h
index 72fcb22d7dd8..3a15d492593c 100644
--- a/drivers/ntb/ntb_hw.h
+++ b/drivers/ntb/ntb_hw.h
@@ -125,10 +125,15 @@ struct ntb_device {
         unsigned char num_msix;
         unsigned char bits_per_vector;
         unsigned char max_cbs;
+        unsigned char link_width;
+        unsigned char link_speed;
         unsigned char link_status;
+
         struct delayed_work hb_timer;
         unsigned long last_ts;
 
+        struct delayed_work lr_timer;
+
         struct dentry *debugfs_dir;
 };
 
diff --git a/drivers/ntb/ntb_regs.h b/drivers/ntb/ntb_regs.h
index 4ddc590d03a6..03a66ef32a68 100644
--- a/drivers/ntb/ntb_regs.h
+++ b/drivers/ntb/ntb_regs.h
@@ -115,6 +115,7 @@
 #define BWD_MBAR45_OFFSET       0xb020
 #define BWD_DEVCTRL_OFFSET      0xb048
 #define BWD_LINK_STATUS_OFFSET  0xb052
+#define BWD_ERRCORSTS_OFFSET    0xb110
 
 #define BWD_SBAR2XLAT_OFFSET    0x0008
 #define BWD_SBAR4XLAT_OFFSET    0x0010
@@ -132,6 +133,20 @@
 #define BWD_B2B_SPADSEMA_OFFSET 0x80c0
 #define BWD_B2B_STKYSPAD_OFFSET 0x80c4
 
+#define BWD_MODPHY_PCSREG4      0x1c004
+#define BWD_MODPHY_PCSREG6      0x1c006
+
+#define BWD_IP_BASE             0xC000
+#define BWD_DESKEWSTS_OFFSET    (BWD_IP_BASE + 0x3024)
+#define BWD_LTSSMERRSTS0_OFFSET (BWD_IP_BASE + 0x3180)
+#define BWD_LTSSMSTATEJMP_OFFSET        (BWD_IP_BASE + 0x3040)
+#define BWD_IBSTERRRCRVSTS0_OFFSET      (BWD_IP_BASE + 0x3324)
+
+#define BWD_DESKEWSTS_DBERR     (1 << 15)
+#define BWD_LTSSMERRSTS0_UNEXPECTEDEI   (1 << 20)
+#define BWD_LTSSMSTATEJMP_FORCEDETECT   (1 << 2)
+#define BWD_IBIST_ERR_OFLOW     0x7FFF7FFF
+
 #define NTB_CNTL_BAR23_SNOOP    (1 << 2)
 #define NTB_CNTL_BAR45_SNOOP    (1 << 6)
 #define BWD_CNTL_LINK_DOWN      (1 << 16)