libata: retry link resume if necessary

Interestingly, when SIDPR is used in ata_piix, writes to DET in
SControl sometimes get ignored leading to detection failure.  Update
sata_link_resume() such that it reads back SControl after clearing DET
and retry if it's not clear.

Signed-off-by: Tejun Heo <tj@kernel.org>
Reported-by: fengxiangjun <fengxiangjun@neusoft.com>
Reported-by: Jim Faulkner <jfaulkne@ccs.neu.edu>
Cc: stable@kernel.org
Signed-off-by: Jeff Garzik <jgarzik@redhat.com>

2 files changed, 34 insertions, 7 deletions

diff --git a/drivers/ata/libata-core.c b/drivers/ata/libata-core.c
index 22ff51bdbc8a..6728328f3bea 100644
--- a/drivers/ata/libata-core.c
+++ b/drivers/ata/libata-core.c
@@ -3790,21 +3790,45 @@ int sata_link_debounce(struct ata_link *link, const unsigned long *params,
 int sata_link_resume(struct ata_link *link, const unsigned long *params,
                      unsigned long deadline)
 {
+        int tries = ATA_LINK_RESUME_TRIES;
         u32 scontrol, serror;
         int rc;
 
         if ((rc = sata_scr_read(link, SCR_CONTROL, &scontrol)))
                 return rc;
 
-        scontrol = (scontrol & 0x0f0) | 0x300;
+        /*
+         * Writes to SControl sometimes get ignored under certain
+         * controllers (ata_piix SIDPR).  Make sure DET actually is
+         * cleared.
+         */
+        do {
+                scontrol = (scontrol & 0x0f0) | 0x300;
+                if ((rc = sata_scr_write(link, SCR_CONTROL, scontrol)))
+                        return rc;
+                /*
+                 * Some PHYs react badly if SStatus is pounded
+                 * immediately after resuming.  Delay 200ms before
+                 * debouncing.
+                 */
+                msleep(200);
 
-        if ((rc = sata_scr_write(link, SCR_CONTROL, scontrol)))
-                return rc;
+                /* is SControl restored correctly? */
+                if ((rc = sata_scr_read(link, SCR_CONTROL, &scontrol)))
+                        return rc;
+        } while ((scontrol & 0xf0f) != 0x300 && --tries);
 
-        /* Some PHYs react badly if SStatus is pounded immediately
-         * after resuming.  Delay 200ms before debouncing.
-         */
-        msleep(200);
+        if ((scontrol & 0xf0f) != 0x300) {
+                ata_link_printk(link, KERN_ERR,
+                                "failed to resume link (SControl %X)\n",
+                                scontrol);
+                return 0;
+        }
+
+        if (tries < ATA_LINK_RESUME_TRIES)
+                ata_link_printk(link, KERN_WARNING,
+                                "link resume succeeded after %d retries\n",
+                                ATA_LINK_RESUME_TRIES - tries);
 
         if ((rc = sata_link_debounce(link, params, deadline)))
                 return rc;
diff --git a/include/linux/libata.h b/include/linux/libata.h
index 6a9c4ddd3d95..73112250862c 100644
--- a/include/linux/libata.h
+++ b/include/linux/libata.h
@@ -354,6 +354,9 @@ enum {
         /* max tries if error condition is still set after ->error_handler */
         ATA_EH_MAX_TRIES        = 5,
 
+        /* sometimes resuming a link requires several retries */
+        ATA_LINK_RESUME_TRIES   = 5,
+
         /* how hard are we gonna try to probe/recover devices */
         ATA_PROBE_MAX_TRIES     = 3,
         ATA_EH_DEV_TRIES        = 3,