ice: ensure periodic output start time is in the future

JIRA: https://issues.redhat.com/browse/RHEL-29207

Conflicts:
- adjusted context conflict due to missing 9146394 ("ice: Add
  in/out PTP pin delays")

Upstream commit(s):
commit 53ce716
Author: Karol Kolacinski <[email protected]>
Date:   Wed Feb 19 14:13:27 2025 -0800

    ice: ensure periodic output start time is in the future

    On E800 series hardware, if the start time for a periodic output signal is
    programmed into GLTSYN_TGT_H and GLTSYN_TGT_L registers, the hardware logic
    locks up and the periodic output signal never starts. Any future attempt to
    reprogram the clock function is futile as the hardware will not reset until
    a power on.

    The ice_ptp_cfg_perout function has logic to prevent this, as it checks if
    the requested start time is in the past. If so, a new start time is
    calculated by rounding up.

    Since commit d755a7e ("ice: Cache perout/extts requests and check
    flags"), the rounding is done to the nearest multiple of the clock period,
    rather than to a full second. This is more accurate, since it ensures the
    signal matches the user request precisely.

    Unfortunately, there is a race condition with this rounding logic. If the
    current time is close to the multiple of the period, we could calculate a
    target time that is extremely soon. It takes time for the software to
    program the registers, during which time this requested start time could
    become a start time in the past. If that happens, the periodic output
    signal will lock up.

    For large enough periods, or for the logic prior to the mentioned commit,
    this is unlikely. However, with the new logic rounding to the period and
    with a small enough period, this becomes inevitable.

    For example, attempting to enable a 10MHz signal requires a period of 100
    nanoseconds. This means in the *best* case, we have 99 nanoseconds to
    program the clock output. This is essentially impossible, and thus such a
    small period practically guarantees that the clock output function will
    lock up.

    To fix this, add some slop to the clock time used to check if the start
    time is in the past. Because it is not critical that output signals start
    immediately, but it *is* critical that we do not brick the function, 0.5
    seconds is selected. This does mean that any requested output will be
    delayed by at least 0.5 seconds.

    This slop is applied before rounding, so that we always round up to the
    nearest multiple of the period that is at least 0.5 seconds in the future,
    ensuring a minimum of 0.5 seconds to program the clock output registers.

    Finally, to ensure that the hardware registers programming the clock output
    complete in a timely manner, add a write flush to the end of
    ice_ptp_write_perout. This ensures we don't risk any issue with PCIe
    transaction batching.

    Strictly speaking, this fixes a race condition all the way back at the
    initial implementation of periodic output programming, as it is
    theoretically possible to trigger this bug even on the old logic when
    always rounding to a full second. However, the window is narrow, and the
    code has been refactored heavily since then, making a direct backport not
    apply cleanly.

    Fixes: d755a7e ("ice: Cache perout/extts requests and check flags")
    Signed-off-by: Karol Kolacinski <[email protected]>
    Signed-off-by: Jacob Keller <[email protected]>
    Tested-by: Rinitha S <[email protected]> (A Contingent worker at Intel)
    Signed-off-by: Tony Nguyen <[email protected]>

Signed-off-by: Petr Oros <[email protected]>

Author: orosp

drivers/net/ethernet/intel/ice/ice_ptp.c

@@ -1772,6 +1772,7 @@ static int ice_ptp_write_perout(struct ice_hw *hw, unsigned int chan,
 				  8 + chan + (tmr_idx * 4));
 
 	wr32(hw, GLGEN_GPIO_CTL(gpio_pin), val);
+	ice_flush(hw);
 
 	return 0;
 }
@@ -1831,9 +1832,10 @@ static int ice_ptp_cfg_perout(struct ice_pf *pf, struct ptp_perout_request *rq,
 		div64_u64_rem(start, period, &phase);
 
 	/* If we have only phase or start time is in the past, start the timer
-	 * at the next multiple of period, maintaining phase.
+	 * at the next multiple of period, maintaining phase at least 0.5 second
+	 * from now, so we have time to write it to HW.
 	 */
-	clk = ice_ptp_read_src_clk_reg(pf, NULL);
+	clk = ice_ptp_read_src_clk_reg(pf, NULL) + NSEC_PER_MSEC * 500;
 	if (rq->flags & PTP_PEROUT_PHASE || start <= clk - ice_prop_delay(hw))
 		start = div64_u64(clk + period - 1, period) * period + phase;