ice: check Tx timestamp memory register for ready timestamps

The PHY for E822 based hardware has a register which indicates which
timestamps are valid in the PHY timestamp memory block. Each bit in the
register indicates whether the associated index in the timestamp memory is
valid.

Hardware sets this bit when the timestamp is captured, and clears the bit
when the timestamp is read. Use of this register is important as reading
timestamp registers can impact the way that hardware generates timestamp
interrupts.

This occurs because the PHY has an internal value which is incremented
when hardware captures a timestamp and decremented when software reads a
timestamp. Reading timestamps which are not marked as valid still decrement
the internal value and can result in the Tx timestamp interrupt not
triggering in the future.

To prevent this, use the timestamp memory value to determine which
timestamps are ready to be read. The ice_get_phy_tx_tstamp_ready function
reads this value. For E810 devices, this just always returns with all bits
set.

Skip any timestamp which is not set in this bitmap, avoiding reading extra
timestamps on E822 devices.

The stale check against a cached timestamp value is no longer necessary for
PHYs which support the timestamp ready bitmap properly. E810 devices still
need this. Introduce a new verify_cached flag to the ice_ptp_tx structure.
Use this to determine if we need to perform the verification against the
cached timestamp value. Set this to 1 for the E810 Tx tracker init
function. Notice that many of the fields in ice_ptp_tx are simple 1 bit
flags. Save some structure space by using bitfields of length 1 for these
values.

Modify the ICE_PTP_TS_VALID check to simply drop the timestamp immediately
so that in an event of getting such an invalid timestamp the driver does
not attempt to re-read the timestamp again in a future poll of the
register.

With these changes, the driver now reads each timestamp register exactly
once, and does not attempt any re-reads. This ensures the interrupt
tracking logic in the PHY will not get stuck.

Signed-off-by: Jacob Keller <jacob.e.keller@intel.com>
Tested-by: Gurucharan G <gurucharanx.g@intel.com> (A Contingent worker at Intel)
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>

1 files changed, 12 insertions, 5 deletions

diff --git a/drivers/net/ethernet/intel/ice/ice_ptp.h b/drivers/net/ethernet/intel/ice/ice_ptp.h
index 39cab020f1af..5052fc41bed3 100644
--- a/drivers/net/ethernet/intel/ice/ice_ptp.h
+++ b/drivers/net/ethernet/intel/ice/ice_ptp.h
@@ -93,9 +93,14 @@ struct ice_perout_channel {
  * we discard old requests that were not fulfilled within a 2 second time
  * window.
  * Timestamp values in the PHY are read only and do not get cleared except at
- * hardware reset or when a new timestamp value is captured. The cached_tstamp
- * field is used to detect the case where a new timestamp has not yet been
- * captured, ensuring that we avoid sending stale timestamp data to the stack.
+ * hardware reset or when a new timestamp value is captured.
+ *
+ * Some PHY types do not provide a "ready" bitmap indicating which timestamp
+ * indexes are valid. In these cases, we use a cached_tstamp to keep track of
+ * the last timestamp we read for a given index. If the current timestamp
+ * value is the same as the cached value, we assume a new timestamp hasn't
+ * been captured. This avoids reporting stale timestamps to the stack. This is
+ * only done if the verify_cached flag is set in ice_ptp_tx structure.
  */
 struct ice_tx_tstamp {
 	struct sk_buff *skb;
@@ -114,6 +119,7 @@ struct ice_tx_tstamp {
  * @init: if true, the tracker is initialized;
  * @calibrating: if true, the PHY is calibrating the Tx offset. During this
  *               window, timestamps are temporarily disabled.
+ * @verify_cached: if true, verify new timestamp differs from last read value
  */
 struct ice_ptp_tx {
 	spinlock_t lock; /* lock protecting in_use bitmap */
@@ -122,8 +128,9 @@ struct ice_ptp_tx {
 	u8 block;
 	u8 offset;
 	u8 len;
-	u8 init;
-	u8 calibrating;
+	u8 init : 1;
+	u8 calibrating : 1;
+	u8 verify_cached : 1;
 };
 
 /* Quad and port information for initializing timestamp blocks */