platform/x86/intel/sdsi: Handle leaky bucket

To prevent an agent from indefinitely holding the mailbox firmware has
implemented a leaky bucket algorithm. Repeated access to the mailbox may
now incur a delay of up to 2.1 seconds. Add a retry loop that tries for
up to 2.5 seconds to acquire the mailbox.

Fixes: 2546c6000430 ("platform/x86: Add Intel Software Defined Silicon driver")
Signed-off-by: David E. Box <david.e.box@linux.intel.com>
Link: https://lore.kernel.org/r/20220420155622.1763633-2-david.e.box@linux.intel.com
Reviewed-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>

diff --git a/drivers/platform/x86/intel/sdsi.c b/drivers/platform/x86/intel/sdsi.c
index 11d14cc..11f2114 100644 (file)
--- a/drivers/platform/x86/intel/sdsi.c
+++ b/drivers/platform/x86/intel/sdsi.c
@@ -51,6 +51,8 @@
 #define MBOX_TIMEOUT_US                        2000
 #define MBOX_TIMEOUT_ACQUIRE_US                1000
 #define MBOX_POLLING_PERIOD_US         100
+#define MBOX_ACQUIRE_NUM_RETRIES       5
+#define MBOX_ACQUIRE_RETRY_DELAY_MS    500
 #define MBOX_MAX_PACKETS               4
 
 #define MBOX_OWNER_NONE                        0x00
@@ -263,7 +265,7 @@ static int sdsi_mbox_acquire(struct sdsi_priv *priv, struct sdsi_mbox_info *info
 {
        u64 control;
        u32 owner;
-       int ret;
+       int ret, retries = 0;
 
        lockdep_assert_held(&priv->mb_lock);
 
@@ -273,13 +275,29 @@ static int sdsi_mbox_acquire(struct sdsi_priv *priv, struct sdsi_mbox_info *info
        if (owner != MBOX_OWNER_NONE)
                return -EBUSY;
 
-       /* Write first qword of payload */
-       writeq(info->payload[0], priv->mbox_addr);
+       /*
+        * If there has been no recent transaction and no one owns the mailbox,
+        * we should acquire it in under 1ms. However, if we've accessed it
+        * recently it may take up to 2.1 seconds to acquire it again.
+        */
+       do {
+               /* Write first qword of payload */
+               writeq(info->payload[0], priv->mbox_addr);
+
+               /* Check for ownership */
+               ret = readq_poll_timeout(priv->control_addr, control,
+                       FIELD_GET(CTRL_OWNER, control) == MBOX_OWNER_INBAND,
+                       MBOX_POLLING_PERIOD_US, MBOX_TIMEOUT_ACQUIRE_US);
+
+               if (FIELD_GET(CTRL_OWNER, control) == MBOX_OWNER_NONE &&
+                   retries++ < MBOX_ACQUIRE_NUM_RETRIES) {
+                       msleep(MBOX_ACQUIRE_RETRY_DELAY_MS);
+                       continue;
+               }
 
-       /* Check for ownership */
-       ret = readq_poll_timeout(priv->control_addr, control,
-                                FIELD_GET(CTRL_OWNER, control) & MBOX_OWNER_INBAND,
-                                MBOX_POLLING_PERIOD_US, MBOX_TIMEOUT_ACQUIRE_US);
+               /* Either we got it or someone else did. */
+               break;
+       } while (true);
 
        return ret;
 }